|MadSci Network: Biochemistry|
Actually, the color change in autumn leaves is not associated with the production of new colored pigments, such as anthocyanins, but with the breakdown of an existing one, chlorophyll. In the chloroplasts of higher plants, chlorophyll is bound up in a couple of very large and complex structures called Photosystem I and Photosystem II. These are similar in structure and both contain numerous chlorophyll molecules, pheophytin molecules (chlorophyll that is missing its central magnesium ion), other secondary pigments, and many proteins. As the plant prepares for winter, the Photosystems are disassembled so that the plant can keep the nutrients contained in them after the leaves drop off. The majority of the most valuable nutrients are in the proteins of the photosystems, but the plant must be careful to break down chlorophyll as well because it can be dangerous to the cell if not coupled with the rest of the photosynthetic apparatus. Chlorophyll that becomes excited by light in the absence of the photosynthetic apparatus can lead to the creation of highly reactive oxygen species (radicals, peroxides, etc.) that can damage other valuable parts of the plant cells. As the green of chlorophyll is lost, the color of other pigments such as carotenoids becomes visible.
There is still a lot of research to be done on chlorophyll breakdown. I was unable to find any really informative web links on it, but there are a couple of papers that have been published on the subject. One is by Philippe Matile, and Stefan Hortersteiner titled Chlorophyll Degradation, in Annu. Rev. Plant Physiol. Mol. Biol.1999, 50:67-95. You'll have to get that at a college library, or a librarian might be able to order a copy for you.
A site that probably has everything you'll ever want to know about anthocyanins is: http://scifun.chem.wisc.edu/chemweek/fallcolr/fallcolr.html
.. or try the MadSci Anthocyanins FAQs
And if you want to know more about photosynthesis, check out: http://www.life.uiuc.edu/bio100/Link_page/photosyn.htm
I hope that answers your question satisfactorily. If you need more information, a good multi-engine search engine is http://www.dogpile.com
And a good place to find references to science journal articles is: http://www.highwire.stanford.edu
J. Todd Holland
Graduate Student in Biophysics
University of Illinois at Urbana-Champaign
Try the links in the MadSci Library for more information on Biochemistry.