Ascorbate and Hydrogen Peroxide Modify Metabolite Profile of Wheat Differently

Effects of ascorbate (ASA) and hydrogen peroxide (H 2 O 2 ) on metabolite profile was compared in wheat. Interestingly, the redox environment became more oxidized after ASA treatment and more reduced after H 2 O 2 addition based on the ratios of oxidised and reduced ascorbate and glutathione. The excess of ASA could inhibit, while H 2 O 2 could induce the oxidative pentose phosphate pathway producing reducing power as shown by the unchanged and decreased glucose-6-phosphate content, respectively. This different effect on glucose-6-phosphate content can also explain the reduced formation of several amino acids from the intermediate products of glycolysis after ASA treatment and their constant or greater levels after H 2 O 2 addition. In contrast to most amino acids, the accumulation of Pro was greatly induced by ASA, and this change was fivefold greater than after H 2 O 2 addition. This difference could also contribute to the distinct redox shifts after the two treatments, since NADPH is oxidised during Pro synthesis. The more oxidising environment after ASA treatment activated several transcripts related to the ascorbate–glutathione cycle and the pentose phosphate pathway. Our results indicate the overcompensating effect of ASA and H 2 O 2 on the redox environment in leaf tissues and the subsequent different adjustment of metabolite profile and the related transcript levels.