[Induction and activity changes of protein kinase in grape leaves under heat stress]

The type and activity of protein kinase induced and activated by heat stress were studied in leaves of "Jingxiu" grape (Vitis vinifera L. cv. Jingxiu). The results showed that a 52-kD protein kinase was evidently activated by heat stress in 10 to 60 min. Myelin basic protein (MBP) embedded in gel could be phosphorylated by the 52 kD protein kinase. The phosphorylating activity of this kinase was determined by using MBP as the substrate and measuring the products of phosphorylation by autoradiography. The 52 kD protein kinase could not affect histone-III embedded as the substrate in gel and the products of phosphorylation by autoradiography was not displayed. High phosphorylation activity of this protein kinase was found with MBP substrate in solution reaction system. After 60 min heat stress, the activity of this protein kinase reached its maximum value, and then declined rapidly. Compared with control, the activity of protein kinase had no difference when histone-III was used as substrate in reaction system. The activity of this protein kinase was not enhanced by Ca(2+), showing that it was not Ca(2+)-dependent. The tyrosine-specific protein phosphatase (YOP) could significantly inactivate the phosphorylation activity of protein kinase. All results demonstrate that the 52 kD protein kinase activated by heat stress belong to the MAPK family.