Elucidating the role of exogenous iron (Fe) in regulation of hydrogen sulphide (H2S) biosynthesis and its concomitant effect on seedling growth, pigment composition and antioxidative defense in NaCl stressed tomato seedlings

There is a paucity of information on the role of iron nutrition in regulating H₂S-mediated salinity tolerance in plants. The present work implies exogenous Fe and Na₂S (H₂S-donor) for investigating the interactive effects of Fe and H₂S in regulating seedling growth, osmolyte accumulation, chlorophyll accumulation and antioxidative defense under salinity stress. To achieve this, an experiment was set up with seeds of tomato (Solanum lycopersicum L. var. romeo) grown in presence of NaCl concentration (80 mM). Control seedlings were grown using half strength hoagland nutrient solution without NaCl. Exogenous Fe (100 µM) and H₂S was supplied in the form of Na₂S (100 µM) individually and in combination both in presence and absence of NaCl. Growth parameters like shoot length and root lengths were taken along with chlorophyll, osmolyte contents, enzymatic and non-enzymatic antioxidants as well as content of H₂S and L-DES activity were also measured. Results demonstrated that exogenous Fe and H₂S to an extent provide protection to tomato seedlings subjected to salt stress through prevention membrane damage, increased antioxidative defense and there was significant increase in L-DES activity that led to increased H₂S content. Exogenous Fe and Na₂S application in tomato seedlings under salt stress exhibited decrease in malondialdehyde content by 19% and 50% respectively and H₂O₂ by 13.7% and 16.8% respectively. Combined application of Fe and Na₂S increased the levels of antioxidative enzyme activities including CAT (53.8%), POX (14%), SOD (58%) and APX (11.7%) was observed under salt stress. However, tomato seedlings supplemented with combined application of Fe and H₂S showed decreased H₂S content as well as lower L-DES activity. Simultaneously, combined application of Fe and H₂S to salt stressed tomato seedlings however showed increased activity of some of the antioxidative enzymes deciphering positive role of this interaction of Fe and Na₂S under the influence of salt stress.