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Plant Physiology 79:777-786 (1985)
© 1985 American Society of Plant Biologists

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Articles

Studies on the Photoactivation of the Water-Oxidizing Enzyme 1

I. Processes Limiting Photoactivation in Hydroxylamine-Extracted Leaf Segments

Franklin Ellis Callahan2 and George M. Cheniae

Department of Agronomy, University of Kentucky, Lexington, Kentucky 40546-0091

In weak yet optimal light intensity, complete photoactivation of the water-oxidizing enzyme in NH2OH-extracted wheat (Triticum aestivum, var Oasis) leaf segments could be obtained only after long dark preincubation. Photoactivation was not affected by ethylenediaminetetraacetate or inhibitors of photophosphorylation and protein synthesis, but was partially inhibited by a divalent cation ionophore. Complete photoactivation required ligation of ~4 Mn by the water oxidizing enzyme.

Without dark preincubation, photosystem II (PSII) was susceptible to weak light photoinhibition resulting in: (a) 50% maximum decrease in photooxidation of artificial electron donors by PSII: (b) increased times for the variable fluorescence rise (with 3-(3,4-dichlorophenyl)-1,1-dimethyl urea): (c) abolishment of photoactivation: and (d) the imposition of sensitivity to inhibitors of photophosphorylation and 70S but not 80S protein synthesis on subsequent light-dependent recovery from photoinhibition and recovery of O2 evolution. Decrease in susceptibility to photoinhibition and increase in rates of photoactivation resulting from dark preincubations proved closely correlated. Neither protein synthesis nor increases in abundances of thylakoid Mn2+ and Ca2+ were required for escape from photoinhibition. However, photoactivation of the wateroxidizing enzyme in NH2OH-extracted Chlamydomonas occurred in absence of dark preincubation and protein synthesis. Results are discussed in the context of disassembly/reassembly/resynthesis of specific PSII polypeptides.

2 Present address: Department of Biology, Florida State University, Tallahassee, FL 32306.

1 Supported in part by United States Department of Agriculture-Science and Education Administration (82-CRCR-1-1062), National Science Foundation (PCM-811827), and Department of Energy (DE-AS05-83ER13072). This paper (85-3-24) is published with the approval of the Director of the Kentucky Agricultural Experiment Station.






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Copyright © 1985 by the American Society of Plant Biologists