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Biochemical and structural analyses of a higher plant photosystem II supercomplex of a photosystem I‐less mutant of barley
Author(s) -
Morosinotto Tomas,
Bassi Roberto,
Frigerio Sara,
Finazzi Giovanni,
Morris Edward,
Barber James
Publication year - 2006
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2006.05465.x
Subject(s) - photosystem ii , photosystem i , light harvesting complexes of green plants , photosystem , p700 , photosynthetic reaction centre , photoprotection , photosynthesis , hordeum vulgare , biology , chlorophyll , cytochrome b6f complex , thylakoid , biophysics , photochemistry , chemistry , biochemistry , chloroplast , botany , poaceae , gene
Photosystem II of higher plants is a multisubunit transmembrane complex composed of a core moiety and an extensive peripheral antenna system. The number of antenna polypeptides per core complex is modulated following environmental conditions in order to optimize photosynthetic performance. In this study, we used a barley ( Hordeum vulgare ) mutant, viridis zb63 , which lacks photosystem I, to mimic extreme and chronic overexcitation of photosystem II. The mutation was shown to reduce the photosystem II antenna to a minimal size of about 100 chlorophylls per photosystem II reaction centre, which was not further reducible. The minimal photosystem II unit was analysed by biochemical methods and by electron microscopy, and found to consist of a dimeric photosystem II reaction centre core surrounded by monomeric Lhcb4 (chlorophyll protein 29), Lhcb5 (chlorophyll protein 26) and trimeric light‐harvesting complex II antenna proteins. This minimal photosystem II unit forms arrays in vivo , possibly to increase the efficiency of energy distribution and provide photoprotection. In wild‐type plants, an additional antenna protein, chlorophyll protein 24 (Lhcb6), which is not expressed in viridis zb63 , is proposed to associate to this minimal unit and stabilize larger antenna systems when needed. The analysis of the mutant also revealed the presence of two distinct signalling pathways activated by excess light absorbed by photosystem II: one, dependent on the redox state of the electron transport chain, is involved in the regulation of antenna size, and the second, more directly linked to the level of photoinhibitory stress perceived by the cell, participates in regulating carotenoid biosynthesis.