Subject: Help - Light spectrum and phototropism

From: [email-masked] (steve )
Date: Tue, 16 Apr 1996 11:58:42 GMT

A problem!
Do plants respond to all wavelengths of light, or is there one in
particular they respond to more than others?
 If so, which, and why?
Thanks
Jamie

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From: [email-masked] (Stephen M Gomez)
Date: Tue, 16 Apr 1996 18:28:13 -0800

> particular they respond to more than others?

Blue is best.  At least if you want to see plants bend towards the light.

Some folx have found a membrane bound flavinoid-binding protein that is
postulated to be the blue light receptor (Short etal. 1992 Photochem.
Photobiol. v55 p773)

The other possible source of the blue light photoreceptor is zeaxanthin in
the light harvesting complex of the chloroplast (Quinones and Zeiger 1994
Science v264 p558).

Corn and oat coleoptiles are a really good example of blue light phototropism.
Let them sprout in the dark and grow in the dark for a few days.  then put
them in blue light (to the side) and in a day or two the coleoptiles will
be pointing towards the light.  Not w/ red/orange/yellow.  A little w/
green.

steve

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From: [email-masked] (Marco_Bleeker)
Date: 17 Apr 1996 22:36:13 GMT

>Blue is best.  At least if you want to see plants bend towards the light.

Blue, and red. 

>be pointing towards the light.  Not w/ red/orange/yellow.  A little w/

Hey, as a student, more then 20 years ago, I remember sitting in a
dark room with oat seeds (and a collegue :-), but we were
experimenting with RED light. They responded strongly to FAR-RED
(wavelength 680 - 700 nm). If I remember right ?!!

But this phototropy has nothing to do with photosynthesis. Here are
blue (420 - 470) and normal red (640 - 670) most effective: absorption
peaks of Chlorophyl a and b.

Bye, marco

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From: [email-masked] (Rglabra)
Date: 25 Apr 1996 18:52:02 -0400

Plants respond most to red and blue light, at wavelengths of 430 and 662nm
(chlorophyll a) and 453 and 642nm (chlorophyll b).  The reason being, in
short, that the plant pigments absorb light at varying wavelengths
specific to the pigment,  some prfer blue light, some red, etc...  The
majority of light absorbed is in the visible spectrum of light, i.e., what
we humans see, and the green color of plant comes from the greater
absorption of red and blue light (remember that light is composed of 3
primary colors, red blue, and green).  Green light is reflected back the
most which is why we see plants as green.  However, DO NOT assume that
plants do not absorb other light colors, including green.  Other pigments
exist that absorb light at other color spots of the spectrum, such as
Caratenoids!  The reason for all of this has to do with antenae complexes
within the chloroplast that gather light for photosynthesis.  But, I'll
let you figure all that out yourself, it would take pages to really tell
you the long and short of it all!  Good luck, hope I helped!