withoutasoul
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can someone please explain to me this?
Many trees have leaves that are green in the summer and red, yellow, or orange in autumn. Where were these colors during the summer? How can they
suddenly appear in autumn?
thanx 
[Edited on 18-11-2003 by withoutasoul]
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Blind Angel
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I think they are due to the disparition of Chlorophyle or by it's oxidation while it's "die", but this is personnal though so it
may not be true...
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chemoleo
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there are many chlorophyll-type compounds, and plant hormones trigger their release/degradation.
These colours are a result of their respective absorbtive range.
Chlorophyll absorbs in the red and blue range within the visible spectrum (resulting in green as the colour you see), while phycoerythrin absorbs blue
and green ( resulting in red/orange), and phycocyanin absorbs yellow light. These pigments adsorb most of the visible light, and have the leftover of
the green colour (during summer.. thus explaining why it is very dark under a jungle tree foliage).
Hence, during the seasonal cycle, certain chlorophylls are degraded sequentially, resulting in different absorptive spectra. I think yellow leaves
correspond to remaining xantophyll (cant remember how it's spelled.).
PS Yes there are plant hormones (it's not just in animals). One prominent one is ethylene (CH2-CH2), which is used for ripening fruit (such as
bananas)
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JustMe
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Hm, you might try paying attention in class, the answer to this question is grade school level science.
Anyway, a simple google search brought up a number of sites with a more indepth answer, such as:
http://www.na.fs.fed.us/spfo/pubs/misc/leaves/leaves.htm
Short answer, the colors were always there, only masked by the chlorophyll.
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unionised
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Or you could look a little further than grade school like
http://www.botany.utoronto.ca/ResearchLabs/Feild_Lab/Feild_r...
and find that the colours are not all there before the Autumn. (The site you cited says that too, the red colours were not there all along).
[Edited on 20-11-2003 by unionised]
[Edited on 20-11-2003 by unionised]
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foreign maple
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i think the pigments are there the whole time. i preformed TLC on a maple leaf and it had many colors including green, red, yellow and brown so the
answer is that they are there the whole time but i think the chlorophyll gets degraded probably due to a hormone release during colder temperatures
leaving behind phycoerythrin and phycocyanin.
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TriiodideFrog
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The Short Answer:
As summer fades into fall, the days start getting shorter and there is less sunlight. This is a signal for the leaf to prepare for winter and to stop
making chlorophyll. Once this happens, the green colour fades, then yellow and orange pigments known as carotenoids are revealed in the leaves of many
species. In other plants, pigments called anthocyanins accumulate in the leaves at this time, giving them shades of red and purple.
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