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Re: Red light, green light

> Date: Wed, 23 Jul 1997 10:03:02 -0600
> From: George Booth <booth at hpmtlgb1_lvld.hp.com>
> Subject: Red light, green light
> Pardon the long winded rambling, but I am feeling expressive today.
> I was responding to a rec.aq.fw.plants posting yesterday when a stray
> neutron entered my head, rattled around for awhile and sparked an
> idea.

Have you tried making a hat out of aluminum foil?  :-)

> The poster was complaining about the supposed marketing hype regarding 
> Amano's "NA" [Nature Aquarium] bulbs, to whit, that green wavelengths
> are beneficial to plant growth.   
> We all "know" that only red and blue wavelengths are of any real use,
> based on ancient studies of photosynthetic algae, which naturally
> apply to anything even remotely plant-like. [note my sarcasm, here]  

> It was further pointed out that bulbs emitting strong green
> wavelengths would actually make sick plants look healthy, thus
> deceiving the tri-phosphor cognoscente into thinking our plants are
> healthy and vibrant when in actuality they are rotting before our
> very eyes. 

I've got a compact fluorescent in my kitchen ceiling fixture that makes
the houseplants and salad veggies look truly lush when it's the only 
source of light.  It looks somewhat yellowish - it probably has lots of
green in it.

> "Uh-huh", thought I, "well, well, what about plants with RED leaves?
> I guess they aren't reflecting green light, are they?  They might
> actually be refecting God's Own red light!  They might even THRIVE
> with strong green light!".  You know, plants like Rotala spp..
> Alternanthera spp., Ammania spp., Ludwigia spp., etc.  
> So, any comments?  I mean about green wavelengths being useful to
> plants with red leaves, not about my ponderous prose. 

Orange and yellow pigments (carotenoids) are involved in the photosynthetic
process in both algae and higher plants.  I don't know whether there is any
evidence that it's necessary for these pigments to absorb photons from 
sunlight for anything in particular to happen.

Red plants are another story.  Plants often produce anthocyanins (red/blue/
purple pigments) in their leaves as a response to excessive light.  These
pigments intercept some of the photosynthetically active photons before they
can reach the chloroplasts.  However, mutants that produce lots of anthocyanin
without light stress are pretty common in horticulture.  People have selected
for these colored forms.  Aren't many of the red aquatic plants mutants not
often found in nature?  Such mutants tend to need more light than the normal
green forms, for the obvious reasons.

While we are theorizing here, I'd like to wave my hands a bit.  You know
how crypts often have red-purple colour under the leaves?  How about the
theory that this tactic helps these low-light plants by intercepting any
red or blue photons that make it through the leaf, and reflecting them
back for another go, sort of like the stunt cats use to see in the (almost)
dark by cleverly having a reflective layer behind their retinas to give
the photons a second chance to impinge?  (Hmmmm... now that I think of
it, the cats' eyes reflect GREEN...wow...cosmic! :-))

> George, on the verge of a new marketing campaign 

I hope the real plant scientists out there will correct me where I'm wrong 
in any of the above.

Beverly, starting to get carpal tunnel from handwaving