ROS production and its detoxification in early and late sown cultivars of wheat under future O concentration.

The present field study was planned with an objective to unravel the mechanisms behind the differential responses of early and late sown wheat cultivars with respect to their defense capacity to scavenge ROS induced under elevated O (EO). Experiments were performed under ambient and elevated levels of O (ambient + 20 ppb) to plants inside open-top chambers (OTCs). Ozone concentrations, stomatal flux of O and meteorological parameters were measured throughout the experiment. Contents of superoxide radicals (O) and hydrogen peroxide (HO) and their localization, lipid peroxidation, antioxidative enzyme activities, ascorbic acid and total phenolic contents were measured at vegetative and reproductive developmental stages. EO exposure induced higher stomatal flux of O in early sown cultivars. Higher contents of O, HO and lipid peroxidation were noticed under EO in all the cultivars but the magnitude of increases was higher in late sown cultivars at the reproductive stage. Activities of glutathione reductase (GR) and ascorbate peroxidase (APX) were higher in late sown cultivars under EO. Ascorbic acid and total phenolic contents were significantly higher in early sown than late sown cultivars under EO treatment. The present study concludes that early sown cultivars are more efficient in their defense response due to higher induction of enzymatic and non-enzymatic antioxidants, while the induction of enzymatic antioxidants was more distinct in late sown cultivars. Non-enzymatic linked defense mechanism requires additional metabolic cost than enzymatic defense, making early sown cultivars more susceptible to EO. Differential response of early and late sown cultivars with respect to antioxidative defense against O stress suggests that yield responses are governed by the time of sowing and intrinsic defense responses of the cultivars. In future with rising trend of O, early sown cultivars are expected to be more vulnerable to oxidative stress compared to late sown cultivars.