Ca²⁺ ‐dependent protein phosphorylation in germinated pollen of <i>Nicotiana alata</i>, an ornamental tobacco

Abstract

The 40 000 g supernatant and 40 000 g pellet from extracts of germinated pollen of Nicotiana alata Link et Otto contain protein kinase activity which catalyzes the phosphorylation of histones, casein and a range of endogenous polypeptides. Phosphorylation of certain low‐molecular‐weight, casein‐derived polypeptides is activated at low (12–37 μ M ) and partially inhibited at higher (540 μ M ) concentrations of free Ca 2+ . Histone phosphorylation is largely Ca 2+ ‐dependent and is activated by 540 μM free Ca 2+ . No activation of protein phosphorylation by micromolar concentrations of calmodulin is found, but phenothiazine‐derived calmodulin antagonists markedly stimulate protein phosphorylation.