May 30, 2024 • 40 mins
How much do you really know about the light that nurtures your plants? In this enlightening episode of Plants, People, Science, hosts Curt Rom and Samson Humphrey take you on a journey through the multifaceted world of light's influence on horticulture. They start with their own personal experiences with sunlight and artificial light, setting the stage for an in-depth discussion with Dr. Erik Runkle from Michigan State University. Dr. Runkle shares his fascinating journey into the study of light and its effects on plant growth, detailing how light intensity, quality, and duration play critical roles in flowering and biomass production. We also tackle the technological advancements that have revolutionized lighting, particularly the shift from traditional bulbs to cutting-edge LED technology.
For more information on the ASHS 2022 Workshop "What Is Far-Red Light's Role in Plant Science?" go to https://ashs.confex.com/ashs/2022/meetingapp.cgi/Session/11349.
Learn more about the American Society for Horticultural Science (ASHS) at https://ashs.org/.
HortTechnology, HortScience and the Journal of the American Society for Horticultural Science are all open-access and peer-reviewed journals, published by the American Society of Horticultural Science (ASHS). Find them at journals.ashs.org.
Consider becoming an ASHS member at https://ashs.org/page/Becomeamember!
You can also find the official webpage for Plants, People, Science at ashs.org/plantspeoplesciencepodcast, and we encourage you to send us feedback or suggestions at https://ashs.org/webinarpodcastsuggestion.
Podcast transcripts are available at https://plantspeoplescience.buzzsprout.com.
On LinkedIn find Sam Humphrey at linkedin.com/in/samson-humphrey. Curt Rom is at https://www.linkedin.com/in/curt-rom-611085134/. Lena Wilson is at https://www.linkedin.com/in/lena-wilson-2531a5141/.
Thank you for listening!
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Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Curt Rom (00:08):
Welcome to Plants, people Science a podcast of the
American Society forHorticulture Science, where we
talk about all thingshorticulture.
I'm Kurt Rohm from theUniversity of Arkansas, your co
-host, along with our co-hostSamson Humphrey from North
Carolina State University.
Sam, how have you been?
Sam Humphrey (00:26):
I've been all right, kurt, but admittedly I
haven't gotten to see muchnatural light recently.
I've been under electricallights writing on my laptop
screen.
I'm finishing up my master'sright now, so, honestly, I've
mostly been inside just doing alot of writing.
How about?
Curt Rom (00:44):
you.
Well, you know I'm a little bitof the opposite.
The semester's ended and I'minto my summer work, so there's
a lot of field work and then mymajor hobby of gardening, so I'm
out under bright sunlight a lotand you know, plants are green,
the flowers are blooming, daysare really long.
(01:05):
That always makes me thinkabout light and you know light
and photosynthesis weresomething that I've spent a lot
of my career studying, so Iguess I enjoy being in the light
.
I don't photosynthesize, but Isure like sunlight.
Sam Humphrey (01:19):
If anyone could photosynthesize, Kurt, I think
it would be you.
Curt Rom (01:22):
Well, I hope that you're prospering under
electrical light.
I know that's the part of yourcareer that you're in and you'll
soon be doing other things aswell and hopefully you get out
into some natural sunlight.
But you know, light is soimportant to plants and so
important to how we grow plants.
Sam Humphrey (01:41):
It is, and the research that I've done and that
many other people do has shownthat if you change the quality,
the color, the intensity oflight in electrical lighting,
you can maybe mimic sunlightbetter or maybe you can cause
plants to respond differently.
So that's a little bit of whatwe'll be talking about today.
Curt Rom (02:03):
Yeah, you know I get really excited about that In my
career.
You know we started withhigh-pressure sodium bulbs and a
lot of conversation about thatmercury vapor bulbs.
But now, with really theintroduction of LED lighting and
although LEDs have been aroundfor quite a long time, the
(02:23):
affordability of it, the abilityto control light, there's a
whole new kind of path andavenue of research and
understanding how we, how plants, respond to light and how we
can control that modified plantgrowth and productivity.
Sam Humphrey (02:40):
Yeah, there's been a real boom in lighting
research and you really see thatat ASHS conferences as well.
Over the past couple decadesthere have been many more
researchers presenting theirlight research at these ASHS
conferences and publishing inthe ASHS journals.
Curt Rom (02:52):
Yeah, I'm excited we had that symposium at the recent
conference on Far Red Light, somaybe we ought to just dig into
this episode and hear what DrRunkle has to say.
Sam Humphrey (03:15):
Dr.
Runkle, welcome to the podcast.
Erik Runkle (03:18):
Thanks, Sam, pleasure to be here.
Sam Humphrey (03:20):
Do you think you could start by briefly
introducing yourself?
Erik Runkle (03:23):
Yeah, my name is Eric Runkle.
I'm a professor and extensionspecialist working in greenhouse
and floriculture crops.
I'm at Michigan StateUniversity and have been in the
department over 20 years now,and I have a research and
extension appointment.
So most of my research isapplied and hopefully serves to
help the industry in some way,shape or form in the short to
(03:45):
medium-term future.
Curt Rom (03:46):
Dr.
Runkle as a colleague I've beenwatching your career, but for
our audience, why don't you tellus a little bit about your area
of study, your discipline, andyou and I share the interest in
light and plant response tolight, so maybe can you tell us
how did you get interested inplants and light?
Erik Runkle (04:04):
Great question, Curt.
It was really my master'sdegree, my master's thesis
research, where I was introducedto light and I studied the
effects of day length onflowering of a wide range of
herbaceous perennials, and so Igained an appreciation for how
light can regulate flowering,the flowering process in a wide
variety of plants, and how itvaries quite a bit from one crop
(04:26):
to another.
And then it was my PhD researchthat continued on the theme of
light, but the focus there waslooking at how different wave
bands or colors of lightinfluence not only growth and
elongation but also floweringresponses.
And so when we studied light,it was back then.
We didn't have LEDs, theyweren't common, they weren't
(04:49):
viable for research, and so welooked at what happens when you
remove certain colors of lightfrom the sun, and that was
pretty informative.
It really sparked my curiosityand interest, not only in terms
of light regulating flowering,but light regulating the growth
of plants.
Curt Rom (05:05):
You know I find that interesting.
I think about my career andprobably yours.
There's been so muchdevelopment of the technology
and the science when I think,when I was a master's student
accrued ways, we used to measurelight and you know the
understanding of wavelengths andwe really didn't have good ways
to control it, and now you havethe breakthroughs of being able
(05:25):
to use and measure PAR.
So it's been kind ofinteresting and I find light to
be just a fascinating thing.
I mean, I know that we use itto create energy, we use it for
solar panels, but it'sinteresting that it also
energizes and cues so many plantresponses.
Tell us a little bit more aboutthis.
(05:46):
You know the short day lengthswe have in the winter and leaves
have fallen off the tree.
As a tree physiologist I findthat phenomena interesting.
Tell us some of the responses,the general responses of plants
to light wavelengths andduration, so that our audience
might understand it better.
Erik Runkle (06:06):
Okay, well, how many hours do you have, Curt?
Curt Rom (06:10):
Well, okay, then Just give us the abstract version.
You can keep it brief or maybefocus on the kind of things that
you like to study.
What about light is reallyexciting to you?
Maybe that's the way to go.
Erik Runkle (06:26):
So when I think of light, I think of light as
having three dimensions.
First is the intensity of thelight, which we can measure on
an instantaneous basis, or moreoften we're interested in the
cumulative amount of light, andthat dimension is what primarily
regulates the biomass or thegrowth aspect of a plant.
So it affects shoot thickness,the number of branches, the
(06:46):
rooting.
It can affect things like fruit, fresh weight, harvestable
index.
We think of that as a primaryfactor that affects just plant
growth, shoot and root growth.
