Ascorbic acid and thiols as potential biomarkers of ozone tolerance in tropical wheat cultivars.

Tropospheric ozone (O3) has been identified as the most damaging air pollutant to crop plants in terms of growth and yield reductions. Considering the negative effect of O3 in tropical regions, fourteen commonly grown Indian wheat cultivars with known sensitivity to O3 were tested for their sensitivity/tolerance with respect to two major antioxidants (ascorbic acid and thiols) and grain yield responses against elevated O3 (ambient + 30 ppb) exposure. The objectives of the study were to assess the usefulness of the biochemical markers in the screening of wheat cultivars having differential level of sensitivity to O3 and different release time (modern and old cultivars). Ozone exposure led to an upsurge of ascorbic acid, thiols as well as their ratio greatly in the tolerant group followed by the intermediately sensitive group while least in sensitive one. Both ascorbic acid and thiol contents offered more resistance to early released cultivars compared to modern ones. Ascorbic acid served to be the most influential parameter for determining varietal response under elevated O3 stress and directly linked with O3 tolerance. Overall, the sensitive group suffered maximum yield losses while the minimum was observed in the tolerant group due to the differential enhancement of tolerance offered by antioxidants. Higher concentrations of antioxidants at early growth stages were highly correlated with final yield responses suggesting the role of antioxidants as a determinant of final yield. Findings of this study will help in the identification of O3 tolerant and sensitive wheat cultivars for future screening programs using ascorbic acid and thiols as important markers of O3 tolerance.