Hydrogen sulfide alleviates mercury toxicity by sequestering it in roots or regulating reactive oxygen species...

Soil mercury (Hg) contamination is a major factor that affects agricultural yield and food security. Hydrogen sulfide (H₂S) plays multifunctional roles in mediating a variety of responses to abiotic stresses. The effects of exogenous H₂S on rice (Oryza sativa var 'Nipponbare') growth and metabolism under mercuric chloride (HgCl₂) stress were investigated in this study. Either 100 or 200 μM sodium hydrosulfide (NaHS, a donor of H₂S) pretreatment improved the transcription of bZIP60, a membrane-associated transcription factor, and then enhanced the expressions of non-protein thiols (NPT) and metallothioneins (OsMT-1) to sequester Hg in roots and thus inhibit Hg transport to shoots. Meanwhile, H₂S promoted seedlings growth significantly even in the presences of Hg and superoxide dismutase (SOD, EC 1.15.1.1) or catalase (CAT, EC 1.11.1.6) inhibitors, diethyldithiocarbamate (DDC) or 3-amino-1,2,4-triazole (AT). H₂S might act as an antioxidant to inhibit or scavenge reactive oxygen species (ROS) productions for maintaining the lower MDA and H₂O₂ levels, and thereby preventing oxidative damages. All these results indicated H₂S effectively alleviated Hg toxicity by sequestering it in roots or by regulating ROS in seedlings and then thus significantly promoted rice growth.