The second dimension we think ofis light quality or the
spectrum of light, and that'sreally been my focus, which has
been to look at how blue light,green light, red light, far red
(07:09):
light, uv light influence plantgrowth and flowering in some
cases, and so it affects notonly flowering but the
architecture of a plant, thingslike leaf size, stem elongation,
the overall plant morphology,and then, of course, the third
dimension is day length or photoperiod and the number of hours
(07:29):
of light and darkness per dayand for a lot of crops, and
especially ornamentals, that canregulate the flowering process.
So we have short day plantsthat flower when the nights are
long and the days are short.
More commonly, with ornamentals, we see they have a long day
response, meaning they flowerwhen the days are short.
More commonly, with ornamentals, we see they have a long day
response, meaning they flowerwhen the days are long and the
nights are short.
Curt Rom (07:49):
But you know, as a human, not as a plant, I always
feel like I'm kind of limitedbecause I can just see visible
light and you know that visiblespectrum is pretty small.
But what you're telling us isthat plants perceive light maybe
more than visible light that wecan see.
And again, in my area I'vealways focused on photosynthetic
(08:10):
light.
So I was looking at, you know,the traditionally and
historically what we've calledphotosynthetic active radiation,
approximately in thewavelengths of 400 to 700
nanometers.
But tell us more about theouter bands, the ultraviolet,
the far red and the infraredwavelengths.
Erik Runkle (08:31):
Sure, yeah.
So it's not surprising thatwe're biased to understanding
light based upon our ownexperiences with it.
And it turns out that the humaneye is very biased towards light
and we see green light verywell.
It appears very bright to us.
We have very good perception ofgreen light, much less so as we
(08:52):
get to shorter or longerwavelengths.
So we do see blue, obviously wesee red light, but if we
consider the number of photonsof blue and red, it appears much
dimmer to us than if we had thesame number of photons of green
.
And then, right when we getinto the UVA region and so that
(09:14):
would be on the shorterwavelength, around 400
nanometers or less we get to apoint where we can't see it
anymore, and so that's on thehigh energy wavelength side of
the spectrum.
On the lower energy but higherwavelength side, we have far red
light, and again, we can'tperceive that by our eye, but
(09:34):
plants are very responsive toboth UV light and far red light,
and so we have to be careful.
And actually, until somewhatrecently, there was a human bias
in recording and measuringlight, because we were basing it
upon the human eye and not onphotons, which is really what
plants respond to in terms ofgrowth and in terms of
(09:57):
morphology.
Sam Humphrey (10:00):
Right.
So today we're talking aboutthe number of photons that are
reaching plants and the colorsof those photons and how they
affect plants differently.
We reached out to you becausewe're really excited to hear
about far red, far red radiation, so could you elaborate a bit
on how far red affects plants?
Erik Runkle (10:23):
Right.
So we can define far red indifferent ways.
Most commonly it's defined asthe wavelength from 700 to 800
nanometers, or I thinkincreasingly some are suggesting
we should shorten that so it's700 to 750 nanometers.
Actually, there's a similaramount of far red coming from
the sun, as there is with redlight as well as green and blue
(10:46):
light, and so it has apronounced effect on the shape
of the plant, and some of theearliest work we did with LEDs
actually was looking at far redlight and how it and other
colors of light control theflowering process of plants that
are responsive to day lengthfor flowering.
So far red is known to elicitwhat we call shade avoidance
(11:09):
responses.
So these are responses that whena plant perceives shade and
usually that's what can be fromdifferent ways, but one of the
most common ones is when there'sa relative abundance of far red
light relative to other colorsof light and especially relative
to the amount of red light.
So when we have a relativeabundance of far red light
relative to other colors oflight and especially relative to
the amount of red light, sowhen we have a relative
abundance of far red light, thegrowth response of the plant is
(11:32):
well, it's a signal that theplant now needs to respond to
capture sunlight that'savailable or whatever light is
available, and so it's aresponse, kind of a flight or
fight response.
And so it can't fly, so it'sgot to fight, and so what the
plants will typically do is theleaves become larger, the
(11:52):
petioles elongate, the leaf areaincreases and if it has a stem,
the stems elongate as well, andso it's really trying to expand
itself to try to capture thephotosynthetic light that is
available.
Expand itself to try to capturethe photosynthetic light that
is available.
Sam Humphrey (12:06):
So maybe a plant at the bottom of the canopy
might be getting less of thatred light, less of those other
colors and maybe a greaterproportion of far red.
And so it does this stretchingeffect to reach and get more
light.
Erik Runkle (12:21):
You said it just right, Sam.
So leaves absorb most of thegreen, blue and red light, but
they transmit or reflect most ofthe far red light, and so
that's why the ratio of far redto the other colors changes as
it penetrates through a canopy.
Curt Rom (12:37):
Erik, you know, and as I said previously, technology
has really changed, both in ourability to measure light and
light intensity, as well as thewavelengths of light, and now we
actually, with LEDs, havebetter ability to control light
for plants.
I mean, we've gone from using asledgehammer to tweezers on
this.
(12:57):
How is this technology, both inthe ability to measure light
and the ability to control light, opening up new areas of
science, new aspects ofhorticulture for us?
Are we becoming illuminated?
Erik Runkle (13:14):
That we are, Curt.
Yeah, so really, theadvancements of LEDs in terms of
their output that has beenincreasing and their cost that
has been decreasing, has reallyenabled a new frontier of
research with lighting 1980swith LEDs.
(13:38):
But that was by a select few,specifically those involved with
NASA, where they had a, let'ssay just say, a healthy budget
to work with LEDs, and so thatprovided some very important
foundational research wherepeople were able to deliver very
specific wavelengths andspecific intensities to really
(14:00):
understand the fundamentals ofplant growth and how different
colors of light influence plantgrowth.
And then, as the technology ofLEDs has advanced and it really
picked up around 2010, we'veseen the number of researchers
getting into lighting hasdramatically increased and with
(14:21):
that, our understanding of howthe different colors of light,
the intensity of light and howthose interact with each other
to regulate different growth anddevelopment processes of plants
.
So it's given us a reallypowerful way to manipulate the
light spectrum and intensity atthe same time.
And it's one of those thingsthat the more you learn about
(14:44):
light, the more questions youhave.
And so, while there are a lotof people who are looking at
lighting, looking atunderstanding light and effects
on plants, there's still not ashortage of research areas to
pursue.
Sam Humphrey (15:00):
And it's exciting too, because so many of those
research areas are so close tophysics.
I had my first introduction tohorticulture through agronomy
and it's always been very plantfocused, but then, when I first
started learning about lighting,it was so much more physics
than I ever expected.
So it's really wonderful to seethese two fields very closely
(15:26):
related through light.
But it also brings up somereally interesting questions of
how physicians, how physicsprofessors understand light and
how horticulturalists and plantsunderstand light, and has
brought questions about, forexample, par and if we should
(15:49):
extend PAR.
Could you elaborate a littlebit about that?
Erik Runkle (15:54):
Yeah, so PAR is an acronym for photosynthetically
active radiation, forphotosynthetically active
radiation, and it was so.
The foundation of it was basedon some pioneering research
performed by Keith McCree wherehe looked at the effects of
different colors of light onrelative photosynthesis, and it
(16:23):
was very important research.
It had its limitations, but ofcourse this was done before LEDs
were available.
And so, looking at the growthresponse on an instantaneous
basis, looking at all the wayfrom the UV range up to the
far-red range, we could see thatarbitrarily you could select
the wave band from 400 to 700nanometers as the region that is
(16:47):
what's most effective atincreasing plant growth Now.
So because of that, thedefinition for PAR considers
that all photons in that waveband from 400 to 700 nanometers
are equally effective atincreasing photosynthesis and
thus plant growth.
