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

Soil mercury (Hg) contamination is a major factor that affects agricultural yield and food security. Hydrogen sulfide (H2 S) plays multifunctional roles in mediating a variety of responses to abiotic stresses. The effects of exogenous H2 S 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 H2 S) 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, H2 S 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). H2 S might act as an antioxidant to inhibit or scavenge reactive oxygen species (ROS) productions for maintaining the lower MDA and H2 O2 levels, and thereby preventing oxidative damages. All these results indicated H2 S effectively alleviated Hg toxicity by sequestering it in roots or by regulating ROS in seedlings and then thus significantly promoted rice growth.