Nitrate-mediated maintenance of photosynthetic process by modulating hypoxic metabolism of common bean plants

Abstract

Nitrate has been reported to improve tolerance of plants under flooding by modulating carbon and nitrogen metabolism of root cells; however, the extent to which nitrate modulates the photosynthetic process is not well understood. This work aimed to evaluate the photosynthetic process by nitrate-mediated modulation of hypoxic metabolism in the root of common bean plants (Phaseolus vulgaris L.) under flooding and recovery conditions. Three groups of common beans [N2-fixing (N2)], N2-fixing pre-hypoxic nitrate-treated (N2 + NO3−), and nitrate (NO3−)-supplied plants] were grown in vermiculite and the root system was subjected to flooding for 48 h at the early reproductive stage. After flooding, plants returned to normoxic conditions per 24 and 72 h for recovery. Plants from N2 + NO3− and mainly NO3− groups maintained transpiration rate (E) and CO2 assimilation under root-flooding, which was not shown by N2-fixing plants. No changes in the dynamic dissipation of photosynthetic energy were evidenced in leaves of NO3− plants upon flooding, besides an increase in nitrate reductase (NR) activity and a decrease in fermentative enzymes in roots. Reactive oxygen species (ROS) and antioxidative enzymes increased in leaves and decreased in roots. Nitrate-mediated maintenance of the photosynthetic process may be related to induction in NR activity in roots to alleviate the toxic effects of fermentation through a decrease of fermentative enzyme activity.