Ca²⁺ dPKs from the protonema of the moss Funaria hygrometrica: effect of indole-acetic acid and cultural parameters on the activity of a 44 kDa Ca²⁺ dPK

Abstract

Using the in-gel kinase assay, four polypeptides of Mr 44, 48, 63, and 70 kDa showed calcium-dependent phosphorylation in the crude extract of the moss Funaria hygrometrica Hedw. Analysis by SDS-PAGE suggests that these phosphopolypeptides represent the calcium-dependent protein kinases (PK), which could undergo autophosphorylation and phosphorylate casein. Temporal changes in the activity of PK in cells grown under different conditions were detectable using the in-gel kinase assay. The 44 kDa Ca²⁺ dPK showed an increase in activity in cells grown either in the presence of auxin, at pH 5, or when starved of nitrate. This PK is shown to share epitopes with calmodulin suggesting that it could be a PK with calmodulin-like domain. The in-gel kinase assay, its possible applications and the existence of multiple Ca²⁺ dPKs in moss are discussed.