The plant hormone abscisic acid (ABA) stimulates stomatal closure in response to various environmental stresses. Neill et al. show that synthesis and action of the signaling molecule nitric oxide (NO) are required for ABA-induced stomatal closure by treating guard cells of the pea with either NO scavengers or donors, or with NO synthase inhibitors, prior to exposure to ABA. An increase in NO synthesis in guard cells in response to ABA could be visualized and correlated with stomatal closure. The authors speculate that an observed increase in guanosine 3′,5′-monophosphate (cGMP) in response to NO production could regulate ion channels that effect stomatal closure.
S. J. Neill, R. Desikan, A. Clarke, J. T. Hancock, Nitric oxide is a novel component of abscisic acid signaling in stomatal guard cells, Plant Physiol. 128, 13-16 (2002).