Differential drought-induced modulation of ozone tolerance in winter wheat species

Recent reports challenge the widely accepted idea that drought may offer protection against ozone (O-3) damage in plants. However, little is known about the impact of drought on the magnitude of O-3 tolerance in winter wheat species. Two winter wheat species with contrasting sensitivity to O-3 (O-3 tolerant, primitive wheat, T. turgidum ssp. durum; O-3 sensitive, modern wheat, T. aestivum L. cv. Xiaoyan 22) were exposed to O-3 (83ppb O-3, 7h d(-1)) and/or drought (42% soil water capacity) from flowering to grain maturity to assess drought-induced modulation of O-3 tolerance. Plant responses to stress treatments were assessed by determining in vivo biochemical parameters, gas exchange, chlorophyll a fluorescence, and grain yield. The primitive wheat demonstrated higher O-3 tolerance than the modern species, with the latter exhibiting higher drought tolerance than the former. This suggested that there was no cross-tolerance of the two stresses when applied separately in these species/cultivars of winter wheat. The primitive wheat lost O-3 tolerance, while the modern species showed improved tolerance to O-3 under combined drought and O-3 exposure. This indicated the existence of differential behaviour of the two wheat species between a single stress and the combination of the two stresses. The observed O-3 tolerance in the two wheat species was related to their magnitude of drought tolerance under a combination of drought and O-3 exposure. The results clearly demonstrate that O-3 tolerance of a drought-sensitive winter wheat species can be completely lost under combined drought and O-3 exposure.