Photoactivation of Oxygen-Evolving Enzyme in Dark-Grown Pine Cotyledons: Relationship between Assembly of Photosystem II Proteins and Integration of Manganese and Calcium

Dark-grown cotyledons of pine (Pinus thunbergit) did not exhibitO₂ evolution, but this capability was rapidly activated by illuminationfor a short period (photoactivation). To examine the biochemicalchanges which accompany the process of photoactivation in gymnosperms,a method enabling the preparation of highly active O₂-evolvingphotosystem II (PS II) membranes was applied to light-grown,dark-grown, and photoactivated cotyledons. PS II membranes preparedfrom light-grown cotyledons exhibited high O₂-evolving activity,and contained all the intrinsic proteins as well as the threeextrinsic proteins (32, 23 and 17 kDa) associated with PS II.These membranes were also found to contain 4.4 Mn and 0.83 Ca/PSII reaction center. PS II membranes from dark-grown cotyledonscontained all the intrinsic proteins, but preserved only 32kDa extrinsic protein, and zero Mn and 0.85 Ca/PS II reactioncenter. The two extrinsic proteins (23 and 17 kDa) absent inthe PS II membranes from dark-grown cotyledons were, however,present as mature forms in whole thylakoid membranes from thecorresponding sample. The PS II membranes isolated from photoactivatedcotyledons showed a high activity of O₂ evolution and retainedthe three extrinsic proteins, 5.3 Mn and 1.1 Ca/PS II reactioncenter, respectively. The results indicated that Mn and thetwo extrinsic proteins were tightly integrated in the O₂-evolvingapparatusduring the process of photoactivation but integration of Capreceded the integration of Mn by photoactivation. (Received December 9, 1991; Accepted February 1, 1992)