Role of calcium and calmodulin in protein phosphorylation and auxin induced cell elongation

alcium is being recognized as a second messenger in plants. Calcium binding protein "Calmodulin" is known to regulate several biochemical and physiological processes of plants. In this study calmodulin antagonists such as chlorpromazine (CP), trifluoperazine and naphthalenesulfonamide derivatives (W-7) inhibited auxin-induced oat (Avena sativa) and corn (Zea mays L.) coleoptile elongation at micromolar concentrations. Amount of amino acids released in the presence of W-7 and W-5 was significantly lower than the amount in the presence of CP. The inhibitory effect of W-7 was reversible even after 12 h of treatment. These results suggested the involvement of calmodulin in auxin-induced elongation. In vitro phosphorylation was performed using soluble and membrane proteins isolated from tomato fruits. Micromolar concentrations of calcium enhanced phosphorylation and further enhancement was observed in the presence of exogenously supplied calmodulin. Calmodulin antagonists inhibited phosphorylation of several proteins. Both qualitative and quantitative changes in calcium dependent phosphorylation were seen at different developmental stages. There was a general decrease in protein phosphorylation towards ripening. Further, in vivo phosphorylation studies were carried out using dark grown corn root tips. Calcium increased uptake of phosphorus, whereas EGTA and calcium ionophore A-23187 decreased it. Phosphorus concentration in the media was adjusted to obtain similar uptake under all treatments. Phosphoproteins were analyzed on two dimensional gel electrophoresis. EGTA and A-23187 decreased the label in at least five polypeptides, whereas replenishment of calcium enhanced the phosphorylation of those five polypeptides. A short term (10 min) calcium treatment of roots preloaded with...