Abstract
Nitric oxide (NO), a signaling molecule with diverse physiological functions, improves immunity of the plant against different environmental stresses. Heavy metal stress-induced structural and functional damages in cells are common consequences. Seed germination and seedlings development are crucial phases in the life cycle of a plant. The present experiment was designed to investigate how NO suppresses hexavalent chromium Cr(VI)-provoked impairment in the key processes during seed germination and seedlings development of tomato. This study reports that Cr(VI) stress significantly impaired seed germination attributes and the activity of hydrolyzing enzymes, such as alpha-amylase (alpha-A) and protease (Pr). However, exogenous NO donor sodium nitroprusside substantially improved seed germination parameters and upregulation of alpha-A and Pr. Furthermore, NO improved the content of nitrogen (N), NO, and proline (Pro), and modulated the activity of enzymes involved in Pro and N-assimilation. Under Cr(VI) toxicity conditions, NO improved the content of metal ligation compounds (non-protein thiols and total thiols), ascorbate and glutathione (GSH), and maintained higher content of GSH in glutathione pool (GSH:GSSG) and suppressed the formation of 4-hydroxy-2-nonenal and protein carbonylation, and electrolyte leakage. It may be concluded that NO improved the activity of hydrolyzing and Pro and N-metabolism enzymes. Application of NO also enhanced non-enzymatic antioxidants, and 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity under Cr(VI) toxicity conditions, thereby improved enhanced seed germination and seedlings vigor.