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Evidence that phosphorylation and dephosphorylation regulate the distribution of excitation energy between the two photosystems of photosynthesis in vivo: Photoacoustic and fluorimetric study of an intact leaf.
MedLine Citation:
PMID:  16593434     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Abstract/OtherAbstract:
State 1-state 2 transitions in an intact tobacco leaf were monitored by the photoacoustic method. Modulated oxygen evolution yield and its enhancement by continuous far-red light ("Emerson enhancement") were used to characterize the balance of light distribution between the two photosystems. These measurements were additionally supported by fluorimetry. Adaptation of the leaf to far-red light (lambda [unk] 700 nm), mainly absorbed in photosystem I (light 1), results in state 1, where short-wavelength light (light 2) is distributed in favor of photosystem II. This is shown by a low yield of oxygen evolution, a high extent of Emerson enhancement, a concomitantly high extent of fluorescence quenching by far-red light, and a low ratio of the 77 K emission peaks at 730 and 695 nm. The magnitudes of these parameters were reversed when the leaf was adapted to light 2 (state 2), indicating a change towards a more equal distribution of the excitation between the two photosystems. Preincubation of an intact leaf with NaF, a specific phosphatase inhibitor, stimulated the extent of adaptation to light 2, shown by all the above criteria, and completely abolished adaptation to light 1. Light 1 preillumination prior to NaF treatment resulted initially in state 1, but then a transition to state 2 was irreversibly induced by any light. The NaF effect was specific because NaCl did not affect the state 1-state 2 transitions. Leaching out the NaF restored the original physiological transitions of the leaf. NaF presumably acts here in the same way as it acts in isolated thylakoids-by blocking the dephosphorylation of membranal proteins (particularly the chlorophyll a/b-protein complex) phosphorylated by a light 2-activated kinase. Our results give direct support to the suggestion [Allen, J. F., Bennett, J., Steinback, K. E. & Arntzen, C. J. (1981) Nature (London) 291, 25-29] that it is the phosphorylation level of thylakoid proteins that controls the light distribution between the two photosystems in vivo, shown previously in isolated thylakoids.
Authors:
O Canaani; J Barber; S Malkin
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Proceedings of the National Academy of Sciences of the United States of America     Volume:  81     ISSN:  0027-8424     ISO Abbreviation:  Proc. Natl. Acad. Sci. U.S.A.     Publication Date:  1984 Mar 
Date Detail:
Created Date:  2010-06-30     Completed Date:  2010-06-30     Revised Date:  2010-09-15    
Medline Journal Info:
Nlm Unique ID:  7505876     Medline TA:  Proc Natl Acad Sci U S A     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1614-8     Citation Subset:  -    
Affiliation:
Biochemistry Department, Weizmann Institute of Science, Rehovot 76100, Israel.
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