# Plant Light Receptors



## Hobbes (Mar 21, 2010)

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I'm going to use this thread to store info on plant light receptors and for discussion about plant light receptors and subjects pertaining to, but perhaps not specifically about, plant light receptors. Open thread, post what info you come across and have any discussion about light receptors you like.

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*Illuminating light-receptors in plants*

*The mystery about plants' internal 'light switches' is slowly being unravelled, thanks to theoretical chemists in Sweden.Phytochromes in plants are light receptors that are responsible for releasing chemicals that trigger processes in cells like germination or flowering. They work when exposed to red light with a specific wavelength. Two different phytochrome forms exist: one is active and one inactive. Switching between them depends on the light?s wavelength.


Bo Durbeej at Uppsala University and colleagues have used quantum chemical techniques to decipher what happens when the different phytochromes isomerise. They think that the initial step is photochemical, and subsequent isomerisations are heat driven. So far, Durbeej has looked at a single phytochrome in the gas phase, which in itself is a quantum chemical breakthrough, but the hope is to one day understand what happens when the phytochromes interact with surrounding proteins.* 


_Katharine Sanderson_


_http://www.rsc.org/chemistryworld/Issues/2004/November/illuminatinglight.asp_


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## Hobbes (Mar 21, 2010)

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*Phototropism* is directional growth in which the direction of growth is determined by the direction of the light source. In other words, it is the growth and response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light have a chemical called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the farthest side from the light. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is a *positive phototropism*, while growth away from light is called *negative phototropism* (or *Skototropism*). Most plant shoots exhibit positive phototropism, while roots usually exhibit negative phototropism, although gravitropism may play a larger role in root behavior and growth. Some vine shoot tips exhibit negative phototropism, which allows them to grow towards dark, solid objects and climb them.

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Plants absorb light with the help of chlorophyll that is built into the thylakoids' membranes. This chlorophyll is green in colour and absorbs red and blue light. They do not and are incapable of absorbing green light. It is this fact, the inability to absorb green light, that makes the leaves of plants and chlorophyll appear green to the human eye. Plants require light energy for the process of Photosynthesis by which they convert this light energy to chemical energy. This energy is stored by plants in bonds of sugar. The process of converting light energy into a food source is unique to plants and some algae. No other type of organisms on earth can manufacture its own food. The chemical reaction that takes place during this process is represented as 6CO2 + 6H2O (+ light energy) &#8594; C6H12O6 + 6O2. 

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*BASIC PHOTOMORPHOGENESIS*



James Shinkle 

Department of Biology, Trinity University
San Antonio, TX 78212-7200
[email protected] 

*Introduction* 

Big sessile organisms like plants and fungi and small organisms whose motility can't move them that far, like bacteria and protists, have no option but to function in the environment they are found in. For photosynthetic organisms it has been adaptive for them to develop mechanisms to sense their light environment, and adjust their form and metabolism to optimize their performance under their local conditions. Since light environments change, these organisms have also developed the ability to continuously adjust their function to current conditions. Taken together these responses to light constitute the phenomenon known as photomorphogenesis. 

The definition of photomorphogenesis, as applied in this module, is any change in form or function of an organism occurring in response to changes in the light environment. Photomorphogenesis is often defined as light-regulated plant development (Figure 1), but there are also changes in morphology and/or cell structure and function, which occur as transient acclimatizations to a changing environment, which are also light regulated. Particularly if this more inclusive definition is used, photomorphogenesis is a process common to organisms well beyond the plant kingdom. While there may be only a few examples of photomorphogenesis in the animal kingdom, it is a common feature of development in fungi, protists, and bacteria, as well as plants. While this module will focus on what is known from studies of plant photomorphogenesis, there will be selected examples from other kingdoms. 






