Signaling Mechanism Of Hydrogen Sulfide Regulating Seed Germination And Seedling Growth In Plant Under Cadmium And Drought Stresses

Cadmium (Cd) has toxic effects on wheat growth. Effects of hydrogen sulfide (H2S) donor, sodium hydrosulfide (NaHS) on the germination and activities of hydrolytic enzymes in wheat (Triticum aestivum L.) seeds were researched. Treatment with NaHS promoted imbibition and germination of wheat seeds in a dose-dependent manner; whereas little visible symptom was observed in germinating seeds and radicle tips cultured in NaHS solutions. It was verified that H2S or HS-rather than other sulfur-containing components, derivation of NaHS exhibit its potential role in promoting seed germination against Cd stress. Further studies showed that NaHS could promote amylase and esterase activities, reduce Cd-induced disturbance of plasma membrane integrity in the radicle tips, and sustain lower levels of·O2-,H2O2 and malondialdehyde(MDA) in germinating seeds. Furthermore, NaHS pretreatment increased activities of peroxidase(POD),superoxide dismutase(SOD),catalase(CAT) and acorbate peroxidase(APX) and inhibited that of lipoxygenase(LOX). Similar results were found in soybean seedlings under drought-induced oxidative stress.Alternatively, NaHS promoted the accumulation of free amino acids in seeds exposed to Cd. In addition, a rapid accumulation of endogenous H2S in seeds was observed at the early stage of germination, and higher level of H2S in NaHS-pretreated seeds. These data indicated that H2S was involved in the mechanism of germinating seeds'responses to Cd stress.In addition, we also found that soybean (Glycine max L.) seedlings sprayed with exogenous H2S donor NaHS prolonged the longer survival time of life, and enlarged higher biomass of both leaf and root than in non-sprayed controls under continuous drought stress. With the continuous drought stress, the content of chlorophyll in the leaves of both Xu-1 and Xu-6 cult.ivar of soybean decreased dramatically. The drought-induced decrease in chlorophyll could be alleviated by spraying H2S donor. It was also shown that spraying with H2S donor dramatically retained higher activities of SOD, CAT and LOX, delayed excessive accumulation of MDA, H2O2, and·O2- compared with the control. These results suggest that H2S can increase drought tolerance in soybean seedlings by acting as an antioxidant signal molecule for the response.