K252a-sensitive protein kinases but not okadaic acid-sensitive protein phosphatases regulate methyl jasmonate-induced cytosolic Ca2+ oscillation in guard cells of Arabidopsis thaliana

Methyl jasmonate (MeJA) induces stomatal closure similar to abscisic acid (ABA), and MeJA signaling in guard cells shares some signal components with ABA signaling. As part of this process, MeJA as well as ABA induce the elevation and oscillation of cytosolic free-calcium concentrations ([Ca2+]cyt) in guard cells. While abscisic acid-induced [Ca2+]cyt oscillation has been extensively studied, MeJA-induced [Ca2+]cyt oscillation is less well understood. In this study, we investigated the effects of K252a (a broad-range protein kinase inhibitor) and okadaic acid (OA, a protein phosphatase 1 and 2A inhibitor) on MeJA-induced [Ca2+]cyt oscillation in guard cells of Arabidopsis thaliana ecotype Columbia expressing the Ca2+ reporter yellow cameleon 3.6. The protein kinase inhibitor K252a abolished MeJA-induced stomatal closure and reduced MeJA-elicited [Ca2+]cyt oscillation. The protein phosphatase inhibitor OA, on the other hand, did not inhibit these processes. These results suggest that MeJA signaling involves activation of K252a-sensitive protein kinases upstream of [Ca2+]cyt oscillation but not activation of an OA-sensitive protein phosphatase in guard cells of A. thaliana ecotype Columbia.