(17:10):
Now there has been more researchwith far-red, especially in the
last 10 years, as far-red LEDshave become more common, and it
has enhanced our understandingof how far-red light not only
affects morphological responsessuch as plant acclimation, but
also how it affectsphotosynthesis, and there's a
(17:33):
well-known response called theEmerson Enhancement Effect that
has shown that the simultaneousdelivery of far-red and red
light is better than one or theother, and so we've known that
far-red is important forphotosynthesis.
But I think, with thisadditional research with far-red
, there are some studies thatshow that far-red photons in
(17:56):
some cases are equally effectiveat stimulating photosynthesis
as red photons or green or bluephotons, and so there's some
effort that we need to extendthe definition of PAR to 750
nanometers.
Some might even suggest 800nanometers, but hence the term
(18:18):
extended PAR or e EPAR, where inthat case the far-red photons
would be considered equal to red, green and far-red photons.
Curt Rom (18:28):
As you've seen, sometimes science moves at a
glacial pace because we have tohave scientific fact and then
prove a theory and we have tohave a preponderance of evidence
.
So it's really difficult tochange paradigms like the
paradigm of PAR being just 400to 700 plus or minus nanometers,
(18:51):
I guess.
Now has this new evidence?
How are the scholars reviewingthis?
Is there skepticism about thenew discoveries?
Is it stimulating more work?
Are people in general agreement?
Tell us what kind of state ofthe science is?
We don't have relatively newfindings.
(19:13):
Is there a preponderance ofevidence starting to build?
Does my question?
Do you understand what I'masking?
Erik Runkle (19:20):
And does my question?
Do you understand what I'masking?
Yeah, yeah, I do, andfortunately those of us working
in this area, it's a relativelysmall community and it's a great
community.
There's a lot of mutual respect, and actually that was one of
the topics that we discussed atthe last ASHS meeting, where we
(19:41):
had a workshop focused onFAR-RED and one of the main
focal points was to discuss PARand ePAR and what people's
thoughts were between the twoand advantages and disadvantages
of each, and so the concept ofePAR really has been pioneered
by Bruce Bugbee at Utah StateUniversity and Mark Van Ersel at
(20:04):
University of Georgia, wherethey performed some pretty
compelling research along withtheir graduate students and
postdocs.
That showed very well thatthere was a promotion of
photosynthesis with the additionof FAR-RED and, of course, that
supplements some of the earlierwork.
(20:24):
So, as more people have studiedthis, I think there has been a
growing consensus that we needto, at a minimum, report
extended PAR or ePAR.
I don't know if we necessarilyneed to not report PAR by itself
, and I think in the best worldpeople are reporting PAR and
(20:46):
ePAR, and for that you might aswell report specific percentages
of other colors of light likeblue, green and red.
So there's a movement towardsPAR.
There is also some caution,including by me, because let's
take an extreme case where, okay, we know we can grow plants
(21:06):
under only blue or only green oronly red light.
Their morphology may be prettyfunky.
But can we grow a plant underonly high intensity, far red
light?
And okay, maybe you could, butit's not going to be Anyway.
So it becomes a little bitsubjective.
(21:28):
So I think there may be someconstraints with EPAR, but I
think including it as a metricis very compelling in scientific
research.
Sam Humphrey (21:39):
So in this workshop, I love thinking about
this because I have been taughtthat, as Curt said, science
moves at a glacial pace and wepublish papers and build upon
each other's work and showevidence and it's sort of a slow
(21:59):
process all things considered.
But then at ASHS Conference2022, you held a workshop where
all these scientists who havebeen doing this work and have
spent their whole careerslooking at and trying to
understand plants and light andthe interactions they all got
(22:19):
together in a room to discuss.
So I find that so valuable.
Thank you for running thatworkshop.
I'm wondering if you could justdescribe simply the outcome of
that workshop discussion.
Erik Runkle (22:36):
Yeah.
So we had speakers where theygave basic overviews of the
different effects of far-redlight in the growth and
flowering process.
So the focus was very clearlyon far-red light.
And then we had a lot of timefor, I would say, debate and
discussion, although therewasn't a whole lot of debate,
(23:03):
wasn't a whole lot of debate,but people sharing their
thoughts and experiences andresearch with Far Red and the
merits of including Far Red inthe spectrum, in the spectrum
that we should be reporting inplant science.
And there were people it was avery well attended workshop a
lot of academics, a lot ofgraduate students and I was glad
to see also quite a few fromindustry.
(23:24):
And if you think about industry, you know they're creating
these LED fixtures and whetherwe consider far red in industry
being light that is useful forplants can really drive the
design of these differentfixtures for various reasons,
and so I was pleased to see thatthere were lighting companies
(23:46):
in particular that were at thisworkshop, and so I think we
walked away with a generalconsensus and agreement that far
red light, as we know, has abig role in the growth cycle of
plants and that we should bereporting it.
And there's still somequestions about whether, when
(24:10):
you design treatments, youshould have treatments that have
equal number of photons in thePAR region, or do you include
also far-red light?
So there's still different waysto do research.
One is not necessarily right orwrong.
It's more important that youclearly define your wave bands
in your treatments and the basisfor those treatments.
Curt Rom (24:33):
Again.
I find that very interesting,Dr.
Runkle.
One of the things abouthorticulture that our sciences
are both fundamental andtranslational.
They're applicable.
What do you see?
I've got two questions and youcan answer them in any order you
want.
What is the frontier of thisnew light science and what are
(24:55):
the new questions that areemerging from our discoveries?
That's one kind of thing I'dlike to address.
The other is so what you know,so what we now know this, but
how do we apply this and wheredoes this information fit?
Is it useful or is it just somesort of arcane knowledge?
Erik Runkle (25:17):
Well, I certainly hope it's not arcane knowledge.
So let me get to your firstquestion the frontiers of this
research.
And I don't have a real clearcrystal ball on that.
I think there are a lot ofquestions that we still have,
and some of those questions arelimited by LEDs and what peak
(25:38):
wavelengths are available forfar-right LEDs.
And so there's really one majortype of far-right LED.
It has an emission peak that isaround 730 nanometers.
I think there's a need for moreresearch where the peak
wavelengths are beyond that,both lower or higher.
I think we generally understandthat once you get beyond 750 or
(26:02):
760 nanometers, that there'sless or perhaps no utility of
those photons with respect togrowth or development of a plant
.
But I think we need tounderstand much better than just
subjectively choosing 750,because it's a round number, to
have a little more sciencebehind where that cutoff is for
(26:23):
the higher wavelength.
So I think that's one thingthat again is going to be
limited by technology.
However, I do think there aresome other approaches that we
can tackle that problem.
Also, I think questions aboutfar red and interactions with
other colors of light.
So far, red and blueinteractions are something that
(26:44):
I'm studying and very interestedin Blue and far red light in
some ways act antagonistically.
So blue light typicallysuppresses growth and elongation
.
Far red light typicallypromotes elongation.
And so then you have thisinteraction between the two, and
which one wins right, which onecan offset the other, and so
(27:08):
complexities that exist withother colors, as well as far-red
interaction, just with absolutenumber of photons, so light
quantity, and whether or not thefar-red light effects diminish
as light intensity increases ornot.
So those are, just off the topof my head, some of the areas
I'm personally interested in andI think there's still questions
(27:30):
about In terms of what doesthis all mean?
Of course, it means more for uswho are in plant science and
lighting research than manyothers, but I think, ultimately,
what we want is to createenvironments to grow plants
where we are maximizing growthwhile considering inputs.
(27:51):
And so if we're growing plantsin a greenhouse or indoors, in
cases where we are enriching thespectrum, for example, with
supplemental lighting, in caseswhere we are enriching the
spectrum, for example, withsupplemental lighting, the
question of delivering far-redlight or not can have an
economic impact on the crop.
