Abstract In recent papers the heterogeneous nature of photosystem (PS) II core phosphorylation has been revealed (Giardi et al., BBRC 176, 1298 -1305 (1991); Plant Physiol. 100, 1948 -1954 (1992)). In this paper the action of endogenous and exogenous phosphatases both on the distribution of phosphorylated PS II core populations and on herbicide-binding activity in photosystem II preparations from Spinacia oleracea L. has been investigated. The results indicate that these phosphatases modify the photosystem II core phosphorylation heterogeneity at a different level. Dark incubation causes a partial dephosphorylation of D1 and D2 proteins by endogenous phosphatase(s) and changes the relative distribution of phosphorylated photosystem II core populations, while the action of the alkaline phosphatase leads to extensive dephosphorylation and to the detachment of PsbH protein from the photosystem II core. Dephosphorylation by the two alternative methods results in a differential modification of herbicide-binding activity. It is suggested that photosystem II heterogeneity with respect to the herbicide action, observed in vivo, could be a consequence of PS II core phosphorylation heterogeneity.
