Complex interactive effects of drought and ozone stress on the antioxidant defence systems of two wheat cultivars

The response of antioxidative defence systems in flag leaf tissues of wheat to combinations of ozone and drought stress was investigated. Sensitive (Triticum aestivum Desf. cv. Nandu) and resistant (Triticum durum L. cv. Extradur) cultivars of wheat were grown in open-top chambers under two ozone (ambient; ambient plus 50 ppb) and two water regimes (well-watered and 40% of soil water capacity). Concentrations of antioxidants ascorbate, glutathione, and tocopherol as well as the contents of chloroplast pigments were determined to evaluate the capacity of radical scavenging systems. Additionally leaf water potential, stomatal conductance and chlorophyll fluorescence were measured. Leaf water potentials of the resistant cultivar were significantly lower than that of the sensitive cultivar grown under the same imposed drought exposure. Drought decreased total ascorbate and total chlorophyll concentrations, increased the protective carotenoids and the de-epoxidation state of the xanthophyll cycle as well as total glutathione and tocopherol concentrations. Drought stress combined with ozone exposure did not further affect the antioxidative system.