TOUCH-INDUCED PROTEIN-PHOSPHORYLATION IN MECHANOSENSITIVE TENDRILS OFBRYONIA-DIOICA JACQ

Protein phosphorylation was analyzed in Bryonia dioica tendrils using in vitro assays. The major microsomal phosphoproteins had apparent mol ecular masses of 120 (p120), 58 (p58), 45 (p45) and 36 (p36) kDa and c ontained phosphoserine; p36 was additionally phosphorylated at threoni ne residues, and p120 was found to be tendril-specific. Phosphorylatio n of p120, p45, p36 and, to a lesser extent, of p58 was stimulated by calcium in the range of physiological concentrations. Mechanical stimu lation of tendrils resulted in a rapid increase in incorporation of ra dioactive phosphate from [gamma-P-32]-ATP into all microsomal phosphop roteins studied in the in vitro assay. Among the predominant phosphopr oteins studied here, only p58 was found to autophosphorylate. Further analysis showed that plasma membrane and endomembrane p58 differed in several properties, including pi values. It is thus likely that p58 re presents different isoforms of a dominant, membrane associated protein kinase with CDPK-like properties. Staurosporine strongly inhibited th e phosphorylation of all proteins as well as mechanically induced tend ril coiling. Collectively, the data show that protein phosphorylation is an important component in mechanical signaling in B. dioica tendril s.