Significance of Photosystem II Core Phosphorylation Heterogeneity for the Herbicide-Binding Domain

M aria Teresa Giardi Institute of Biochemistry and Ecophysiology of Plants, C N R Area della ricerca di Roma, Via Salaria km 29.3, 00016 M onterotondo Scalo, Italy Z. Naturforsch. 48c, 241 2 4 5 (1993); received November 9, 1992 Photosystem II Core, Phosphorylation, Heterogeneity, Phosphatase, Herbicide-Binding Domain In recent papers the heterogeneous nature of photosystem (PS) II core phosphorylation has been revealed (Giardi et al., BBRC 176, 1 2 9 8 -1 3 0 5 (1991); Plant Physiol. 100, 1 9 4 8 -1 9 5 4 (1992)). In this paper the action of endogenous and exogenous phosphatases both on the dis­ tribution of phosphorylated PS II core populations and on herbicide-binding activity in pho­ tosystem 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 D, and D2 proteins by endogenous phosphatase(s) and changes the relative distribution of phosphorylated photosys­ tem 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. De­ phosphorylation by the two alternative methods results in a differential modification of herbi­ cide-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.