SIGNIFICANCE OF PHOTOSYSTEM-II CORE PHOSPHORYLATION HETEROGENEITY FORTHE HERBICIDE-BINDING DOMAIN

In recent papers the heterogeneous nature of photosystem (PS) 11 core phosphorylation has been revealed (Giardi et al., BBRC 176, 1298-1305 (1991); Plant Physiol. 100, 1948-1954 (1992)). In this paper the actio n of endogenous and exogenous phosphatases both on the distribution of phosphorylated PS II core populations and on herbicide-binding activi ty in photosystem II preparations from Spinacia oleracea L. has been i nvestigated. The results indicate that these phosphatases modify the p hotosystem II core phosphorylation heterogeneity at a different level. Dark incubation causes a partial dephosphorylation of D1 and D2 prote ins by endogenous phosphatase(s) and changes the relative distribution of phosphorylated photosystem II core populations, while the action o f the alkaline phosphatase lead's to extensive dephosphorylation and t o the detachment of PsbH protein from the photosystem II core. Dephosp horylation by the two alternative methods results in a differential mo dification of herbicide-binding activity. It is suggested that photosy stem II heterogeneity with respect to the herbicide action, observed i n vivo, could be a consequence of PS II core phosphorylation heterogen eity.