(28:16):
It can affect the qualityattributes, potentially the
harvestable yield, things thatwill matter to the people who
are growing the plants andultimately to the consumer.
So we are understanding far-redand the effects and, of course,
not everything is good.
I mean there are sometrade-offs that exist with far
red is that you may get biggerleaves, for example, but it
could come at the consequence ofchanging the texture of a leaf.
If it's something you might eat, like a lettuce, it can
decrease the coloration of aleaf, so a leaf may not be as
(28:38):
dark green or as purple.
Decrease the coloration of aleaf, so a leaf may not be as
dark green or as purple with farred.
And so, understanding all ofthese effects of far red light,
knowing that there will be sometrade-offs, and keeping in mind
when we're growing horticulturalcrops, we want to make sure
that we're not resulting in aninferior product when it's sold
to consumers.
Curt Rom (28:57):
It makes sense why it started with NASA and their
technology.
Of course we want to feedpeople in space stations.
We want to go to Mars.
You have a very compellingargument that this will have an
impact on feeding 8 to 10billion people in the next 30
years if we do more protectedagriculture.
So it is very fundamental, butalso very applied.
(29:20):
It really has significantimpact because I do pay
attention to what my lettuce islike.
I have one more question.
It's not necessarily in yourarea, but just was curious.
You know when we think aboutplants absorbing light.
The primary antenna for lightabsorption has been a specific
(29:41):
kind of pigment.
In the case of photosynthesisit's chlorophyll for absorbing
PAR.
Have phytochemists identifiedpigment systems or other
chemical systems that areperceiving or absorbing these
other wavelengths of light?
I just don't understand.
Where is it chlorophyll?
Erik Runkle (30:01):
other wavelengths of ligh
Chlorophyll, yeah, so far-red,of course, can be useful in
photosynthetic reactions,especially lower-energy far-red,
so 700, 710 region.
But then there's phytochrome,which are the pigments in all
(30:23):
plants, at least light-grownplants, that perceive the ratio
of red and far-red light, andthere are several types of
phytochromes, and it's been veryextensively studied in
Arabidopsis, looking at mutantsof individual phytochromes and
understanding what happens whenthese plants lack one or more of
(30:44):
these phytochromes and howgrowth is different from a plant
that has the full phytochromecomponents.
One of the challenges thatexists, though, is that a lot of
this research is based onArabidopsis, which is a weed,
which is a plant with a veryshort crop cycle Seed to flower
(31:08):
is four weeks, for example.
So, knowing phytochromeresponses in Arabidopsis and, of
course, other plants too, thereare certainly some similarity,
but there are also somedifferences that can exist from
one crop to another phytochrome.
(31:28):
We will continue to improve ourunderstanding of the role of
phytochrome in mediating theseresponses to far red as well as
other colors of light, such asred light.
Sam Humphrey (31:48):
That's wonderful.
Thank you, Erik.
It's also interesting too,because phytochrome also absorbs
within blue wavelengths, right,and so there's so much research
.
Again, I was excited to hearthat you're interested in blue
and far red in combination inyour research.
So there's so many thingspeople could study, so many
(32:12):
different crops, so manydifferent wavelengths of light
and combinations like you weretalking about.
It's really exciting to seethis work evolve, combinations
like you were talking about.
It's really exciting to seethis work evolve If you were a
student and you listened to thispodcast and learned about how
the colors of light affectplants and if you wanted, to
(32:32):
learn more.
Curt Rom (32:32):
Where would you go?
Erik Runkle (32:35):
I mean the first impulse is to go to the internet
right and start typing inkeywords that are of most
interest to you.
So that could include far red,if that's what's exciting, or
blue colors or light qualityType in crops that might be of
particular interest to you, tosee if maybe there's a
combination of keywords, when astudy has been performed on that
(32:56):
, especially for horticulturalcrops, been performed on that,
especially for horticulturalcrops.
So that would be probably morefor the plant science side.
Go into Google Scholar andstart typing in keywords and
seeing what's the most, what arethe most recent papers that
have been published the lastfive years, for example.
So that's at least my go-to ofhow to find information is just
(33:17):
going to the internet and doinga search.
There are also ways you couldlearn about the people who are
doing this research and thereare quite a few in the United
States as well as several other,many other countries to learn
what their active researchprograms are studying.
So that's the scientific side.
(33:40):
If people are more interestedon the application side, there
are a lot of grower articles outthere that I and many of my
colleagues have written aboutlight and plants and
specifically about far red, forthose who might be interested,
or other colors of light, and sothat can be information that's
a little more digestible, rightPapers or articles that have
(34:08):
been written for not ascientific audience but maybe a
more professional audience or anindustry audience.
So I guess that would be myapproach.
I actually, sam, I'd beinterested to see I mean, you're
, you're interested in this areawhat?
What are ways that you try tofind information and seek more
information about like quality?
Sam Humphrey (34:27):
I'm a little bit biased, Dr.
Runkle.
Um, I would go to ashsorg andfind the journals tab where ASHS
has three journals where theypublish publications relevant to
this, and I would search thatspecifically because I know
those papers are of high qualityand I know you've published in
those journals as well.
(34:47):
I would say sometimes you canfind scientists who make amazing
extension materials, like Dr.
Bugbee, as you mentionedearlier in this interview.
He hasa website where hepublishes some of his lectures
that he's given to classes, andyou can watch some of those
online lectures and abstractsand things from previous ASHS
(35:12):
conferences.
So that's where I would go, inaddition to what you described.
Curt Rom (35:19):
That's where I would go in addition to what you
described, speaking about ourjournals with this kind of new
information and newconsiderations?
Are you visiting with editorsand reviewers that, instead of
just saying I measured PAR, theyshould start reporting the
wavelengths that they measure,the technology that was used to
(35:39):
measure that?
Erik Runkle (35:39):
I mean, I've got a bunch of PAR sensors that aren't
going to measure what I mightneed to measure now you know
that that comes up when I'mreviewing papers that are
focused on light quality, and soif they're studying that, then
I think it's an you know, it'san absolute expectation that
(36:00):
they have measured the lightspectrum and are reporting it,
and so they would include blue,green, red and far red light,
and even if they're not studyingfar red, it would be important
to know the lamp type or some ofthe characteristics so that if
we wanted to find thatinformation ourselves, the
information was available.
So if we were to review a paper,whether it's for an ASHS
(36:22):
journal or another, that's theopportunity we have to provide
feedback, and if we feel verystrongly about something, we can
write a short justification formaybe a fundamental flaw,
that's sent to the editor sothat they know that this is a
pretty important aspect that haseither not been reported or
perhaps even overlooked In termsof you know how we try to move
(36:48):
this forward with ePAR.
I think you know we go to a lotof the same meetings, ASHS
meetings.
We see a lot of our colleaguesand talk about these things in
their papers and presentationsfocused on PAR, and there we can
emphasize the importance ofreporting PAR and ePAR when it's
relevant, as well as in papers.
(37:10):
You know we can talk about PARand ePAR in the same breath, and
when we have opportunities totalk about PAR, whether it's
with colleagues in academia,graduate students or industry,
we can talk about FAR-RED, Someof the advantages and
disadvantages, and, when itcomes to reporting, when and
(37:30):
when it may not matter- Well,this has been very enlightening
if I can say that with astraight face.
Curt Rom (37:37):
You know it's been informative and fun.
If I can say that with astraight face, you know it's
been informative and fun.
Like I've said, I became ahorticulture physiologist
because I heard an interestinglecture on light in an
undergraduate physiology class,and so is this, you know, the
kind of additional step for meunderstanding and learning about
the impact of light, and I cansee it.
(37:59):
It's opened my eyes for real.
I understand light a little bitbetter.
Sam, what do you think?
Sam Humphrey (38:09):
I really love this conversation.
