Abstract
Growth suppression and
defense signaling are simultaneous strategies that plants invoke to
respond to abiotic stress. Here, we show that the drought stress
response of poplar trees (Populus trichocarpa ) is initiated by a
suppression in cell wall derived methanol (MeOH) emissions and
activation of acetic acid (AA) fermentation defenses. Temperature
sensitive emissions dominated by MeOH (AA/MeOH < 30%) were
observed from physiologically active leaves, branches, detached stems,
leaf cell wall isolations, and whole ecosystems. In contrast, drought
treatment resulted in a suppression of MeOH emissions and strong
enhancement in AA emissions together with fermentation volatiles
acetaldehyde, ethanol, and acetone. These drought-induced changes
coincided with a reduction in stomatal conductance, photosynthesis,
transpiration, and leaf water potential. The strong enhancement in
AA/MeOH emission ratios during drought (400-3,500%) was associated with
an increase in acetate content of whole leaf cell walls, which became
significantly 13C2-labeled following
the delivery of 13C2-acetate via the
transpiration stream. The results are consistent with MeOH and AA
production at high temperature in hydrated tissues associated with
accelerated primary cell wall growth processes, which are downregulated
during drought. Our observations are consistent with drought-induced
activation of aerobic fermentation driving high rates of foliar AA
emissions and enhancements in leaf cell wall O -acetylation. We
suggest that atmospheric AA/MeOH emission ratios could be useful as a
highly sensitive signal in studies investigating environmental and
biological factors influencing growth-defense trade-offs in plants and
ecosystems.