Seasonal Variations of Antioxidants in Wheat (Triticum aestivum) Leaves Grown Under Field Conditions

Abstract

Water-soluble antioxidants, glycolate oxidase activity and net photosynthesis were measured from seedling establishment to physiological maturity, in healthy, expanded, uppermost leaves collected weekly from wheat (Triticum aestivum L. cv. Yecora Rojo) plants growing under near-optimum field conditions. Most of the antioxidants fluctuated in a cyclic, non-regular manner throughout the season, the strongest oscillations being shown by glutathione and by H₂O₂ -scavenging enzymes. Time series analysis revealed significant correlation among the seasonal profiles of those antioxidants participating in the 'ascorbate-glutathione cycle'. Their seasonal changes were also synchronised with those of both midday maximal net CO₂ assimilation rate and of glycolate oxidase activity. This could confirm, over the whole of plant ontogeny and in field-grown plant material, the connections among photosynthetic activity and the plant cell antioxidant network and could suggest that similar mechanisms intervene in the integrated control of active oxygen generated during photorespiration. Peaks of antioxidant levels concentrated during certain periods of the plant growing season. Since no evidence of environmental stress was concurrently observed, it is suggested that a higher antioxidant capacity could be required in order to face endogenous and transient oxidative strain associated with definite plant developmental stages, namely juvenility, floral induction, stem elongation, anthesis and senescence.