# Green light bad for Paphs?



## polyantha (Sep 14, 2013)

I am currently looking for grow light bulbs for my paphs. Depending on which colour temperature the plants need I found this:

http://pcp.oxfordjournals.org/content/43/6/639.long

"Blue light-specific stomatal opening has a number of distinct characteristics. The action spectrum shows a maximum at 450 nm and subsidiary peaks at 420 and 470 nm (Karlsson 1986b). Low fluence rates of blue light (1–10 µmol m–2 s–1) are effective in stimulating opening (Schwartz and Zeiger 1984). Red light enhances the amount of stomatal opening resulting from a given dose of blue light (Karlsson 1986a). Most recently, blue light-stimulated opening has been found to be reversible by green light (Frechilla et al. 2000). The stomatal response to pulses of blue and green light is determined by the order of the pulses, in a manner analogous to the red/far red reversibility of phytochrome responses. The action spectrum for the green reversal resembles the three-peaked action spectrum for blue light-stimulated opening, red-shifted by about 90 nm (Frechilla et al. 2000)."

"A detailed study of the dose-response relationship of red light-stimulated stomatal opening in Paphiopedilum showed that the lowest fluence rate of red light tested, 10 µmol m–2 s–1, stimulated the largest apertures, whereas increasingly higher fluence rates gave progressively smaller responses. Opening was negligible when red light was applied at 120 µmol m–2 s–1 (Fig. 3). "

So blue has an absorption maximum between 420 and 470 nm.
The more blue the more opening
The more green the less opening
Red does have a positive effect, but the more red the less reaction

Not an easy text for me, please correct me if i am wrong 

I need all the infos I can get to set up a good lighting system for my plants. After reading this text I would say that the lamps should have much blue (420-470nm), a little red (630-700) and as few green as possible right?


----------



## polyantha (Sep 14, 2013)

Green light reversal of blue light-stimulated stomatal opening in Paphiopedilum. Aperture values given are for: before light treatment (Initial); after 3 h illumination with continuous 10 µmol m–2 s–1 green light (Green); 10 µmol m–2 s–1 green and 5 µmol m–2 s–1 blue light (2 : 1); 5 µmol m–2 s–1 green and 5 µmol m–2 s–1 blue light (1 : 1); and 5 µmol m–2 s–1 blue light (Blue). Results are the average of three experiments ± SE of the measurement. 






Effect of increasing fluence rates of red light on stomatal aperture in Paphiopedilum. Change in aperture from initial values after a 3 h illumination are shown for four fluence rates of red light. Aperture change after a 3 h illumination with 5 µmol m–2 s–1 blue light (Blue) is shown for comparison. Results are the average of four experiments 






Effect of far red light on the green reversal of blue light-stimulated opening in Paphiopedilum. Aperture values given are for: before light treatment (Initial); after 3 h illumination with continuous 5 µmol m–2 s–1 blue light plus 10 µmol m–2 s–1 green light plus 180 µmol m–2 s–1 far red light (B-G-FR); 5 µmol m–2 s–1 blue light plus 10 µmol m–2 s–1 green light (B-G); 5 µmol m–2 s–1 blue light (Blue), or 5 µmol m–2 s–1 blue light plus 180 µmol m–2 s–1 far red light (Blue-FR). Results are the average of five experiments ± SE of the measurement.


----------



## naoki (Sep 14, 2013)

Nice find! I've been wondering the adaptation to different spectrum of light (motivated from optimal LED spectrum), so I should take a look at this paper. Probably you know this, but there are several pathways of stomatal control, and blue vs green is just one of them. Blue activation makes sense, but I've never understood why green light is used as the reversal cue. Other well studied pathway involves Abscisic acid (ABA), which is used as a SOS signal by dehydrating cells.

With regard to minimizing green light, opening stomata is not always a good thing. Plants need to balance loss of water via transpiration with the cost-benefit of photosynthesis vs photorespiration (rubisco binding to O2 instead of CO2, and this wasteful process counteract carbon assimilation). So depending on the environment (light, RH, water potential at the root level), plants need to open and close stomata appropriately.


----------



## naoki (Sep 15, 2013)

Pretty interesting, but they don't quite explain adaptive significance of this response (or it wasn't clear to me).

This paper is about what kind of sensors are used to sense light. Again, light is just one of many factors to control the guard-cell opening, but plants do need to gauge the quantity and quality of light. Paphs are used because they have guard cell with undeveloped chloroplast (a pretty unique trait).

From my quick read, it is opposite from what you mentioned. Paphs open stomata more than other plants under the existence of green light. Green light generally reverse the effect of blue light in other plants. But this reversal effect was weaker in Paph. This is because in Paph, there is an additional sensor (probably phytochrome) in addition to blue light sensor, which promote stomata opening. This additional sensor enhances the opening of stomata by green light. So there are two things going on. The effect of the blue light sensor is countered by green light. But green light by itself can promote opening. Therefore, in other plants, green light can completely reverse the opening effect of blue light, but in paphs, stomata remains open (more closed than blue light only). Further, this opening effect of green light is countered by far red light. The green light opening effect is smaller than blue light effect.

One additional thing is that strong red light (in existence of blue light) causes closure of stomata. The authors speculate that paphs are shade plants, so when there are too much direct sun light (indicated by high red/far red ratio), they need to close stomata to reduce transpiration.

It's a complicated system, but I wonder if this suggests that LED with higher blue to red ratio LED than other plants under cultivation where water isn't limited much. But I don't know enough about this topic to make practical conclusion from this paper.

Note that these stomatal response seems to be talking about the regulation at the low intensity of light (maybe dusk and dawn?). So, I'm not sure if it is relevant during the day time.


----------



## polyantha (Sep 15, 2013)

I guess you are right. Green does not reverse the blue light reaction completely, just affecting it negatively right? But I wonder if one should avoid the far red spectrum then to avoid closure of stomata?

In "THE PHOTOBIOLOGY OF Paphiopedilum STOMATA: OPENING UNDER BLUE BUT NOT RED LIGHT" I found that:

In isolation, Paphiopedilum stomata appear to rely on a blue light photosystem for their responses to light and fail to open under red light because of their lack of guard cell chloroplasts.

This means that Paphs don't use red light? When the stomata stay closed the plant is not producing any engergy from the red light.


----------



## naoki (Sep 15, 2013)

Yes, green doesn't reverse the blue light reaction completely in Paphs (but it does in other plants).

I'm not sure if it is better to avoid FR. From the last figure in your post, it seems to require lots of FR (relative to G) to reverse the opening effect of green. Phytochrome is involved in many physiology. In some plants, reduction of FR (relative to R) prevents etiolation, or it is important to sense the season (short vs long night). My LED grow light doesn't have any FR (but some marijuana growers seem to think that FR is important).

For photosynthesis, I'm sure that paphs use red light. My understanding is that Paphs don't seem to use red light to detect whether it is receiving light or not. Actually, 2nd fig in your post is showing that low level of red light can open stigma, but higher level of red light doesn't have this effect. They are speculating that shade plants may have this rather weird reaction to avoid loss of water when sun is directly hitting the leaves.

But this experiment is isolating the effect of light on stomatal opening from other factors. So my speculation is that in real life, this mechanism may be only important to determine when they wake up and when they go to sleep. During the day, other stomatal control may dominate (concentration of CO2, ABA, moisture level etc).


----------

