Abstract
Protein phosphorylation may be required for plant cell response to phytohormones and other extracellular signals. Protein phosphorylation and protein kinase activity in the culm of heading time of rice (Oryza sativa L.) were studied. Before heading, protein kinase activity was increased by Ca<2+> in the membrane fraction of the panicle and culm. The protein kinases with Mr of 51, 900, 49, 200, and 45, 500 isolated from the membrane fraction of culm increased the protein phosphorylation of Mr and pI of 40, 000/7.5 and 40, 000/7.6 in the culm extract. The activation of protein kinases, associated with membrane and subsequent protein phosphorylation, thus appears to be involved in the regulation of heading time in rice.
