Hydrogen Sulfide Signal Improves Drought Tolerance Of Millet By Regulating Antioxidant System

With the change for global climate,the impact of drought is becoming increasingly serious.Shanxi is located in the Loess Plateau,and drought has always been the most serious meteorological disaster in Shanxi Province.Millet is a characteristic minor cereal in Shanxi province,which has strong drought and barren resistance,and is becoming a important material for studying the resistance mechanism of Gramineae crops.Hydrogen sulfide（H₂S）is the third gasotransmitter.Physiological concentrations of H₂S can regulate various physiological responses in plants,and it is widely involved in the process of plants responding to abiotic stresses.Therefore,exploring how H₂S signals participate in the drought resistance process of millet,thereby improving its drought resistance,is of great significance for in-depth understanding of the drought resistance mechanism of H₂S signals,exploring drought resistance pathways for crops,and promoting dryland crop production.It also provides a theoretical basis for the research and development of new plant drought resistance agents based on H₂S signals.In this study,Jingu 21 was selected as the test material to analyze the effects of different H₂S levels on the growth and development,photosynthetic system,and antioxidant system of millet seedlings under drought stress.Trough transcriptome analysis,the mechanism of H₂S signal improving the drought tolerance of millet was further explored.The main research results are as follows:1.Exogenous H₂S promoted the growth and development of millet seedlings under drought stress.Compared with the drought treatment group,100μM sodium hydroxide（H₂S donor）significantly improved the germination potential,germination rate,vigor index,germination index,germ length,plant height and D value of seeds.Seedling height and maximum leaf area per plant increased significantly.The total root length,root tip mitotic index and lateral root number of millet seedlings increased significantly The above results indicated that H₂S signal promoted millet seed germination,seedling growth and root development under drought stress.2.Exogenous H₂S improved the photosynthetic performance of millet seedlings under drought stress.Under drought stress,100μM Na HS significantly increased the dry weight of aboveground and underground parts of seedlings,significantly decreased the root-shoot ratio,and significantly increased the contents of soluble sugar and soluble protein.Significantly increased leaf area,dry weight and specific leaf weight per plant;And some photosynthetic pigment content and photosynthetic parameters were significantly improved.The above results indicated that H₂S promoted photosynthesis of millet seedlings under drought stress.3.Exogenous H₂S enhanced the antioxidant capacity of millet seedlings under drought stress.Under drought stress,100μM Na HS treatment significantly improved the growth level of millet seedlings.The antioxidant content and antioxidant oxidase activity of seedlings were significantly increased,resulting in a signifcant decrease in the accumulation of malondialdehyde（MDA）,hydrogen peroxide（H₂O₂）and superoxide anion（O₂·^–）thus alleviating the damage degree of the seedlings.The above results indicated that H₂S signal improved the antioxidant capacity of millet seedlings under drought stress.4.Transcriptome analysis of the mechanism of exogenous H₂S improving drought tolerance in millet.Under drought stress,the differentially expressed genes of millet seedlings were closely related to photosynthesis and antioxidant system after exogenous H₂S treatment.We further conducted hierarchical cluster analysis on the significantly enriched antioxidase coding genes,and found that H₂S signal had an impact on the expression of major antioxidant enzymes at the transcription level.Six candidate genes were selected and verified by q RT-PCR which confirmed that H₂S signal was involved in regulating the expression of genes encoding antioxidant enzymes under drought stress,which deepened our understanding of the mechanism of H₂S signal regulating the stress resistance of millet seedlings.In summary,the signaling molecule H₂S helps to improve the growth and development,photosynthesis and antioxidant capacity of millet seedlings under drought stress.Transcriptome sequencing further revealed that H₂S signaling can affect the expression of genes encoding antioxidant enzymes millet seedlings at the transcription level,improving the ability of millet seedlings to resist drought stress.