*Figure 1.* Photomorphogenesis as a morphological and as a cellular process. The left photos show the change in form of an _Arabidopsis thaliana_ seedling grown in darkness (top) or in white light. The right hand illustration shows the change in chloroplast structure and diagrams the progress of light signals through two receptor systems, cryptochrome and phytochrome. Adapted from Biochemistry and Molecular Biology of Plants, (c) American Society of Plant Biologists, with permission.​ *The Information Content Of Light* 

Photomorphogenesis is an organismal response to information present in the light environment. There is information concerning: simple presence of light, light direction, light intensity, light duration, spectral quality and polarization (see _Mougeotia_: A Chloroplast with a Twist, for a description of the last phenomenon). Studies have demonstrated photomorphogenic effects of all of these parameters of the light environment in diverse organisms. However, it must be acknowledged that the responses to polarization were observed in laboratory conditions that may not have any parallel in the natural light environment. It should also be noted that the earliest responses to light exhibited by germinating seedlings are initiated by the mere presence (or absence) of light, information of the simplest sort possible. 


*Diversity Of Processes Of Photomorphogenesis* 

It would be impossible to provide a comprehensive catalog of photomorphogenic processes, and it would not serve any particularly useful purpose. The brief list below is an illustration of the diversity of organisms and processes falling within the realm of photomorphogenesis. All of the processes listed entail the coordinated regulation of several to many developmental events at the cellular and (where relevant) organism level. 

http://www.photobiology.info/Shinkle.html

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## Hobbes (Mar 21, 2010)

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*Capturing light energy*


*A reaction centre is laid out in such a way that it captures the energy of a photon using pigment molecules and turns it into a usable form. Once the light energy has been absorbed directly by the pigment molecules, or passed to them by resonance transfer from surrounding antenna pigments, they release two electrons into an electron transport chain.


Light is made up of small bundles of energy called * *photons. If a photon with the right amount of energy hits an electron it will raise the electron to a higher energy level.[2] Electrons are most stable at their lowest energy level, what is also called its ground state. In this state the electron is in the orbit that has the least amount of energy.[3] Electrons in higher energy levels can return to ground state in a manner analogous to a ball falling down a staircase. In doing so they release energy. This is the process which is exploited by a photosynthetic reaction centre.


When an electron rises to a higher energy level this increases the * *reduction potentialpheophytin, quinone, plastoquinone, cytochrome bf, and ferredoxin that ultimately result in the reduced molecule NADPH. The passage of the electron through the electron transport chain also results in the pumping of protons (hydrogen ions) from the chloroplast's stroma into the lumenthylakoid membrane that can be used to synthesise ATP using ATP synthase. 

Both the ATP and NADPH are used in the Calvin cycle to fix carbon dioxide into triose sugars**of the molecule that the electron resides in. This means the molecule has a greater tendency to donate electrons, the key to the conversion of light energy to chemical energy. In green plants, the electron transport chain that follows has many electron acceptors including resulting in a proton gradient across the thylakoid membrane that can be used to synthesise ATP using ATP synthase. Both the ATP and NADPH are used in the Calvin cycle to fix carbon dioxide into triose sugars.* 

http://en.wikipedia.org/wiki/Photosynthetic_reaction_centre

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## Hobbes (Apr 27, 2010)

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I came across this great article on Photoperiodism and wavelengths in the far red (~730nm). Photoperiodism is basically flowering with a change in day/night cycle. They're also finding that wavelength effects flowering, 660nm by itself may slow flowering but if combined with 730nm it will help.

Great article.

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Photoperiodism.html

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I'm going to make my own light bar using Breadboards (Protoboard - plug and play, no soldering). I tried buying a few UFOs but the companies that sell them do not seem legit. I've been playing with the idea of a remote ballast to reduce weight on the Light Rail but I haven't got that far in the design process yet.

I'm concerned about heat with breadboards (because I don't know much about them yet) but I may want to switch my LEDs around some and breadboards will be great for a prototype.

http://www.sparkfun.com/commerce/product_info.php?products_id=8812

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## T.H.Cammo (May 2, 2010)

Hobbes said:


> .
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> They're also finding that wavelength effects flowering, 660nm by itself may slow flowering but if combined with 730nm it will help.


After reading your thread and clicking on some of your sources, I must say, I am favorably impressed. Perhaps there is some hope for the "Advanced Techniques" Forum after all!

