The influence of ABA and IAA on in vivo phosphorylation of proteins in Funaria hygrometrica Hedw

In vivo phosphorylation patterns of Funaria protonemata (wild type and auxin-deficient mutants) were analyzed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE). In one of the mutants one soluble protein with enhanced phosphorylation could be indentified without hormone treatment in short-time experiments (45 min incubation with radioactive phosphate). Addition of 10 −6 M indole-3-acetic acid (IAA) did not lead to a change in protein phosphorylation neither in the wild type nor in the two mutants when incubated for 15 min or 14 h. Abscisic acid (ABA) treatment (10 −5 M) of the protonema caused various changes in protein phosphorylation detected after 14h of treatment in comparison to control protonemata, i.e. in soluble and mmicrosomal proteins. These changes could be suppressed by the addition of 10 −5 M cycloheximide to the growth medium, indicating that for this phosphorylation de novo protein synthesis is necessary. Only one microsomal protein is independent of the cycloheximide treatment. Because drought stress and ABA induce the formation of new proteins, shown by the isolation of extremely heat resistant soluble proteins, it is possible that such proteins are targets for phosphorylation. However, in slowly dried protonemata changes in protein phosphorylation differ from those induced by ABA. Therefore, ABA does not alone induce the changes which are the response to drought stress in this plant system.