Hydrogen sulfide regulates NaCl tolerance in brinjal and tomato seedlings by Na+/K+ homeostasis and nitrogen metabolism

In the present study, hydroponic experiments were performed to explore the mechanistic role of H2S (NaHS (donor of H2S); 40 mu M) in alleviating NaCl stress in brinjal and tomato seedlings by analyzing the growth, pigments content, gas exchange parameters, and contents of inorganic nitrogen and activities of enzymes involved in N2 metabolism. While NaCl at 20 mM declined the growth (tolerance index (TI) and plant height), pigment content (total chlorophyll and Chl a/b), and gas exchange parameters (intercellular CO2 concentration; Ci, net photosynthetic rate; A, transpiration rate; E, stomatal conductance; Gs). It also variably affected the inorganic N (NO3-, NO2- and NH4+) content, and the enzymes involved in nitrate (nitrate reductase; NR and nitrite reductase; NiR), and ammonium (glutamine synthetase; GS, glutamate synthase; GOGAT and Glutamate dehy-drogenase; GDH) assimilation, whereas the supplementation of H2S showed considerable improvement in all the studied parameters. Furthermore, the addition of H2S scavenger hypotaurine (HT; 200 mu M) to NaCl + NaHS seized all the recovery on the above parameters caused by the NaHS treatment, suggesting the role of exogenous H2S. While, the addition of an inhibitor of H2S generation propargylglycine (PAG; 100 mu M) to NaCl treatments further declined the growth more than NaCl treatment alone, implying the role of endogenous H2S. Altogether, our study highlights the modulatory role of endogenous and exogenous H2S in conferring NaCl stress tolerance in brinjal and tomato seedlings by maintaining the ion homeostasis and the C/N ratio.