Signal coordination prior to, during, and after stomatal closure in response to drought stress

Authors: HUBER, ANNIKA - Cornell University; MELCHER, PETER - Ithaca College; Pineros, Miguel; SETTER, TIMOTHY - Cornell University; BAUERLE, TARYN - Cornell University

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2019
Publication Date: 7/31/2019
Citation: Huber, A., Melcher, P., Pineros, M., Setter, T., Bauerle, T. 2019. Signal coordination prior to, during, and after stomatal closure in response to drought stress. New Phytologist. 224:675-688.

Interpretive Summary: Environmental factors such as low rainfall, extreme temperatures, and salinity, among others, contribute to drought that affects agricultural productivity and food security. However, there is a lack of understanding of the mechanisms that recognize, transmit and decode drought-related stress. Using a multidisciplinary approach, we have investigated the timeline of the appearance and development of long distance, drought-induced signals by simultaneously measuring chemical, electrical and hydraulic–type signals in sunflower plants undergoing various drought stress intensities. We conclude that hydraulic signals, mostly changes in the turgor (rigidity) of leaf cells rather than embolism of the vascular conduits, underlie the early, upstream signals imitating the onset of a wide range of physiological drought related responses. This study provides the basis to understand how crop plants respond and adapt in response to changes in the environment.

Technical Abstract: Signal coordination in response to changes in water availability remains unclear, as does the role of embolism events in signaling drought stress. Sunflowers were exposed to two drought treatments of varying intensity while simultaneously monitoring changes in stomatal conductance, acoustic emissions (AE), turgor pressure, surface-level electrical potential, organ-level water potential and leaf abscisic acid (ABA) con-centration. Leaf, stem and root xylem vulnerability to embolism were measured with the single vessel injection technique. In both drought treatments, it was found that AE events and turgor changes preceded the onset of stomatal closure, whereas electrical surface potentials shifted concurrently with stomatal closure. Leaf-level ABA concentration did not change until after stomata were closed. Roots and petioles were equally vulnerable to drought stress based on the single vessel injection technique. However, anatomical analysis of the xylem indicated that the increased AEevents were not a result of xylem embolism formation. Additionally, roots and stems never reached a xylem pressure threshold that would initiate runaway embolism throughout the entire experiment. It is concluded that stomatal closure was not embolism-driven, but, rather, that onset of stomatal closure was most closely correlated with the hydraulic signal from changes in leafturgor.