I love talking about light ingeneral, so it's not a surprise,
but hearing from one of thescientists that's at the
forefront and who is helpingdrive this conversation,
promoting good science andtrying to move the needle
(38:29):
forward with our understandingof how plants respond to light.
It's just wonderful to talkwith you, Dr.
Runkle.
Curt Rom (38:47):
The ASHS podcast Plants, People, Science is made
possible by member dues andvolunteerism.
Please go to ashs.
org to learn more.
If you're not already a memberof the ASHS, we invite you to
join.
ASHS is a not-for-profit andyour donations are tax
deductible.
Sam Humphrey (39:05):
This episode was hosted by Samson Humphrey and
Curt Rom.
Special thanks to our audioengineer, Andrew Sheldorf, our
research specialists Lena Wilsonand Andrew Sheldorf, our ASHS
support team, Sara Powell andSally Murphy, and our musician
John Clark.
Thanks for listening.
Thank you.
Welcome to Plants, people Science a podcast of the
American Society forHorticulture Science, where we
talk about all thingshorticulture.
I'm Kurt Rohm from theUniversity of Arkansas, your co
-host, along with our co-hostSamson Humphrey from North
Carolina State University.
Sam, how have you been?
Sam Humphrey (00:26):
I've been all right, kurt, but admittedly I
haven't gotten to see muchnatural light recently.
I've been under electricallights writing on my laptop
screen.
I'm finishing up my master'sright now, so, honestly, I've
mostly been inside just doing alot of writing.
How about?
Curt Rom (00:44):
you.
Well, you know I'm a little bitof the opposite.
The semester's ended and I'minto my summer work, so there's
a lot of field work and then mymajor hobby of gardening, so I'm
out under bright sunlight a lotand you know, plants are green,
the flowers are blooming, daysare really long.
(01:05):
That always makes me thinkabout light and you know light
and photosynthesis weresomething that I've spent a lot
of my career studying, so Iguess I enjoy being in the light
.
I don't photosynthesize, but Isure like sunlight.
Sam Humphrey (01:19):
If anyone could photosynthesize, Kurt, I think
it would be you.
Curt Rom (01:22):
Well, I hope that you're prospering under
electrical light.
I know that's the part of yourcareer that you're in and you'll
soon be doing other things aswell and hopefully you get out
into some natural sunlight.
But you know, light is soimportant to plants and so
important to how we grow plants.
Sam Humphrey (01:41):
It is, and the research that I've done and that
many other people do has shownthat if you change the quality,
the color, the intensity oflight in electrical lighting,
you can maybe mimic sunlightbetter or maybe you can cause
plants to respond differently.
So that's a little bit of whatwe'll be talking about today.
Curt Rom (02:03):
Yeah, you know I get really excited about that In my
career.
You know we started withhigh-pressure sodium bulbs and a
lot of conversation about thatmercury vapor bulbs.
But now, with really theintroduction of LED lighting and
although LEDs have been aroundfor quite a long time, the
(02:23):
affordability of it, the abilityto control light, there's a
whole new kind of path andavenue of research and
understanding how we, how plants, respond to light and how we
can control that modified plantgrowth and productivity.
Sam Humphrey (02:40):
Yeah, there's been a real boom in lighting
research and you really see thatat ASHS conferences as well.
Over the past couple decadesthere have been many more
researchers presenting theirlight research at these ASHS
conferences and publishing inthe ASHS journals.
Curt Rom (02:52):
Yeah, I'm excited we had that symposium at the recent
conference on Far Red Light, somaybe we ought to just dig into
this episode and hear what DrRunkle has to say.
Sam Humphrey (03:15):
Dr.
Runkle, welcome to the podcast.
Erik Runkle (03:18):
Thanks, Sam, pleasure to be here.
Sam Humphrey (03:20):
Do you think you could start by briefly
introducing yourself?
Erik Runkle (03:23):
Yeah, my name is Eric Runkle.
I'm a professor and extensionspecialist working in greenhouse
and floriculture crops.
I'm at Michigan StateUniversity and have been in the
department over 20 years now,and I have a research and
extension appointment.
So most of my research isapplied and hopefully serves to
help the industry in some way,shape or form in the short to
(03:45):
medium-term future.
Curt Rom (03:46):
Dr.
Runkle as a colleague I've beenwatching your career, but for
our audience, why don't you tellus a little bit about your area
of study, your discipline, andyou and I share the interest in
light and plant response tolight, so maybe can you tell us
how did you get interested inplants and light?
Erik Runkle (04:04):
Great question, Curt.
It was really my master'sdegree, my master's thesis
research, where I was introducedto light and I studied the
effects of day length onflowering of a wide range of
herbaceous perennials, and so Igained an appreciation for how
light can regulate flowering,the flowering process in a wide
variety of plants, and how itvaries quite a bit from one crop
(04:26):
to another.
And then it was my PhD researchthat continued on the theme of
light, but the focus there waslooking at how different wave
bands or colors of lightinfluence not only growth and
elongation but also floweringresponses.
And so when we studied light,it was back then.
We didn't have LEDs, theyweren't common, they weren't
(04:49):
viable for research, and so welooked at what happens when you
remove certain colors of lightfrom the sun, and that was
pretty informative.
It really sparked my curiosityand interest, not only in terms
of light regulating flowering,but light regulating the growth
of plants.
Curt Rom (05:05):
You know I find that interesting.
I think about my career andprobably yours.
There's been so muchdevelopment of the technology
and the science when I think,when I was a master's student
accrued ways, we used to measurelight and you know the
understanding of wavelengths andwe really didn't have good ways
to control it, and now you havethe breakthroughs of being able
(05:25):
to use and measure PAR.
So it's been kind ofinteresting and I find light to
be just a fascinating thing.
I mean, I know that we use itto create energy, we use it for
solar panels, but it'sinteresting that it also
energizes and cues so many plantresponses.
Tell us a little bit more aboutthis.
(05:46):
You know the short day lengthswe have in the winter and leaves
have fallen off the tree.
As a tree physiologist I findthat phenomena interesting.
Tell us some of the responses,the general responses of plants
to light wavelengths andduration, so that our audience
might understand it better.
Erik Runkle (06:06):
Okay, well, how many hours do you have, Curt?
Curt Rom (06:10):
Well, okay, then Just give us the abstract version.
You can keep it brief or maybefocus on the kind of things that
you like to study.
What about light is reallyexciting to you?
Maybe that's the way to go.
Erik Runkle (06:26):
So when I think of light, I think of light as
having three dimensions.
First is the intensity of thelight, which we can measure on
an instantaneous basis, or moreoften we're interested in the
cumulative amount of light, andthat dimension is what primarily
regulates the biomass or thegrowth aspect of a plant.
So it affects shoot thickness,the number of branches, the
(06:46):
rooting.
It can affect things like fruit, fresh weight, harvestable
index.
We think of that as a primaryfactor that affects just plant
growth, shoot and root growth.
The second dimension we think ofis light quality or the
spectrum of light, and that'sreally been my focus, which has
been to look at how blue light,green light, red light, far red
(07:09):
light, uv light influence plantgrowth and flowering in some
cases, and so it affects notonly flowering but the
architecture of a plant, thingslike leaf size, stem elongation,
the overall plant morphology,and then, of course, the third
dimension is day length or photoperiod and the number of hours
(07:29):
of light and darkness per dayand for a lot of crops, and
especially ornamentals, that canregulate the flowering process.
So we have short day plantsthat flower when the nights are
long and the days are short.
More commonly, with ornamentals, we see they have a long day
response, meaning they flowerwhen the days are short.
More commonly, with ornamentals, we see they have a long day
response, meaning they flowerwhen the days are long and the
nights are short.
Curt Rom (07:49):
But you know, as a human, not as a plant, I always
feel like I'm kind of limitedbecause I can just see visible
light and you know that visiblespectrum is pretty small.