Yeah! Combining "Normal" red spectrum (660nm, or so) with far red spectrum (730nm, or so), is called the "Emerson Effect". Just Google _emerson effect_ and you should get several articles that will explain it in "everyday English". From what I understand, "useless" Halogen bulbs are, indeed, a great source of "far red" light (so they really are good for something!). As I recall, the "far red" booster lights only need to be on for the the last few minutes (15-20) of the photoperiod - correct me if I'm wrong, it's been many moons since I read about this stuff.

I have a question for you, if you don't mind. You seem to have done a great deal of research on "Light", specifically on photons and light receptors (and how they actually function). As I recall, the photon gets "swallowed" by the indevidual light receptor, then, the light receptor (immediately) goes "off line" for a brief period of time, appearantly to "process" the photon. If I understand this process correctly - it sounds very similar to the way a "Venus Flytrap" plant works (except for the time frame involved!). The actual "Time-Frame" is what my question is about. At the time I did my research, there was no reliable way of knowing just how long these light receptors stayed "shut down" after a meal of a photon. A milli-second, a few seconds? There was no answer to be had! So, my question is, have you come across this subject matter and do you know how long the light receptors remain "off-line" after "eating" a photon?


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## Hobbes (May 2, 2010)

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*"have you come across this subject matter and do you know how long the light receptors remain "off-line" after "eating" a photon?"*

I haven't yet Cammo, I was conceptualizing the situation incorrectly and now I'll research the recptors going "off line".

I was thinking of each light receptor as a tiny bucket and each photon as a tiny drop of water. The light receptor buckets have a hole in the bottom and lots of photons fill the bucket and the bucket slowly drips out the photons from the bottom. My questions were - how long do the buckets have photons in them before they've completely drained and are empty, which begs the question - how big are the buckets so ...

How much light intensity / time is needed before the light receptors shut down and go off line? How long will they stay off line? If we don't saturate the light receptors with enough photons to shut it down how long can we leave it to drain before it requires more photons for good/optimal flowering?

Excellent concept Cammo, basically photons hitting the light receptor after it's saturated are probably wasted or used at an inefficient rate. I'll find out as much info as I can and post it here.

As well it makes me think about aggressive flowering and shutting down light reflectors - possibly intense light is needed to shut down the light receptors which may send signals to the rest of the plant to pump out big buds. - "Hey Buds its the Light Receptors! There are lots of photons in intense bursts probably means a good growing environment, grow as big as you can!" - Maybe not just getting the photons, but getting them in intense bursts which causes the light receptors to shut down and to send signals to the rest of the plant. Possibly, maybe, might ... something to look into.

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*"** As I recall, the "far red" booster lights only need to be on for the the last few minutes (15-20) of the photoperiod"*

I believe you're correct. This is a great chart, shows the effects of bursts of 660 nm and 730 nm light during the dark period for a flowering plant. 

Chart Summary: If a plant is hit with only 660 nm light during the dark it will not flower, but if hit with 660 nm during the dark, then 730 nm during the dark it will still flower - converting Pdr back to Pr.
 





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*"**Combining "Normal" red spectrum (660nm, or so) with far red spectrum (730nm, or so), is called the "Emerson Effect""*

I didn't know that, thanks!

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(for people new to the Emmerson Effect)


 *Phytochrome*

Phytochrome is a homodimer: two identical protein molecules each conjugated to a light-absorbing molecule (compare rhodopsin). 

Plants make 5 phytochromes: *PhyA*, *PhyB*, as well as C, D, and E.
There is some redundancy in function of the different  phytochromes but there also seem to be functions that are unique to one or another. The phytochromes also differ in their absorption spectrum; that is, which wavelengths (e.g., red vs. far-red) they absorb best.

Phytochromes exist in two interconvertible forms 

*PR* because it absorbs red (R; *660 nm*) light;
*PFR* because it absorbs far red (FR; *730 nm*) light.
These are the relationships: 

Absorption of red light by *PR* converts it into *PFR*.
Absorption of far red light by *PFR* converts it into *PR*.
In the dark, *PFR* spontaneously converts back to *PR*.







