Coordinating the overall stomatal response of plants: Rapid leaf-to-leaf communication during light stress.

The plant canopy functions as an aerial array of light-harvesting antennas. To achieve maximal yield, each leaf within this array and the array as a whole need to rapidly adjust to naturally occurring fluctuations in light intensity and quality. Excessive light stress triggers the closing of pores in leaves called stomata to minimize moisture loss. We found that different leaves within the canopy of an plant, including leaves not directly exposed to light, coordinated stomatal closure in response to light stress by sending and receiving rapid systemic signals. This response required the plant hormones abscisic acid and jasmonic acid and was mediated by a rapid autopropagating wave of reactive oxygen species (ROS) production. Furthermore, this response depended on the function of genes encoding the ROS-generating NADPH oxidase RBOHD and various stomatal regulators, such as the anion channel SLAC1, GHR1 (guard cell hydrogen peroxide resistant 1), and lipoxygenase 1 (LOX1). Our findings reveal that plants function as highly dynamic and coordinated organisms, optimizing the overall response of their canopies to fluctuating light intensities.