Study On The Physiological And Biochemical Characteristics Of Glycyrrhiza Young Seedlings Responding In Drought Stress

Glycyrrhiza wa s an excellent ecological pioneer located in arid and semi-arid regions.Studying the physiological and biochemical characteristics of glycyrrhiza response to drought stress was an important part of revealing the mechanism of drought resistance of glycyrrhiza.The research results also provide the ultimate clarification of the drought resistance mechanism of plants,and at the same time provided an important basis for the establishment of reasonable drought-resistant cultivation patterns in production and breeding of drought-resistant varieties.In this study,3-month-old potted glycyrrhiza seedlings were used as materials,and drought stress was simulated by using different concentrations of PEG-6000（0%,5%,10%,15%,20%,25%）to soak the roots.By measuring the change in indicators of photosynthesischaracteristics,membranelipidperoxidation,osmotic adjustment substances and drought signal jasmonic acid which were closely related to drought,the physiological and biochemical response characteristics of drought resistance of glycyrrhiza were explored.The main results were as follows.（1）Under drought stress simulated by PEG-6000,the net photosynthetic rate（Pn）,intercellular carbon dioxide（Ci）,transpiration rate（Tr）,Stomatal conductance（Gs）and the content of chlorophyll of leaves of glycyrrhiza seedlings gradually increased treated with 5%,10%,and 15%PEG at the stress of 0-3h.Pn,Tr,Gs and the content of chlorophyll of leaves of glycyrrhiza seedlings began to gradually decline at the stress of 3-144h.Until the end of treatment,5%,10%PEG treatment was comparable to the control,and 15%PEG treatment was lower than the control.And Ci dropped first at3-6h,but started to rise at 6-144h.During the whole treatment period,the change trends of Pn,Tr,Gs,Ci and the content of chlorophyll of glycyrrhiza leaves treated with 20%and 25%PEG were the same as those under 5%,10%,and 15%PEG treatments,but the time was advanced.Pn,Tr,Gs,Ci,and the content of chlorophyll were significantly lower than those of the control at24-144h.Comparing all treatments at 3-144h,Pn,Tr,Gs and the contents of chlorophyll under the treatments of 5%,10%,and 15%were higher than those under the treatment of 20%and 25%.Ci increased again at 6-144h,probably due to the fact that the leaves of glycyrrhiza could not consume CO₂ in time,causing CO₂ to accumulate in large amounts in cells.This also showed that the main factor limiting the photosynthesis of glycyrrhiza seedlings was non-stomatal limitation.（2）Under different concentrations of PEG-6000 treatment,the contents of soluble sugar and free proline in leaves of glycyrrhiza under 5%,10%and15%PEG treatments accumulated in large amounts than the control at 0-48h,and gradually decreased at 48-144h.Soluble protein did not change significantly at 0-6h,6-24h gradually increased,increased significantly at24-144h.During the whole treatment period,the change trends of soluble sugar,free proline and soluble protein of glycyrrhiza leaves treated with 20%and 25%PEG were the same as those after 5%,10%,and 15%PEG treatment,but the time was advanced.（3）Under different concentrations of PEG-6000 treatment,the active oxygen in leaves of glycyrrhiza showed a bimodal trend,and reached two peaks at 6h and 72h.The content of MDA and the electrolyte permeability under 5%,10%,15%PEG-6000 concentration maintained at a low level at0-6h,and began to increase gradually from 6-144h.The contents of MDA and the electrolyte permeability under 20%,25%PEG-6000 were also maintained at low levels at 0-3h,and gradually increased at 3-144h.The activity of SOD and CAT increased gradually at 0-12h,and gradually decreased at 12-144h under 5%,10%,15%PEG treatment,and was comparable to that of the control until the end of treatment.Under the treatment of 5%,10%,and 15%PEG concentrations during the whole treatment period,the activity of POD appeared two peaks,reaching a large peak at 6h and another peak at 48h,and was comparable to the control level until the end of treatment.During the whole treatment period,the change trends of the activitiey of SOD,CAT and POD under the 20%and 25%treatments was the same as that under 5%,10%and 15%PEG treatments.The results showed that the three enzymes had different division of labor under drought stress.The antioxidant enzymes of SOD,POD,and CAT cooperated with each other in early stress,and H ₂O₂ was mainly cleared by POD and CAT during the late stress period.（4）Under 15%PEG concentration,the content of jasmonic acid increased slowly compared with the control at 0-3h,and rapidly increased at 0-3h.And it reached a maximum of 20.69 ug.g^-11 at 6h which increased by 934.50%compared with the control level and gradually decreased until the end of processing.The activity of LOX,AOS slowly increased at 0-3h,but rapidly increased at 3-6h,and reached the maximum at 6h.The maximum values were18.84 U.mg^-11 Pr.min^-1,19.84 U.mg^-11 Pr.min^-11 respectively.Compared with the control level,it increased 340.19%,and 506.73%,and then gradually decreased until the end of the treatment.Linolenic acid was a synthetic substrate for jasmonate.The content of linolenic acid showed a’V’curve.There was no significant difference at 0-3h compared with control,and then decreased rapidly.It reached a minimum value of 0.21mg.g^-11 at 6h,then began to rise to 0.37 mg.g^-11 at 12h which was 19.35%higher than that of the control.And then it gradually decreased until the end of the treatment and the end value was 0.31 mg.g^-1.The increase of enzyme activity was significantly lower than the increase of JA content.It was believed that the increase of JA content was partly due to the de novo synthesis pathway.