| Drought stress is one of the abiotic stress factors limiting sustainable development of agriculture.One of the research focuses is to enhance the drought resistance of plants by exogenous substance.Salicylic acid?SA?,considered as a signal molecule,regulates physiological functions of plants,and it also plays a vital role in improving the resistance of plants to non-biological stress.At present,the issues such as physiological mechanism of SA to improve the germination characteristics of plant seeds,the dose-effect and suitable concentration of SA to regulate plant drought resistance,the regulatory functions of SA on various physiological responses of plant seedlings under drought stress and the effect of SA on drought resistance of forage are needed to be further studied.Legume forage Coronilla varia is an excellent soil and water conservation plant,but drought is an crucial factor limiting its planting extensively.Furthermore,the research on Coronilla varia sprayed with exogenous compounds to improve the drought resistance is almost blank.This research investigated the effects of SA on seed germination and plant growth,water status,photosynthesis,antioxidant metabolism,osmotic regulation of Coronilla varia?cultivar“Lvbaoshi”?leaves under drought stress.The author aimed at exploring the regulation effects and mechanism of exogenous SA on drought resistance of Coronilla varia under drought stress.The main results and conclusions are as follows:1.Seeds soaked with 0.5-1mmol·L-1SA significantly increased proline?Pro?,soluble protein?SP?contents and the activities of amylase?AMS?,catalase?CAT?,peroxidase?POD?,superoxide dismutase?SOD?and ascorbic acid oxidase?APX?of Coronilla varia seeds.Cell electrolyte permeability,starch content and soluble sugar?SS?content of Coronilla varia seeds were significantly decreased by seeds soaked with 1 mmol·L-1SA.Seeds soaking with SA had no significant effect on contents of malondialdehyde?MDA?,glutathione?GSH?,and glutathione reductase?GR?activity of Coronilla varia seeds.2.Under drought stress,germination percentage,vigour,index and vitality index of Coronilla varia seeds were significantly decreased,and germs growth,osmotic regulation,protein synthesis and antioxidant metabolism of Coronilla varia were also inhibited.0.5-1mmol·L-1SA significantly increased germination percentage,vigour,germination index,vitality index and bud length of Coronilla varia.Under the stress of 12%PEG,the dry mass of Coronilla varia germs processed by 1mmol·L-1SA were significantly higher.0.5-1mmol·L-1SA processing significantly increased Pro and SP content,activities of CAT,POD and SOD of Coronilla varia germs under drought stress,while cell electrolyte permeability,H2O2 content and O2-·production rate of germs were significantly decreased and 1mmol·L-11 SA produced the best results.It was concluded that SA could effectively faciliate seed germination and germ and alleviate the inhibition effects of drought stress on seed germination of Coronilla varia by improving osmotic regulation?osmotic regulation,antioxidation,activate amylase and decrease the cell membrance lipid peroxidation of the seed and germ of Coronilla varia3.The plant height and leaf area of Coronilla varia seedlings were less than CK at the late stage of drought stress,meanwhile leaf water content was decreased and the growth of seedlings was inhibited.Spraying with 0.5-1mmol·L-11 SA significantly increased plant height,leaf area,leaf relative water content and moisture content,and contents of SS,Pro,SP and Ca2+of Coronilla varia leaves under drought stress.However,spraying with 0.5-1mmol·L-11 SA significantly decreased leaf water saturation deficit.It was concluded that SA could promote Coronilla varia to accumulate osmotic adjustment substance in order to improve osmotic regulation ability,maintain the normal osmotic pressure and keep water absorbing ability and water retaining capacity of leaves.In this way SA can mitigate the damage from drought stress to the growth and water physiology of Coronilla varia.4.Under drought stress,chlorophyll and carotenoid contents gradually decreased in Coronilla varia leaves,and net photosynthetic rate?Pn?,stomatal conductance?Gs?,transpiration rate?Tr?and water use efficiency?WUE?of Coronilla varia leaves were significantly decreased,but the intercellular CO2 concentration?Ci?,stomatal limitation value?Ls?were significantly increased.Meanwhile,the maximal photoche-mical efficiency?Fv/Fm?,actual photochemical efficiency(?PS?),photochemical quenching coefficient?qP?,photochemical reaction of PS??P?were decreased significantly as the stress duration extended and the stress degree increased,and the photosystem?excitation pressure?1-qP?,non-photochemical quenching coefficient?NPQ?were observably increased.After 11 days of drought stress,0.5-2mmol·L-1SA treatments significantly increased total chlorophyll and carotenoid contents,gas exchange parameters and WUE,but decreased the Ls of leaves.Fv/Fm,?PS?,qP,P of leaves were much higher while the?1-qP?and NPQ were lower than those under drought treatment,with 1mmol·L-1 as the most effective SA concentration.The results showed that under drought stress,SA could retard chlorophyll degradation,stabilize the structure and function of PS?reaction center,enhance gas exchange ability and improve light energy capture,transformation and utilization efficiency of Coronilla varia leaves.and thereby decreased the decline of photosynthesis caused by droughts.5.Under drought stress,the O2-·production rate,H2O2,MDA and ASA contents,cell membrane permeability of Coronilla varia leaves significantly increased,but GSH content obviously decreased.The activities of CAT,POD and SOD in leaves increased first and then decreased as the drought stress extended.At concentration of0.5-2mmol·L-1,SA decreased the O2-·production rate,H2O2 and MDA contents,cell membrane permeability,and increased the antioxidant enzyme activities of CAT,POD and SOD.However,SA did not affect the ASA and GSH contents in seeding leaves at these concentrations.These results demonstrated that intracellular reactive oxygen species rapidly accumulated under drought stress,resulting in membrane lipid peroxidation,membrane structure disruption,and electrolyte extravasation of cells,suggesting that exogenous SA could improve drought resistance of Coronilla varia by reducing reactive oxygen levels,increasing the activity of the antioxidant system,and alleviating oxidation damage to cell membranes under drought stress due to drought-induced membrane lipid peroxidation.The most effective concentration of SA was 1 mmol·L-1. |
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