Abstract
The green alga Dunaliella salina responds to growth under high-intensity light by reducing the complement of auxiliary light-harvesting complexes integrated into the thylakoid membrane, giving a reduction in the functional chlorophyll antenna size for both photosystems. Acclimation of the antenna system of Photosystem II upon removal of high-light-adapted cells to a low-light regime was found to occur as a distinct sequence of reassembly events. Analysis of fluorescence-induction kinetics indicated a conversion step after 4 h of low-light acclimation in which PS II γ centres were converted to PS II β centres. Conversion of PS II β centres to PS II α centres proceeded after 12 h and was accompanied by an increase in PS II-variable fluorescence yield and PS II-quantum yield. Changes in chlorophyll a binding by the CP47 polypeptide of the PS II core preceded changes in membrane protein composition and reassembly of auxiliary antenna complexes, suggesting that regulation of assembly of the PS II antenna occurs at the level of chlorophyll synthesis. Chlorophyll binding by CP47 is not essential for its primary function in assembly of the complete photosynthetic unit. A model for the PS II antenna in which CP47 and CP43 act independently for excitation energy transfer to the PS II reaction centre is proposed and its implications are discussed.
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