Hi Plant-eders,
I really like describing the mechanism for balancing light input into
the two photosystems of chloroplasts (redox state of PQ, activation
state of a protein kinase, phosphorylation state of LHC, location of LHC
in stacked or unstacked regions...) but I can't understand part of it
and hence my students are frustrated. The reason the two photosystems
can be unbalanced is because they operate at different wavelengths (680,
700 nm), and all would make sense if those were the /only/ wavelengths
received by the photosystems, but they aren't. Arrays of chl a, b and
beta-carotene surround each photosystem allowing photos of many
wavelengths to donate their energy to the reaction centers. I recall
learning that from mid-day to dusk the quality of light changes and that
this was the difference, but is this really enough? Could it be that a
leaf shifting between full sun and canopy shade, in which the ratio of
red to far red light changes, is part of this story? Help! Thanks.
Jon
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Jonathan Monroe, Professor
Department of Biology, MSC 7801
James Madison University
Harrisonburg, VA 22801
office: 304 Burruss Hall
phone: 540-568-6649
fax: 540-568-3333
e-mail: monroejd from jmu.eduhttp://www.jmu.edu/biology/
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