PHOSPHORYLATION OF POLLEN PROTEINS IN RELATION TO SELF-INCOMPATIBILITY IN RYE (SECALE-CEREALE L)

The gametophytic two-locus self-incompatibility (SI) system in rye was investigated in view of a possible involvement of protein phosphoryla tion and Ca2+ as constituents of a signal transduction mechanism. Phos phorylation kinetics in pollen grains was found to be significantly di fferent after in vitro treatment of pollen with either ''cross'' or '' self' stigma proteins, with a pronounced phosphorylation activity in s elf-treated pollen grains. Loss of SI in self-compatible (SC) mutants was associated with a significantly decreased basic phosphorylation ac tivity in untreated pollen grains as compared to SI genotypes. Separat ion of phosphorylated pollen proteins by SDS-PAGE reveals four major p roteins in the MW range of 43-82 kDa which were differently phosphoryl ated in SI vs SC genotypes as well as in cross vs self-treated pollen grains. Application of different protein kinase inhibitors and the Ca2 + antagonists verapamil and La3+ to isolated stigmas resulted in an in hibition of the SI response in in vitro self-pollination. The role of protein kinases and Ca2+ as constituents of a putative SI-specific sig nal transduction mechanism is discussed.