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Sending a canopy-wide message
A stress experienced by one part of a plant can be transmitted to other parts of the plant not directly exposed to the stress. Although not all leaves in the canopy of a plant may be exposed to light at the same time, it is beneficial to coordinate the closure of pores in leaves called stomata to prevent desiccation. Devireddy et al. showed that a wave of reactive oxygen species (ROS) and Ca2+ enabled leaves experiencing light stress in Arabidopsis thaliana plants to trigger stomatal closure in leaves not exposed to light. Stomatal closure required abscisic acid in light-stressed leaves and jasmonic acid in nonexposed leaves, hormones previously implicated in stomatal closure. This coordinated and dynamic response may enable plants to acclimate to light stress.
Abstract
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 Arabidopsis thaliana 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.
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