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Re: Red light, green light

"Light and Plant Life" by Whatley and Whatley (1980) is a smallish
volume on how plants use light.  I've copied a few excerpts from it. 

   "There are three main groups of pigments associated with the principle 
photoresponses in plants;  (1) the chlorophylls, concerned with 
photosynthesis (2) phytochrome, concerned with with some morphogenetic 
changes, daylength perception and probably also with the phasing of the 
daily rythms affecting some plant movements and (3) beta-carotene or 
flavins, concerned with phototropism."

Each of these groups of pigments consists of more than one pigment, each
pigment has a different adsorption spectrum, and the "action spectrum" -
which measures the response of the plant (or part of a plant), rather than
the response of the chemical - is different from the adsorption spectrum.
The difference is because the pigments are found with proteins that modify
their response. 

Typically "green" light is near the minimum for most of the photosensitive
plant processes.  That doesn't mean the plants don't use it.  Again from 
Whately and Whatley:

"...the action spectrum for photosynthesis shows that green light is 
nevertheless effective, though the main peaks are in the red and blue.  
This appears to be due to adsorption of light by the carotenoids, which 
normally accompany the chlorophylls in the chloroplast membranes ... This 
energy transfer has important implications for the successful growth of 
understorey plants in forests, which are apparently at less disadvantage 
than might be expected from the colour of the filtered light."

Light in a forest understory is strongly green.

Someone in an earlier post said that aquatic plants are classified as 
shade plants, so I guess they might have some characteristics in common 
with forest understory plants.

Roger Miller