title: Hexokinase mediates stomatal closure.
abstract: Stomata, composed of two guard cells, are the gates whose controlled movement allows the plant to balance the demand for CO2 for photosynthesis with the loss of water through transpiration. Increased guard-cell osmolarity leads to the opening of the stomata and decreased osmolarity causes the stomata to close. The role of sugars in the regulation of stomata is not yet clear. In this study, we examined the role of hexokinase (HXK), a sugar-phosphorylating enzyme involved in sugar-sensing, in guard cells and its effect on stomatal aperture. We show here that increased expression of HXK in guard cells accelerates stomatal closure. We further show that this closure is induced by sugar and is mediated by abscisic acid. These findings support the existence of a feedback-inhibition mechanism that is mediated by a product of photosynthesis, namely sucrose. When the rate of sucrose production exceeds the rate at which sucrose is loaded into the phloem, the surplus sucrose is carried toward the stomata by the transpiration stream and stimulates stomatal closure via HXK, thereby preventing the loss of precious water.
authors.affiliation: Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel.
authors.forename: Gilor
authors.initials: G
authors.lastname: Kelly
authors.forename: Menachem
authors.initials: M
authors.lastname: Moshelion
authors.forename: Rakefet
authors.initials: R
authors.lastname: David-Schwartz
authors.forename: Ofer
authors.initials: O
authors.lastname: Halperin
authors.forename: Rony
authors.initials: R
authors.lastname: Wallach
authors.forename: Ziv
authors.initials: Z
authors.lastname: Attia
authors.forename: Eduard
authors.initials: E
authors.lastname: Belausov
authors.forename: David
authors.initials: D
authors.lastname: Granot
mesh_terms: D000040:Abscisic Acid / Q000502:physiology; D029681:Arabidopsis Proteins / Q000502:physiology*; D006593:Hexokinase / Q000502:physiology*; D018551:Solanum lycopersicum; D009569:Nitric Oxide / Q000378:metabolism; D054046:Plant Stomata / Q000201:enzymology*; D018526:Plant Transpiration; D030821:Plants, Genetically Modified; D013395:Sucrose / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D009569:Nitric Oxide; D013395:Sucrose; D000040:Abscisic Acid; D006593:Hexokinase; C473630:ATHXK1 protein, Arabidopsis
keywords: abscisic acid; guard cells; hexokinase; stomata; sucrose; transpiration