Mechanism Of Exogenous Acetic Acid-regulated Root Growth In The Rice Seedlings Subjected To Drought Stress

The root is the organ that absorbs water and inorganic salts in plant.It is known that drought is the main abiotic stress factor that hinders the normal growth and development of plants.Among a plant,the root is the first organ to be affected in the plant exposed to drought stress.Rice?Oryza sativa L.?is one of the most important food crops in China.It is important for the subsequent growth and development to relieve and reverse the effects of drought stress on rice seedlings.Furthermore,it has been proved that jasmonics?JAs?can be used as defense signaling molecules to participate in stress response to drought stress in plants.Importantly,recent studies suggested that acetic acie?HAc?may improve plant drought tolerance through triggering jasmonic acid?JA?signaling pathway or abscisic acid?ABA?signaling pathway.To explore the mechanism of exogenous HAc in regulating the root growth of rice seedlings under drought stress.In present study,rice seedlings were treated with 20%PEG at the stage of one-leaf-one-plant,then we investigated the differences of growth index,anatomical structure of root tip and antioxidant metabolism level among different treatments,as well as the changes of gene expression levels of key enzymes and their activity levels,and JA content in the process of JA biosynthesis.The results showed that:?1?Exogenous HAc significantly reduced the accumulation of superoxide anion(O₂^?-)and hydrogen peroxide?H₂O₂?,and decreased the relative permeability of the plasma membrane in the root tip of seedlings,thus promoted the growth of rice seedlings under drought stress.Moreover,the effect of HAc is inversely proportional to the concentration of HAc.?2?Exogenous HAc significantly decreased the contents of H₂O₂and malondialdehyde?MDA?,and the relative permeability of the plasma membrane through increasing the gene expression levels and activities of superoxide dismutase?SOD?,peroxidase?POD?,catalase?CAT?and ascorbate peroxidase?APX?in the roots of rice seedlings under drought stress,resulting in alleviating the damage caused by drought stress on rice seedlings and improving their resistance against drought stress.?3?In a specified time,exogenous HAc and JAs up-regulated the expression levels of Os HI-LOX and Os AOS2 in the root tips of rice seedlings under drought stress,and significantly increased the activity of lipoxygenase?LOX?and the content of JA.However,the above effects of HAc and Me JA were reversed by ibuprofen?IBU?,a synthesis inhibitor of JA.This result revealed that HAc and Me JA can induce the production of endogenous JA.?4?Exogenous HAc and JAs raised the cell activity of primary root tip in the rice seedlings under drought stress,and delayed the appearance of root tip vessels and the downward movement of lateral roots,so as to inhibit the shortening of root tips and ultimately promoted the growth of primary roots.Whereas the effects of HAc and methyl jasmonate?Me JA?were reversed by IBU.Therefore,it is inferred that exogenous HAc exerts the above effects through inducing the synthesis of JA.?5?Both of exogenous HAc and JAs shortened the length of adventitious roots in the rice seedlings subjected to drought stress,while promoted the occurrence and growth of lateral roots in adventitious roots.However,the JA synthesis inhibitor IBU significantly promoted the length of adventitious roots in the rice seedlings under drought stress,and inhibited the growth of lateral roots in adventitious roots.It suggesting that the production of endogenous JA in the root tips of rice seedlings not only inhibited the elongation of adventitious roots,but also promoted the growth of lateral roots under drought stress.?6?Exogenous HAc accelerated the growth of the underground part and above ground part of the seedlings by inducing the synthesis of JA in the root tips of rice seedlings subjected to drought stress,so as to improve the overall growth of the seedlings.In summary,exogenous HAc can induce the JA synthesis of root tips in the rice seedlings under drought stress,and then increase the levels of gene expression and activity in antioxidant enzymes,thus reduce the damage to the cells in root tips.Furthermore,exogenous HAc delays the vessel generation of primary roots and the down migration growth of lateral roots,resulting in improving the elongation of primary roots under drought stress.Ultimately,exogenous HAc-induced JA promotes the roots growth of rice seedlings subjected to drought stress.