Mon Oct 12 10:14:06 EST 1998

Dear Botanical Pundits,

	With the return of fall colors, conversation here has turned to
matters of plant pigments.
	As I understand it, the reds and oranges in tree leaves during
autumnal senescence are due to carotenoids (unmasked by the loss of
chlorophyll) and anthocyanins.  The anthocyanins are overproduced because
daylight drives photosynthesis but the cool nights restrict translocation.
Thus, photosynthetically-fixed carbon is "disposed of" by dumping it in the
vacuole as anthocyanin.  Any corrections here?  Does the carotenoid content
of fall leaves increase as well?
	OK, if we believe all of that, then are the anthocyanins truly
waste products?  Are they ever remetabolized prior to leaf abscission?
What about the anthocyanin in beets (betalin?)?  Since beets are a storage
organ, would a plant "store" a waste product?  Of course, modern beets are
the result of centuries of selection by humans for agronomic traits.  Do
beet ancestors have red roots?  And on to carrots.  Are the orange roots of
carrots widespread in natural populations or is this a trait that has been
heavily selected for?


Dr. Robert R. Wise
Department of Biology and Microbiology
University of Wisconsin-Oshkosh
Oshkosh, WI  54901

(920) 424-3404 tel
(920) 424-1101 fax
wise at

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