136.
Photosystem II membranes (D-PSII) were isolated from dark-grown spruce seedlings. All major PSII proteins except the 17- and 23-kDa extrinsic proteins were present in D-PSII. O
2 evolution and Mn content in D-PSII were negligible, while PSII-donor activity showed a value comparable to that of NH
2OH-treated PSII membranes (NH
2OH-L-PSII) from light-grown seedlings. Light incubation of D-PSII with 1 m M MnCl
2, 50 m M CaCl
2 and 100 μ M DCIP at pH 5.3 resulted in activation of the latent water-oxidizing complex. Accomplishment of photoactivation of PSII membranes from dark-grown spruce seedlings clearly indicates that only ligation of Mn
2+ to the apo-water oxidizing complex is required for expression of O
2 evolution, and that protein synthesis is not involved in the photoactivation process. There was no essential difference between 'photoactivation' of naturally Mn-free PSII membranes and 'photoreactivation' of artificially Mn-depleted PSII membranes on kinetics, pH dependence, Mn
2+-concentration dependence. However, kinetics and pH dependence of photoactivation were appreciably different in spruce PSII membranes and in PSII membranes of angiosperms such as wheat and spinach.
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