Variability in defence mechanism operating in three wheat cultivars having different levels of sensitivity against elevated ozone

Wheat cultivars namely HD 2987 [ozone (O3) sensitive], PBW 502 (intermediately sensitive to O3) and Kharchiya 65 (O3 tolerant) were chosen on the basis of earlier study to investigate the effect of elevated O3 (ambient + 30 ppb) on histochemical localisation assay, native-PAGE analysis, metabolites and enzymes of antioxidative and phenylpropanoid pathway as well as on reproductive structures and related yield losses. In the histochemical study, highly distinguished and intensified stains were found in leaf tissues of sensitive cultivar due to the formation of reactive oxygen species (ROS). Greatest induction in activities of enzymes i.e. superoxide dismutase (SOD), peroxidase (POX), glutathione reductase (GR) and guaiacol peroxidase (GPX) was found in sensitive cultivar HD 2987 compared to other two cultivars. Jasmonic acid was constitutively more in Kharchiya 65 while salicylic acid was maximally induced in HD 2987 indicating its higher susceptibility towards O3 stress. Modern cultivar HD 2987 suffered maximum oxidative stress and tried to overcome it by greatly enhancing antioxidative enzymes and also enzymes of the phenylpropanoid pathway (phenylalanine ammonia lyase, cinnamyl alcohol dehydrogenase and 4-coumarate CoA ligase) with subsequent induction of flavonoids and total phenolics; but ultimately suffered greatest decline in reproductive structures development and final yield. While in PBW 502 both enzymatic and non-enzymatic antioxidants played important role in combating O3 stress. Earlier released tolerant cultivar Kharchiya 65 manifested maximum increase in non-enzymatic antioxidants such as ascorbic acid, flavonoids, reduced glutathione along with jasmonic acid which offered resistance and probably rendered it most efficient in combating O3 stress. Further Kharchiya 65 showed high free radical scavenging activities compared to other cultivars. These findings will be useful for crop breeders to select O3 tolerant wheat cultivars for breeding purposes while developing cultivars for areas experiencing higher concentrations of O3.