Blue light-induced H⁺-pumping in guard-cell protoplasts from Arabidopsis thaliana

Abstract

Blue light (BL) activates the plasma membrane H⁺-ATPase via phosphorylation, and induces stomatal opening. Recently, we showed that phototropins (phots) act as BL-receptors in stomatal opening using phot1phot2 double mutant of Arabidopsis thaliana. However, BL-responses using guard-cell protoplasts from Arabidopsis (AtGCPs) has not been investigated. In this study, we isolated AtGCPs and investigated H⁺-pumping in response to BL. The H⁺-ATPase, phot1 and phot2 were identified in AtGCPs using specific antibodies. H⁺-pumping in AtGCPs reached maximum 2 min after the start of BL (100 μmol/m²/sec for 30 sec), and sustained for 10 min. An inhibitor of protein kinase, staurosporin, at 5μ M inhibited H⁺-pumping. These results confirmed the identical properties of H⁺-pumping shown in GCPs from Vicia faba. Furthermore, we investigated BL-responses in phot1phot2. BL did not induce H⁺-pumping, although the H⁺-ATPase was observed in GCPs. These results indicated that phot1 and phot2 act as BL-receptors in stomatal opening.