But what you're telling us isthat plants perceive light maybe
more than visible light that wecan see.
And again, in my area I'vealways focused on photosynthetic
(08:10):
light.
So I was looking at, you know,the traditionally and
historically what we've calledphotosynthetic active radiation,
approximately in thewavelengths of 400 to 700
nanometers.
But tell us more about theouter bands, the ultraviolet,
the far red and the infraredwavelengths.
Erik Runkle (08:31):
Sure, yeah.
So it's not surprising thatwe're biased to understanding
light based upon our ownexperiences with it.
And it turns out that the humaneye is very biased towards light
and we see green light verywell.
It appears very bright to us.
We have very good perception ofgreen light, much less so as we
(08:52):
get to shorter or longerwavelengths.
So we do see blue, obviously wesee red light, but if we
consider the number of photonsof blue and red, it appears much
dimmer to us than if we had thesame number of photons of green
.
And then, right when we getinto the UVA region and so that
(09:14):
would be on the shorterwavelength, around 400
nanometers or less we get to apoint where we can't see it
anymore, and so that's on thehigh energy wavelength side of
the spectrum.
On the lower energy but higherwavelength side, we have far red
light, and again, we can'tperceive that by our eye, but
(09:34):
plants are very responsive toboth UV light and far red light,
and so we have to be careful.
And actually, until somewhatrecently, there was a human bias
in recording and measuringlight, because we were basing it
upon the human eye and not onphotons, which is really what
plants respond to in terms ofgrowth and in terms of
(09:57):
morphology.
Sam Humphrey (10:00):
Right.
So today we're talking aboutthe number of photons that are
reaching plants and the colorsof those photons and how they
affect plants differently.
We reached out to you becausewe're really excited to hear
about far red, far red radiation, so could you elaborate a bit
on how far red affects plants?
Erik Runkle (10:23):
Right.
So we can define far red indifferent ways.
Most commonly it's defined asthe wavelength from 700 to 800
nanometers, or I thinkincreasingly some are suggesting
we should shorten that so it's700 to 750 nanometers.
Actually, there's a similaramount of far red coming from
the sun, as there is with redlight as well as green and blue
(10:46):
light, and so it has apronounced effect on the shape
of the plant, and some of theearliest work we did with LEDs
actually was looking at far redlight and how it and other
colors of light control theflowering process of plants that
are responsive to day lengthfor flowering.
So far red is known to elicitwhat we call shade avoidance
(11:09):
responses.
So these are responses that whena plant perceives shade and
usually that's what can be fromdifferent ways, but one of the
most common ones is when there'sa relative abundance of far red
light relative to other colorsof light and especially relative
to the amount of red light.
So when we have a relativeabundance of far red light
relative to other colors oflight and especially relative to
the amount of red light, sowhen we have a relative
abundance of far red light, thegrowth response of the plant is
(11:32):
well, it's a signal that theplant now needs to respond to
capture sunlight that'savailable or whatever light is
available, and so it's aresponse, kind of a flight or
fight response.
And so it can't fly, so it'sgot to fight, and so what the
plants will typically do is theleaves become larger, the
(11:52):
petioles elongate, the leaf areaincreases and if it has a stem,
the stems elongate as well, andso it's really trying to expand
itself to try to capture thephotosynthetic light that is
available.
Expand itself to try to capturethe photosynthetic light that
is available.
Sam Humphrey (12:06):
So maybe a plant at the bottom of the canopy
might be getting less of thatred light, less of those other
colors and maybe a greaterproportion of far red.
And so it does this stretchingeffect to reach and get more
light.
Erik Runkle (12:21):
You said it just right, Sam.
So leaves absorb most of thegreen, blue and red light, but
they transmit or reflect most ofthe far red light, and so
that's why the ratio of far redto the other colors changes as
it penetrates through a canopy.
Curt Rom (12:37):
Erik, you know, and as I said previously, technology
has really changed, both in ourability to measure light and
light intensity, as well as thewavelengths of light, and now we
actually, with LEDs, havebetter ability to control light
for plants.
I mean, we've gone from using asledgehammer to tweezers on
this.
(12:57):
How is this technology, both inthe ability to measure light
and the ability to control light, opening up new areas of
science, new aspects ofhorticulture for us?
Are we becoming illuminated?
Erik Runkle (13:14):
That we are, Curt.
Yeah, so really, theadvancements of LEDs in terms of
their output that has beenincreasing and their cost that
has been decreasing, has reallyenabled a new frontier of
research with lighting 1980swith LEDs.
(13:38):
But that was by a select few,specifically those involved with
NASA, where they had a, let'ssay just say, a healthy budget
to work with LEDs, and so thatprovided some very important
foundational research wherepeople were able to deliver very
specific wavelengths andspecific intensities to really
(14:00):
understand the fundamentals ofplant growth and how different
colors of light influence plantgrowth.
And then, as the technology ofLEDs has advanced and it really
picked up around 2010, we'veseen the number of researchers
getting into lighting hasdramatically increased and with
(14:21):
that, our understanding of howthe different colors of light,
the intensity of light and howthose interact with each other
to regulate different growth anddevelopment processes of plants
.
So it's given us a reallypowerful way to manipulate the
light spectrum and intensity atthe same time.
And it's one of those thingsthat the more you learn about
(14:44):
light, the more questions youhave.
And so, while there are a lotof people who are looking at
lighting, looking atunderstanding light and effects
on plants, there's still not ashortage of research areas to
pursue.
Sam Humphrey (15:00):
And it's exciting too, because so many of those
research areas are so close tophysics.
I had my first introduction tohorticulture through agronomy
and it's always been very plantfocused, but then, when I first
started learning about lighting,it was so much more physics
than I ever expected.
So it's really wonderful to seethese two fields very closely
(15:26):
related through light.
But it also brings up somereally interesting questions of
how physicians, how physicsprofessors understand light and
how horticulturalists and plantsunderstand light, and has
brought questions about, forexample, par and if we should
(15:49):
extend PAR.
Could you elaborate a littlebit about that?
Erik Runkle (15:54):
Yeah, so PAR is an acronym for photosynthetically
active radiation, forphotosynthetically active
radiation, and it was so.
The foundation of it was basedon some pioneering research
performed by Keith McCree wherehe looked at the effects of
different colors of light onrelative photosynthesis, and it
(16:23):
was very important research.
It had its limitations, but ofcourse this was done before LEDs
were available.
And so, looking at the growthresponse on an instantaneous
basis, looking at all the wayfrom the UV range up to the
far-red range, we could see thatarbitrarily you could select
the wave band from 400 to 700nanometers as the region that is
(16:47):
what's most effective atincreasing plant growth Now.
So because of that, thedefinition for PAR considers
that all photons in that waveband from 400 to 700 nanometers
are equally effective atincreasing photosynthesis and
thus plant growth.
(17:10):
Now there has been more researchwith far-red, especially in the
last 10 years, as far-red LEDshave become more common, and it
has enhanced our understandingof how far-red light not only
affects morphological responsessuch as plant acclimation, but
also how it affectsphotosynthesis, and there's a
(17:33):
well-known response called theEmerson Enhancement Effect that
has shown that the simultaneousdelivery of far-red and red
light is better than one or theother, and so we've known that
far-red is important forphotosynthesis.
But I think, with thisadditional research with far-red
, there are some studies thatshow that far-red photons in
(17:56):
some cases are equally effectiveat stimulating photosynthesis
as red photons or green or bluephotons, and so there's some
effort that we need to extendthe definition of PAR to 750
nanometers.
Some might even suggest 800nanometers, but hence the term
(18:18):
extended PAR or e EPAR, where inthat case the far-red photons
would be considered equal to red, green and far-red photons.
