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Old 15-06-2003, 03:20 PM
Jrg Sczepek
 
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Default Do leaves change their colour according to the brightness ?

Im trying to understand why we perceive colours in nature different
in dependency on the intensity of the illumination. According to this
I read that the chlorophyll cells in leaves can change their position
away from the center to the periphery if the illumination is very
bright. Can anybody tell me if this really the case as, say a kind of
protection mechanism against "overexposure", and if it can lead to a
different colour impression ?
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Old 18-06-2003, 02:08 AM
David Hershey
 
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Default Do leaves change their colour according to the brightness ?

You are correct that plant chloroplasts are able to move in the leaf
cells depending on the light level. This movement in response to light
is termed phototaxis. It can maximize light interception under low
light conditions and minimize damage to chlorophyll under high light
conditions.

To determine experimentally if chloroplast phototaxis affects leaf
color as perceived by the human eye would require that you have a
mutant plant with chloroplasts that lack phototaxis. You could then
compare the mutant plant with a normal plant. The following article
describes a mutant tobacco plant that has leaf cells with two to three
large choroplasts per cell. These large chloroplasts lack phototaxis.
A normal tobacco plant has cells with numerous smaller chloroplasts
that do exhibit phototaxis. Thus, you should be able to test your
hypothesis.

http://library.kribb.re.kr/research/pdf-2002/3976.pdf

You would also need to test an inanimate green object to determine if
the human eye sees different shades of green depending on the light
level. It might be that the light level will have a larger effect on
color perception than chloroplast phototaxis.


David R. Hershey



(Jrg Sczepek) wrote in message om...
Im trying to understand why we perceive colours in nature different
in dependency on the intensity of the illumination. According to this
I read that the chlorophyll cells in leaves can change their position
away from the center to the periphery if the illumination is very
bright. Can anybody tell me if this really the case as, say a kind of
protection mechanism against "overexposure", and if it can lead to a
different colour impression ?

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Old 20-06-2003, 05:20 PM
Beverly Erlebacher
 
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Default Do leaves change their colour according to the brightness ?

In article ,
Mike Lyle wrote:
(David Hershey) wrote in message . com...
You are correct that plant chloroplasts are able to move in the leaf
cells depending on the light level.[...etc...]


OK, you've answered the intelligent question. Now, how about a naive
one? I've sometimes wondered if the reactions involved in green
vegetation's sensitivity to light could have been exploited to form
the basis of a photographic process not dependent on silver compounds.


Well, you can put a stencil on an apple and when it ripens, the part that
was covered will not have turned red. This has been recommended to delight
little kids by putting their names on apples. I think you can do this
with dark green winter squashes too - the covered part is orange. Maybe
I should try it this year - I could get on the front page of the National
Inquirer (Face of Jesus Appears on Woman's Squash! Cucurbit Apocalypse
Predicted!)

It's more like old fashioned blueprints than photography, though.

OK, I said it was naive. But if it goes on to get you a Nobel Prize,
try to remember me in the speech of thanks!


I like the idea: dynamic videos on rhubarb leaves, perhaps. A new goal
for genetic engineering!

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Old 23-06-2003, 09:12 PM
Mike Lyle
 
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Default Do leaves change their colour according to the brightness ?

(Beverly Erlebacher) wrote in message ...
In article ,
Mike Lyle wrote:
(David Hershey) wrote in message . com...
You are correct that plant chloroplasts are able to move in the leaf
cells depending on the light level.[...etc...]


OK, you've answered the intelligent question. Now, how about a naive
one? I've sometimes wondered if the reactions involved in green
vegetation's sensitivity to light could have been exploited to form
the basis of a photographic process not dependent on silver compounds.


Well, you can put a stencil on an apple and when it ripens, the part that
was covered will not have turned red. This has been recommended to delight
little kids by putting their names on apples. I think you can do this
with dark green winter squashes too - the covered part is orange. Maybe
I should try it this year - I could get on the front page of the National
Inquirer (Face of Jesus Appears on Woman's Squash! Cucurbit Apocalypse
Predicted!)

It's more like old fashioned blueprints than photography, though.

OK, I said it was naive. But if it goes on to get you a Nobel Prize,
try to remember me in the speech of thanks!


I like the idea: dynamic videos on rhubarb leaves, perhaps. A new goal
for genetic engineering!


We should get together! (I've actually done the apple thing: it
works.) But I hope David realizes I was asking about the reactions
themselves, separate from the leaves.

Mike.


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Old 25-06-2003, 04:32 AM
David Hershey
 
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Default Do leaves change their colour according to the brightness ?

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You can crudely use leaves to make starch prints.

A botany lab exercise uses a black and white photographic negative and
an attached leaf to make a starch print. The leaf should have been in
the dark for 24 hours so it contains no starch. The negative is
fastened to the upper leaf surface and the leaf exposed to light from
that side for several hours. The leaf is then detached, cleared of
chlorophyll by boiling in alcohol and the print developed by applying
an iodine solution to the leaf. The iodine turns the starch black.

Experiments in Plant Physiology by Carol Reiss gives detailed
instructions.

This site also gives instructions:
http://www.northern.edu/ramsayj/Bota...bonfixlab.html

David Hershey





(Mike Lyle) wrote in message . com...
(Beverly Erlebacher) wrote in message ...
In article ,
Mike Lyle wrote:
(David Hershey) wrote in message . com...
You are correct that plant chloroplasts are able to move in the leaf
cells depending on the light level.[...etc...]

OK, you've answered the intelligent question. Now, how about a naive
one? I've sometimes wondered if the reactions involved in green
vegetation's sensitivity to light could have been exploited to form
the basis of a photographic process not dependent on silver compounds.


Well, you can put a stencil on an apple and when it ripens, the part that
was covered will not have turned red. This has been recommended to delight
little kids by putting their names on apples. I think you can do this
with dark green winter squashes too - the covered part is orange. Maybe
I should try it this year - I could get on the front page of the National
Inquirer (Face of Jesus Appears on Woman's Squash! Cucurbit Apocalypse
Predicted!)

It's more like old fashioned blueprints than photography, though.

OK, I said it was naive. But if it goes on to get you a Nobel Prize,
try to remember me in the speech of thanks!


I like the idea: dynamic videos on rhubarb leaves, perhaps. A new goal
for genetic engineering!


We should get together! (I've actually done the apple thing: it
works.) But I hope David realizes I was asking about the reactions
themselves, separate from the leaves.

Mike.

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