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I'm interested in playing with the far red spectrum, seeing if applying different intensities at different times of the light period will make the plants flower more aggressively. Or if too much far red light through the mid day will retard flowering - perhaps following the hourglass curve of the far red's intensity during the day is what's needed rather than a light with constant far red light intensity. Maybe very intense 730 just before lights out to kick start the conversion of Pdr to Pr as you suggested with the 15 minutes before lights out.

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## T.H.Cammo (May 2, 2010)

Okay! First off, a great big fat rhetorical question! How great is it to have someone to actually discuss a different point of view - rather than get into a "shit flinging" argument? You sir, are a gentleman and a scholar!



Hobbes said:


> . - - - -
> I haven't yet Cammo, I was conceptualizing the situation incorrectly and now I'll research the recptors going "off line".
> 
> I was thinking of each light receptor as a tiny bucket and each photon as a tiny drop of water. The light receptor buckets have a hole in the bottom and lots of photons fill the bucket and the bucket slowly drips out the photons from the bottom.
> ...


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## Brainy (May 2, 2010)

Great read guys. This subject of light receptors effects me because I am using a light mover and would like to know a way to figure the delay time. Just trying to be more green!


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## T.H.Cammo (May 2, 2010)

Brainy said:


> Great read guys. This subject of light receptors effects me because I am using a light mover and would like to know a way to figure the delay time. Just trying to be more green!


Ah! I see we're starting to draw a wider audience - Kool! I can't really say from personal experience, but I have thrown the question out there! Most responders said a slower cycle is more preferable, something like 15 minutes - does that make sense?

I've never used a light mover, but I'm working on a prototype "turntable floor system" (something like a motorized Lazy Susan), that will slowly rotate my plants around multiple, stationary, lights. So I need to figure out what is an appropriate R.P.M. Okay, you guys - any ideas? I've been guessing about 5-20 minutes per revolution (1/5th - 1/20th R.P.M.).


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## Hobbes (Jun 16, 2010)

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TH my light mover takes about a minute or two to cycle up and down an 8 foot garden - one revolution per 5 minutes with several lights would be fine.

I believe that you would have an easier time with a rotating light mover than rotating floor, less weight and the plants don't move when you want to work on them.







http://www.4hydro.com/lighting/solarRevolution.asp

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## riddleme (Jun 16, 2010)

Great post!

I will be adding far infrared light to my next grow, my research indicates that it is the first and last thing the plant sees as the sun rises and sets, I will be starting the IR 15 min before lights on and running 15 min after lights out, as my research showed this affect internode spacing and growth

I must also admit that my experiment is more about heat than light


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## phyzix (Dec 19, 2010)

Point of clarification here...

If a photon isn't absorbed by a light receptor on a leaf (because it is currently processing or the photon misses), wont it simply carry right though and onto the next, lower leaf? By lower, I mean farther from the light than the first leaf and within the trail of the photon. 

So, if all the receptors on the top leaf are busy processing because of an abundance of light, more photons would simply penetrate to the lower leaves to be processed there.

It seems like this would have negligible impact to me, but I could be very wrong 

Sorry for bumping an old thread, but I know you guys still post here.


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## canefan (Dec 20, 2010)

Great read and info guys thank you this goes into my library for further diegestion....lol. Just having my first cup of coffee and pipe, it is like my 8 o'clock bio class in college, I need more time to understand fully....lol. This is just in time as I am finally getting some lights next month and gives me a chance to study more.
Thanks again and Merry Christmas


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## T.H.Cammo (Jan 3, 2011)

phyzix said:


> Point of clarification here...
> 
> If a photon isn't absorbed by a light receptor on a leaf (because it is currently processing or the photon misses), wont it simply carry right though and onto the next, lower leaf? By lower, I mean farther from the light than the first leaf and within the trail of the photon.
> 
> ...


The short answer to your question is yes! If the "Top layer" of leaves is "busy", then the remaining (diminished amount) of light must find it's way down, deeper, into the canopy; to try and find an available light receptor. With "good old" Sunlight, this is no problem - with artificial lights, not so much! 