Curt Rom (18:28):
As you've seen, sometimes science moves at a
glacial pace because we have tohave scientific fact and then
prove a theory and we have tohave a preponderance of evidence
.
So it's really difficult tochange paradigms like the
paradigm of PAR being just 400to 700 plus or minus nanometers,
(18:51):
I guess.
Now has this new evidence?
How are the scholars reviewingthis?
Is there skepticism about thenew discoveries?
Is it stimulating more work?
Are people in general agreement?
Tell us what kind of state ofthe science is?
We don't have relatively newfindings.
(19:13):
Is there a preponderance ofevidence starting to build?
Does my question?
Do you understand what I'masking?
Erik Runkle (19:20):
And does my question?
Do you understand what I'masking?
Yeah, yeah, I do, andfortunately those of us working
in this area, it's a relativelysmall community and it's a great
community.
There's a lot of mutual respect, and actually that was one of
the topics that we discussed atthe last ASHS meeting, where we
(19:41):
had a workshop focused onFAR-RED and one of the main
focal points was to discuss PARand ePAR and what people's
thoughts were between the twoand advantages and disadvantages
of each, and so the concept ofePAR really has been pioneered
by Bruce Bugbee at Utah StateUniversity and Mark Van Ersel at
(20:04):
University of Georgia, wherethey performed some pretty
compelling research along withtheir graduate students and
postdocs.
That showed very well thatthere was a promotion of
photosynthesis with the additionof FAR-RED and, of course, that
supplements some of the earlierwork.
(20:24):
So, as more people have studiedthis, I think there has been a
growing consensus that we needto, at a minimum, report
extended PAR or ePAR.
I don't know if we necessarilyneed to not report PAR by itself
, and I think in the best worldpeople are reporting PAR and
(20:46):
ePAR, and for that you might aswell report specific percentages
of other colors of light likeblue, green and red.
So there's a movement towardsPAR.
There is also some caution,including by me, because let's
take an extreme case where, okay, we know we can grow plants
(21:06):
under only blue or only green oronly red light.
Their morphology may be prettyfunky.
But can we grow a plant underonly high intensity, far red
light?
And okay, maybe you could, butit's not going to be Anyway.
So it becomes a little bitsubjective.
(21:28):
So I think there may be someconstraints with EPAR, but I
think including it as a metricis very compelling in scientific
research.
Sam Humphrey (21:39):
So in this workshop, I love thinking about
this because I have been taughtthat, as Curt said, science
moves at a glacial pace and wepublish papers and build upon
each other's work and showevidence and it's sort of a slow
(21:59):
process all things considered.
But then at ASHS Conference2022, you held a workshop where
all these scientists who havebeen doing this work and have
spent their whole careerslooking at and trying to
understand plants and light andthe interactions they all got
(22:19):
together in a room to discuss.
So I find that so valuable.
Thank you for running thatworkshop.
I'm wondering if you could justdescribe simply the outcome of
that workshop discussion.
Erik Runkle (22:36):
Yeah.
So we had speakers where theygave basic overviews of the
different effects of far-redlight in the growth and
flowering process.
So the focus was very clearlyon far-red light.
And then we had a lot of timefor, I would say, debate and
discussion, although therewasn't a whole lot of debate,
(23:03):
wasn't a whole lot of debate,but people sharing their
thoughts and experiences andresearch with Far Red and the
merits of including Far Red inthe spectrum, in the spectrum
that we should be reporting inplant science.
And there were people it was avery well attended workshop a
lot of academics, a lot ofgraduate students and I was glad
to see also quite a few fromindustry.
(23:24):
And if you think about industry, you know they're creating
these LED fixtures and whetherwe consider far red in industry
being light that is useful forplants can really drive the
design of these differentfixtures for various reasons,
and so I was pleased to see thatthere were lighting companies
(23:46):
in particular that were at thisworkshop, and so I think we
walked away with a generalconsensus and agreement that far
red light, as we know, has abig role in the growth cycle of
plants and that we should bereporting it.
And there's still somequestions about whether, when
(24:10):
you design treatments, youshould have treatments that have
equal number of photons in thePAR region, or do you include
also far-red light?
So there's still different waysto do research.
One is not necessarily right orwrong.
It's more important that youclearly define your wave bands
in your treatments and the basisfor those treatments.
Curt Rom (24:33):
Again.
I find that very interesting,Dr.
Runkle.
One of the things abouthorticulture that our sciences
are both fundamental andtranslational.
They're applicable.
What do you see?
I've got two questions and youcan answer them in any order you
want.
What is the frontier of thisnew light science and what are
(24:55):
the new questions that areemerging from our discoveries?
That's one kind of thing I'dlike to address.
The other is so what you know,so what we now know this, but
how do we apply this and wheredoes this information fit?
Is it useful or is it just somesort of arcane knowledge?
Erik Runkle (25:17):
Well, I certainly hope it's not arcane knowledge.
So let me get to your firstquestion the frontiers of this
research.
And I don't have a real clearcrystal ball on that.
I think there are a lot ofquestions that we still have,
and some of those questions arelimited by LEDs and what peak
(25:38):
wavelengths are available forfar-right LEDs.
And so there's really one majortype of far-right LED.
It has an emission peak that isaround 730 nanometers.
I think there's a need for moreresearch where the peak
wavelengths are beyond that,both lower or higher.
I think we generally understandthat once you get beyond 750 or
(26:02):
760 nanometers, that there'sless or perhaps no utility of
those photons with respect togrowth or development of a plant
.
But I think we need tounderstand much better than just
subjectively choosing 750,because it's a round number, to
have a little more sciencebehind where that cutoff is for
(26:23):
the higher wavelength.
So I think that's one thingthat again is going to be
limited by technology.
However, I do think there aresome other approaches that we
can tackle that problem.
Also, I think questions aboutfar red and interactions with
other colors of light.
So far, red and blueinteractions are something that
(26:44):
I'm studying and very interestedin Blue and far red light in
some ways act antagonistically.
So blue light typicallysuppresses growth and elongation
.
Far red light typicallypromotes elongation.
And so then you have thisinteraction between the two, and
which one wins right, which onecan offset the other, and so
(27:08):
complexities that exist withother colors, as well as far-red
interaction, just with absolutenumber of photons, so light
quantity, and whether or not thefar-red light effects diminish
as light intensity increases ornot.
So those are, just off the topof my head, some of the areas
I'm personally interested in andI think there's still questions
(27:30):
about In terms of what doesthis all mean?
Of course, it means more for uswho are in plant science and
lighting research than manyothers, but I think, ultimately,
what we want is to createenvironments to grow plants
where we are maximizing growthwhile considering inputs.
(27:51):
And so if we're growing plantsin a greenhouse or indoors, in
cases where we are enriching thespectrum, for example, with
supplemental lighting, in caseswhere we are enriching the
spectrum, for example, withsupplemental lighting, the
question of delivering far-redlight or not can have an
economic impact on the crop.
(28:16):
It can affect the qualityattributes, potentially the
harvestable yield, things thatwill matter to the people who
are growing the plants andultimately to the consumer.
So we are understanding far-redand the effects and, of course,
not everything is good.
I mean there are sometrade-offs that exist with far
red is that you may get biggerleaves, for example, but it
could come at the consequence ofchanging the texture of a leaf.
If it's something you might eat, like a lettuce, it can
decrease the coloration of aleaf, so a leaf may not be as
(28:38):
dark green or as purple.
Decrease the coloration of aleaf, so a leaf may not be as
dark green or as purple with farred.
And so, understanding all ofthese effects of far red light,
knowing that there will be sometrade-offs, and keeping in mind
when we're growing horticulturalcrops, we want to make sure
that we're not resulting in aninferior product when it's sold
to consumers.
Curt Rom (28:57):
It makes sense why it started with NASA and their
technology.
Of course we want to feedpeople in space stations.
