Abstract
Blue light induces stomatal opening through the activation of the plasma membrane H+-ATPase. Recent investigations have demonstrated that blue light activates the H+-ATPase via phosphorylation on a penultimate threonine residue in the C-terminus and subsequent binding of 14-3-3 protein to the phosphorylated C-terminus in guard cells. However, protein kinase and protein phosphatase, which regulate the phosphorylation level of the H+-ATPase, are largely unknown. In this study, we analyzed biochemical properties of the H+-ATPase phosphorylation. in vitro phosphorylation on threonine residue in the C-terminus of the H+-ATPase was detected in the microsome from Vicia guard cell protoplasts and also detected in the plasma membrane from etiolated seedlings of Arabidopsis. Moreover, we found that a nonionic surfactant TritonX-100 has an inhibitory effect on in vitro phosphorylation. These results suggested that the protein kinase localized in the plasma membrane is common to plant cells and that structure of the plasma membrane may be requisite for the protein kinase activity.