Individual photons are kind of "wimpie" and the subject of light penetration may be a little controvercial - at least it's not unanimousely aggreed on. Leaves block more light than they transmit, so this process isn't very efficient. Some say that "Brute Horsepower" is the best way (using more powerful lights, like 1,000 watt HID'S). I prefer the "Multiple Light Source" aproach (using four, seperate, 250 watt HID"s - for the same situation). My reasoning is that - primary light, comming from several different directions, is better able to penetrate the "Shade Cover" by slipping between the leaves, instead of (a single source) having to penetrate through them. In addition, four lights covering the same area, means the light only has to travel 1/2 as far (side to side) - yielding 4x the usable light, in accordance with the "Inverse Square law" (for the propigation of light).


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## lbezphil2005 (Jan 31, 2011)

Excellent info, Cammo, Hobbes, and phyzix!!! Talk about a deep subject!!


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## RawBudzski (Jan 31, 2011)

HOBBES! MY secret LOVER... I now have 2 600w Lights. I also MAY GET THE LIGHT MOVER YOU SO OFTEN SPEAK OF> can it run 2 LIGHTS? would that be smart? to maybe have mh/hps both running on a track?


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## RawBudzski (Jan 31, 2011)

You may refer to me as Baruch Spinoza. Give me info. or a map to your mind


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## phyzix (Mar 7, 2011)

RawBudzski said:


> HOBBES! MY secret LOVER... I now have 2 600w Lights. I also MAY GET THE LIGHT MOVER YOU SO OFTEN SPEAK OF> can it run 2 LIGHTS? would that be smart? to maybe have mh/hps both running on a track?


Depending on your particular setup, the effectiveness of a light mover with multiple lights is generally limited. This is because having two sources of light already provides far better coverage than a single light. Moving two lights may allow for more square footage to grow in though, so don't let me discourage you.


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## Hobbes (Mar 18, 2011)

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Light movers are also beneficial to reduce light poisoning - constant intense light destroys the chloroplast, the solar panels of plants.

A cruel irony is that 12 hours of constant light from an HID actually reduces the percentage of light that the plants can absorb and convert to chemical energy to produce buds. A Light Rail not only doubles the space of our gardens it also gives the chloroplasts down time to distribute the chemical energy.

Plants evolved with a moving light source, clouds, shade from its own leaves as well as cover plants. We want to give the plant enough light so it produces a chemical signal telling the rest of the plant that there is lots of intense light, then we want the light to move directly over the next plant to do the same.

I'm able to harvest 12 gallons of cured bud (25% of cut weight) with a 600 watt light in an 8' x 3' grow cage, this is close to 5 grams per watt with an HPS. There is much more possible than conventional wisdom allows, check out the Grow Lab thread linked below for a chronological pictorial and the Weed Science link to a free ebook download.

Raw if I would suggest a single light per light rail and two grow cages if you want to run two lights. Being able to work on all of my plants without reaching over makes gardening much easier.

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## OpSec420 (Apr 8, 2011)

Concerning light movers: something I have not seen are light movers for vertical bulbs in vertical grows. Any comments on that? My head is stuck on this idea of three steps, three plants per step, each section of three steps comprising a wall and 6 walls forming a hexagon shaped room. Likewise staggered diagonal to each step a vertical, moving 1000w hid. The HID's would be spaced every other wall and timed to transverse a wall in three minutes. So each section would have three minutes of intense light, each step receiving intense light from three directions; followed by 3 minutes of less intense light (as the other HID's would be making their journey across adjacent walls, light moving towards the wall from the wall behind it, and light moving away from the section 'in front of' it. 

The idea being maximum canopy penetration as well as not blasting the plants with constant high intensity light; constantly (and consistently) shifting shadows. And if I have my math right, the wattage and lumens are correct for this number of plants. 

I have been studying various techinques and theories for awhile now, and though I won't pretend to be any kind of expert, I have put some thought into this. 

Please critique, thank you 

btw. I do not mind twisting and bending as I work, and if this is practical in grow terms I would work on making the system more ergonomical.


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