We want to go to Mars.
You have a very compellingargument that this will have an
impact on feeding 8 to 10billion people in the next 30
years if we do more protectedagriculture.
So it is very fundamental, butalso very applied.
(29:20):
It really has significantimpact because I do pay
attention to what my lettuce islike.
I have one more question.
It's not necessarily in yourarea, but just was curious.
You know when we think aboutplants absorbing light.
The primary antenna for lightabsorption has been a specific
(29:41):
kind of pigment.
In the case of photosynthesisit's chlorophyll for absorbing
PAR.
Have phytochemists identifiedpigment systems or other
chemical systems that areperceiving or absorbing these
other wavelengths of light?
I just don't understand.
Where is it chlorophyll?
Erik Runkle (30:01):
other wavelengths of ligh
Chlorophyll, yeah, so far-red,of course, can be useful in
photosynthetic reactions,especially lower-energy far-red,
so 700, 710 region.
But then there's phytochrome,which are the pigments in all
(30:23):
plants, at least light-grownplants, that perceive the ratio
of red and far-red light, andthere are several types of
phytochromes, and it's been veryextensively studied in
Arabidopsis, looking at mutantsof individual phytochromes and
understanding what happens whenthese plants lack one or more of
(30:44):
these phytochromes and howgrowth is different from a plant
that has the full phytochromecomponents.
One of the challenges thatexists, though, is that a lot of
this research is based onArabidopsis, which is a weed,
which is a plant with a veryshort crop cycle Seed to flower
(31:08):
is four weeks, for example.
So, knowing phytochromeresponses in Arabidopsis and, of
course, other plants too, thereare certainly some similarity,
but there are also somedifferences that can exist from
one crop to another phytochrome.
(31:28):
We will continue to improve ourunderstanding of the role of
phytochrome in mediating theseresponses to far red as well as
other colors of light, such asred light.
Sam Humphrey (31:48):
That's wonderful.
Thank you, Erik.
It's also interesting too,because phytochrome also absorbs
within blue wavelengths, right,and so there's so much research
.
Again, I was excited to hearthat you're interested in blue
and far red in combination inyour research.
So there's so many thingspeople could study, so many
(32:12):
different crops, so manydifferent wavelengths of light
and combinations like you weretalking about.
It's really exciting to seethis work evolve, combinations
like you were talking about.
It's really exciting to seethis work evolve If you were a
student and you listened to thispodcast and learned about how
the colors of light affectplants and if you wanted, to
(32:32):
learn more.
Curt Rom (32:32):
Where would you go?
Erik Runkle (32:35):
I mean the first impulse is to go to the internet
right and start typing inkeywords that are of most
interest to you.
So that could include far red,if that's what's exciting, or
blue colors or light qualityType in crops that might be of
particular interest to you, tosee if maybe there's a
combination of keywords, when astudy has been performed on that
(32:56):
, especially for horticulturalcrops, been performed on that,
especially for horticulturalcrops.
So that would be probably morefor the plant science side.
Go into Google Scholar andstart typing in keywords and
seeing what's the most, what arethe most recent papers that
have been published the lastfive years, for example.
So that's at least my go-to ofhow to find information is just
(33:17):
going to the internet and doinga search.
There are also ways you couldlearn about the people who are
doing this research and thereare quite a few in the United
States as well as several other,many other countries to learn
what their active researchprograms are studying.
So that's the scientific side.
(33:40):
If people are more interestedon the application side, there
are a lot of grower articles outthere that I and many of my
colleagues have written aboutlight and plants and
specifically about far red, forthose who might be interested,
or other colors of light, and sothat can be information that's
a little more digestible, rightPapers or articles that have
(34:08):
been written for not ascientific audience but maybe a
more professional audience or anindustry audience.
So I guess that would be myapproach.
I actually, sam, I'd beinterested to see I mean, you're
, you're interested in this areawhat?
What are ways that you try tofind information and seek more
information about like quality?
Sam Humphrey (34:27):
I'm a little bit biased, Dr.
Runkle.
Um, I would go to ashsorg andfind the journals tab where ASHS
has three journals where theypublish publications relevant to
this, and I would search thatspecifically because I know
those papers are of high qualityand I know you've published in
those journals as well.
(34:47):
I would say sometimes you canfind scientists who make amazing
extension materials, like Dr.
Bugbee, as you mentionedearlier in this interview.
He hasa website where hepublishes some of his lectures
that he's given to classes, andyou can watch some of those
online lectures and abstractsand things from previous ASHS
(35:12):
conferences.
So that's where I would go, inaddition to what you described.
Curt Rom (35:19):
That's where I would go in addition to what you
described, speaking about ourjournals with this kind of new
information and newconsiderations?
Are you visiting with editorsand reviewers that, instead of
just saying I measured PAR, theyshould start reporting the
wavelengths that they measure,the technology that was used to
(35:39):
measure that?
Erik Runkle (35:39):
I mean, I've got a bunch of PAR sensors that aren't
going to measure what I mightneed to measure now you know
that that comes up when I'mreviewing papers that are
focused on light quality, and soif they're studying that, then
I think it's an you know, it'san absolute expectation that
(36:00):
they have measured the lightspectrum and are reporting it,
and so they would include blue,green, red and far red light,
and even if they're not studyingfar red, it would be important
to know the lamp type or some ofthe characteristics so that if
we wanted to find thatinformation ourselves, the
information was available.
So if we were to review a paper,whether it's for an ASHS
(36:22):
journal or another, that's theopportunity we have to provide
feedback, and if we feel verystrongly about something, we can
write a short justification formaybe a fundamental flaw,
that's sent to the editor sothat they know that this is a
pretty important aspect that haseither not been reported or
perhaps even overlooked In termsof you know how we try to move
(36:48):
this forward with ePAR.
I think you know we go to a lotof the same meetings, ASHS
meetings.
We see a lot of our colleaguesand talk about these things in
their papers and presentationsfocused on PAR, and there we can
emphasize the importance ofreporting PAR and ePAR when it's
relevant, as well as in papers.
(37:10):
You know we can talk about PARand ePAR in the same breath, and
when we have opportunities totalk about PAR, whether it's
with colleagues in academia,graduate students or industry,
we can talk about FAR-RED, Someof the advantages and
disadvantages, and, when itcomes to reporting, when and
(37:30):
when it may not matter- Well,this has been very enlightening
if I can say that with astraight face.
Curt Rom (37:37):
You know it's been informative and fun.
If I can say that with astraight face, you know it's
been informative and fun.
Like I've said, I became ahorticulture physiologist
because I heard an interestinglecture on light in an
undergraduate physiology class,and so is this, you know, the
kind of additional step for meunderstanding and learning about
the impact of light, and I cansee it.
(37:59):
It's opened my eyes for real.
I understand light a little bitbetter.
Sam, what do you think?
Sam Humphrey (38:09):
I really love this conversation.
I love talking about light ingeneral, so it's not a surprise,
but hearing from one of thescientists that's at the
forefront and who is helpingdrive this conversation,
promoting good science andtrying to move the needle
(38:29):
forward with our understandingof how plants respond to light.
It's just wonderful to talkwith you, Dr.
Runkle.
Curt Rom (38:47):
The ASHS podcast Plants, People, Science is made
possible by member dues andvolunteerism.
Please go to ashs.
org to learn more.
If you're not already a memberof the ASHS, we invite you to
join.
ASHS is a not-for-profit andyour donations are tax
deductible.
Sam Humphrey (39:05):
This episode was hosted by Samson Humphrey and
Curt Rom.
Special thanks to our audioengineer, Andrew Sheldorf, our
research specialists Lena Wilsonand Andrew Sheldorf, our ASHS
support team, Sara Powell andSally Murphy, and our musician
John Clark.
Thanks for listening.
Thank you.
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