Biochemical responses of thiourea in ameliorating high temperature stress by enhancing antioxidant defense system in wheat

In this study, effect of exogenously applied thiourea (TU, 6.6 mM) and dithiothreitol (DTT, 0.07 mM) as seed pretreatment or as foliar spray (at 90 days after sowing) in two wheat (Triticum aestivum L.) cvs. C 306 (heat tolerant) and PBW 343 (heat susceptible) at seedling and reproductive stages under high temperature (HT) stress was investigated. The heat tolerant cv. C 306 exhibited much lower membrane injury index (MII), thiobarbituric acid reactive substances (TBARs) and H₂O₂ contents, but such effect was not accompanied by higher activities of the enzymes involved in the reactive oxygen species scavenging system during both developmental stages. Application of TU under HT reduced MII and TBARs and H₂O₂ contents, but as a rule did not affect activities of antioxidant enzymes. Therefore pretreatment by TU/DTT, no doubt, improved the resistance against oxidative stress through increase in membrane stability parameters but their effect on antioxidant enzymes was not apparent under the prevailing conditions of the experiment.