The Mechanism Of Exogenous H₂S And JA Regulating The Growth Of Lateral Roots Of Rice Seedlings Under Drought Stress

Lateral root is an important part of root system in plants.The number and production speed of lateral roots are closely related to the efficiency of plants absorbing water and fertilizer.Therefore,studying the occurrence of lateral roots is an important way to understand the response of plants to the external environment and improve the survival rate of plant.Rice（Oryza sativa L.）is one of the most important food crops in China.Exploring the mechanism of rice seedlings response to drought stress provides a theoretical basis for agricultural production.Jasmonic acid（JA）is an important signaling molecule in plants.A large number of studies have confirmed that JAs improved the drought resistance of plants.Hydrogen sulfide（H₂S）,as the third gas signal molecule after nitric oxide（NO）and carbon monoxide（CO）,has also been proven to alleviate the effects of various biotic and abiotic stresses on the growth and development of plants.In this project,the rice seedlings with root length of 2cm were subjected to drought treatment.To explore the regulatory mechanism of exogenous H₂S and JA on the growth of lateral roots in rice seedlings under drought stress,the growth vigor of rice seedlings,the tip morphology of primary root and the occurrence of lateral root primordia,the expression level of H₂S synthase genes and their enzyme activity,the contents of endogenous H₂S and the expression level of lateral root development genes were observed.The results showed that:（1）Both the exogenous H₂S of 0.05 mmol·L^-1 and the exogenous JA of 0.25μmol·L^-1can increase the length and weight of primary roots,and the number of lateral roots in rice seedlings under drought stress,and promote the growth of underground and aboveground parts,thereby improving the overall growth of seedlings.（2）Exogenous H₂S and JA can upregulate the expression level of H₂S synthase genes LCD and DCD and the activity of their corresponding enzymes in the primary roots tips of rice seedlings under drought stress,which increase the content of endogenous H₂S in the root tips.The above effects of exogenous H₂S were not reversed by ibuprofen（IBU）,an inhibitor of JA synthesis,while the above effects of exogenous JA were reversed by hydroxylamine（HA）,an inhibitor of H₂S synthesis.Therefore,it is speculated that the exogenous JA plays the above role by inducing the synthesis of endogenous H₂S.（3）Exogenous H₂S and JA can upregulate the expression levels of lateral root development gene CYP2 and increase the number of lateral root primordia in rice seedlings under drought stress,resulting in promoting the occurrence of lateral roots.（4）Exogenous H₂S and JA raise the activities of superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）,and ascorbate peroxidase（APX）in the root tips of rice seedlings under drought stress,and reduce the content of H₂O₂,therefore,alleviating the oxidative damage caused by drought stress and improving the resistance against drought stress in rice seedlings.In summary,exogenous JA increases the content of endogenous H₂S by upregulating the genes expression level and activity level of endogenous H₂S synthase in the root tips of rice seedlings under drought stress,correspondingly,upregulating the expression level of lateral root development gene CYP2.Meanwhile,they removing excessive reactive oxygen species by upregulating the activity of antioxidant enzymes,then alleviating the growth of the primary and lateral roots in rice seedlings subjected to drought stress,finally improving the overall growth of the seedlings.