Sulfur-mediated control of salinity impact on photosynthesis and growth in mungbean cultivars screened for salt tolerance involves glutathione and proline metabolism, and glucose sensitivity

Two mungbean (Vigna radiata L.) cultivars, namely, Punt Mung (salt-tolerant) and Samrat (salt-sensitive), were tested for their response to salinity (50mM NaCl) and sulfur (1.0mM SO42- and 2.0mM SO42-) supplied alone or in combination. Compared to Punt Mung, the extent of 50mM NaCl-accrued decreases in leaf gas exchange parameters (net photosynthetic rate, intercellular CO2, stomatal conductance, intrinsic water-use efficiency and Rubisco activity), stomatal behavior (frequency and diameter), and plant dry mass was higher in Samrat. However, contents of proline and reduced glutathione (GSH), and the activity of glutathione reductase (GR) and nitrate reductase (NR) were higher in Punt Mung. Notably, the salt-sensitive Samrat exhibited the higher content of glucose and activity of proline oxidase under 50mM NaCl exposure. The effects of 2.0mM SO42- in alleviating 50mM NaCl impact on leaf gas exchange parameters and plant dry mass were more conspicuous in Punt Mung. Overall, SO42- helped Punt Mung to maintain higher cellular levels of GSH and proline; a higher activity of GR and NR; decreased activity of proline oxidase, lower content of glucose, and controlled stomatal behavior. Eventually, SO42--mediated aforesaid changes culminated into a higher tolerance of Punt Mung to 50mM NaCl stress when compared to Samrat. Thus, the strategy of sulfur-mediated control of salinity in V. radiata may be adopted for salinity prone areas.