[Plant-education] balancing the photosystems

Jon Monroe via plant-ed%40net.bio.net (by monroejd from jmu.edu)
Wed Mar 4 10:03:46 EST 2009

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.


 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.edu

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