The participation of nitric oxide in hydrogen sulphide-mediated chromium tolerance in pepper (Capsicum annuum L) plants by modulating subcellular distribution of chromium and the ascorbate-glutathione cycle

Abstract

The promising response of chromium-stressed (Cr(VI)–S) plants to hydrogen sulphide (H2S) has been observed, but the participation of nitric oxide (NO) synthesis in H2S-induced Cr(VI)–S tolerance in plants remains to be elucidated. It was aimed to assess the participation of NO in H2S-mediated Cr(VI)–S tolerance by modulating subcellular distribution of Cr and the ascorbate-glutathione (AsA-GSH) cycle in the pepper seedlings. Two weeks following germination, plants were exposed to control (no Cr) or Cr(VI)–S (50 μM K2Cr2O7) for further two weeks. The Cr(VI)–S-plants grown in nutrient solution were supplied with 200 μM sodium hydrosulphide (NaHS, donor of H2S), or NaHS plus 100 μM sodium nitroprusside (SNP, a donor of NO). Chromium stress suppressed plant growth and leaf water status, while elevated proline content, oxidative stress, and the activities of AsA-GSH related enzymes, as well as endogenous H2S and NO contents. The supplementation of NaHS increased Cr accumulation at root cell walls and vacuoles of leaves as soluble fraction to reduce its toxicity. Furthermore it limited oxidative stress, improved plant growth, modulated leaf water status, and the AsA-GSH cycle-associated enzymes’ activities, as well as it further improved H2S and NO contents. The positive effect of NaHS was found to be augmented on those parameters in the CrS-plants by the SNP supplementation. However, 0.1 mM cPTIO, the scavenger of NO, inverted the prominent effect of NaHS by decreasing NO content. The supplementation of SNP along with NaHS + cPTIO reinstalled the positive effect of NaHS by restoring NO content, which suggested that NO might have a potential role in H2S-induced tolerance to Cr(VI)–S in pepper plants by stepping up the AsA-GSH cycle.