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RESEARCH PRODUCT

Cytochrome F as Indicator for the Interaction of the Two Photosystems in the State 1 and State 2

subject

description

The transition of plants into a State 1 or a State 2 by an excess of PS I or PS II excitation was described by BONAVENTURA and MYERS [1]. Since the time of their investigations fluorometric methods gained increasing importance in analyzing the distribution of energy between the two photosystems [21. It was possible to correlate the altered energy balance to the phosphorylation of LHCII and it’s migration into non-appressed thylakoid membranes [31. However fluorescence measurements can give only indirect evidences that also changes in the activity of the two photosystems are produced by the changed energy distribution. A direct assessment of the photochemical variations during state transitions was demonstrated by measuring partial reactions of PS I and PS II [4] or by tracing the behaviour of redox components located between both photosystems [5,6]. There are only a few studies with intact cells e.g. those of SATOH and FORK [7] who describe a ‘State 2 — State 3 transition’ with the red alga Porphyra perforata. Recently REHM et al. [8] have studied state transitions with intact cells of red algae by means of cytochrome f kinetics. They described a drastic decline of the apparent quantum yield of PS I under State 1 conditions. This study confirms their finding also for higher plants. It uses the absorption changes of cytochrome f but considers the influences of activation/inactivation processes which are possible in an intact leaf.