SEASONAL-VARIATIONS OF ANTIOXIDANTS IN WHEAT (TRITICUM-AESTIVUM) LEAVES GROWN UNDER FIELD CONDITIONS

Water-soluble antioxidants, glycolate oxidase activity and net photosy nthesis were measured from seedling establishment to physiological mat urity, in healthy, expanded, uppermost leaves collected weekly from wh eat (Triticum aestivum L. cv. Yecora Rojo) plants growing under near-o ptimum field conditions. Most of the antioxidants fluctuated in a cycl ic, non-regular manner throughout the season, the strongest oscillatio ns being shown by glutathione and by H2O2-scavenging enzymes. Time ser ies analysis revealed significant correlation among the seasonal profi les of those antioxidants participating in the 'ascorbate-glutathione cycle'. Their seasonal changes were also synchronised with those of bo th midday maximal net CO2 assimilation rate and of glycolate oxidase a ctivity. This could confirm, over the whole of plant ontogeny and in f ield-grown plant material, the connections among photosynthetic activi ty and the plant cell antioxidant network and could suggest that simil ar mechanisms intervene in the integrated control of active oxygen gen erated during photorespiration. Peaks of antioxidant levels concentrat ed during certain periods of the plant growing season. Since no eviden ce 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 pla nt developmental stages, namely juvenility, floral induction, stem elo ngation, anthesis and senescence.