Speeding up stomatal responses: A plant's cellular metabolism rapidly adjusts to changes in light conditions, but its stomata—pores that allow gas exchange in leaves—are slower to respond. Because of the lagging response, photosynthesis is less efficient, and excess water is lost through the open pores. Papanatsiou et al. introduced a blue light–responsive ion channel into stomata of the small mustard plant Arabidopsis. The channel increased the rate of stomata opening and closing in response to light. The engineered plants produced more biomass, especially in the fluctuating light conditions typical of outdoor growth. Science , this issue p. 1456

New evidence for ABA-induced stomatal closure in fern and known evidence in earlier diverging lineages does not support the hypothesis that stomatal responsiven

The discovery of the START family of abscisic acid (ABA) receptors places these proteins at the front of a protein kinase/phosphatase signal cascade that promotes stomatal closure. The connection of these receptors to Ca²⁺ signals evoked by ABA has proven more difficult to resolve, although it has been implicated by studies of the pyrbactin-insensitive pyr1/pyl1/pyl2/pyl4 quadruple mutant. One difficulty is that flux through plasma membrane Ca²⁺ channels and Ca²⁺ release from endomembrane stores coordinately elevate cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) in guard cells, and both processes are facilitated by ABA. Here, we describe a method for recording Ca²⁺ channels at the plasma membrane of intact guard cells of Arabidopsis (Arabidopsis thaliana). We have used this method to resolve the loss of ABA-evoked Ca²⁺ channel activity at the plasma membrane in the pyr1/pyl1/pyl2/pyl4 mutant and show the consequent suppression of [Ca²⁺]_i increases in vivo. The basal activity of Ca²⁺ channels was not affected in the mutant; raising the concentration of Ca²⁺ outside was sufficient to promote Ca²⁺ entry, to inactivate current carried by inward-rectifying K⁺ channels and to activate current carried by the anion channels, both of which are sensitive to [Ca²⁺]_i elevations. However, the ABA-dependent increase in reactive oxygen species (ROS) was impaired. Adding the ROS hydrogen peroxide was sufficient to activate the Ca²⁺ channels and trigger stomatal closure in the mutant. These results offer direct evidence of PYR/PYL/RCAR receptor coupling to the activation by ABA of plasma membrane Ca²⁺ channels through ROS, thus affecting [Ca²⁺]_i and its regulation of stomatal closure.

Fast stomatal opening kinetics in response to light in Arabidopsis depends on a tight coordination between membrane ion transport and metabolic rearrangements.