The Effect of Habitat Conditions on the Activity of Enzymes and Content of Metabolites of the Ascorbate-Glutathione Cycle in Plantago media Leaves

Abstract

The ascorbate-glutathione cycle (AGC) is a metabolic pathway that detoxifies H2O2, which is a reactive oxygen species produced as a waste product in metabolism. The cycle involves the antioxidant metabolites – ascorbate, glutathione, and NADPH, as well as enzymes linking them. We studied the effect of habitat conditions on the activity of enzymes and contents of metabolites of the ascorbate-glutathione cycle in Plantago media leaves. The experimental plants grew on the floodplain meadow: on the sparsely vegetated coastal edge (Site 1) and in the grass stand in the central part of the meadow (Site 2). The hoary plantain plants growing in Site 1 received twice more light than the plants in Site 2. The ascorbate and glutathione concentrations in leaves of the well-lit plants were 2–3 times higher than in shaded plants. The maximal levels of these metabolites were observed at midday, when light intensity and air temperature were increased, and relative humidity was decreased. The activity of AGC enzymes was changing similarly to the metabolite contents. As a result, the leaves of hoary plantain plants from the sites with different light levels did not significantly differ in their hydrogen peroxide concentrations. Our data suggest that the environmental conditions and, above all, the light intensity fine-tune the operation of AGC in plant leaves