Dose dependent differential effects of toxic metal cadmium in tomato roots: Role of endogenous hydrogen sulfide.

In this study, hydroponic experiments were conducted to elucidate mechanism(s) that are associated with differential effects of low (5 μM) and high (25 μM) dose of cadmium (Cd) stress in tomato. Furthermore, emphasis has also been focused on any involvement of endogenous hydrogen sulfide (H2S) in differential behaviour of low and high doses of Cd stress. At low dose of Cd, root growth i.e. root fresh weight, length and fitness did not significantly alter when compared to the control seedlings. Though at low dose of Cd, cellular accumulation of Cd was slightly increased but this was accompanied by higher endogenous H2S and phytochelatins, L-cysteine desulfhydrase (DES) activity, activities of glutathione biosynthetic and AsA-GSH cycle enzymes, and maintained redox status of ascorbate and glutathione. However, addition of hypotaurine (HT, a scavenger of H2S) resulted in greater toxicity, even at low dose of Cd, and these responses resembled with higher dose of Cd stress such as greater decline in root growth, endogenous H2S and phytochelatins, activities of DES, glutathione biosynthesis and AsA-GSH cycle enzymes, disturbed redox status of ascorbate and glutathione which collectively led to higher oxidative stress in tomato roots. Moreover, addition of HT with higher dose of Cd also further enhanced its toxicity. Collectively, the results showed that differential behaviour of low and high dose of Cd stress is mediated by differential regulation of biochemical attributes in which endogenous H2S has a crucial role.