| Astragalus membranaceus(Fisch.)Bunge.is a traditional Chinese medicine and its roots are used as medicine.The A.membranaceus is mainly produced in the northeast,north and northwest of China,and the astragalus saponin is one of the main active ingredients.The content of saponins in different area varies greatly,and this difference is affected by environmental factors and genetic factors.The water factor is one of the important ecological factors affecting the secondary metabolism of A.membranaceus.Moderate water regulation can promote the accumulation of A.membranaceus.However,the molecular ecological mechanism of the quality of A.membranaceus has not been clarified under water regulation.Therefore,in this study,the water regulation experiment of potted A.membranaceus was carried out,and the study on the response regulation of saponin to water regulation was systematically carried out.The mechanism of water regulation affecting the formation of saponin was explained,which provided theoretical support for the precise cultivation of A.membranaceus.In this study,the pot experiment was conducted and the A.membranaceus was used as the research material.According to the precipitation situation of the growth area of A.membranaceus,the water-rich group was set up,and the water regulation mode of short-term asymptotic drought and long-term water deficit was adopted respectively.The biomass,saponin content,gene expression and nutrient status of cultivated soil in the process of water regulation were investigated.The effect of soil conditions on the secondary metabolism of saponins in the membrane was analyzed under water control.The main findings were as follows:1.Effects of different water regulation modes on the growth and development and active ingredients of A.membranaceusThe short-term water control,the dry weight of aboveground and underground tissues of A.membranaceus in the asymptotic drought group was lower than that of the water-rich group,and the dry matter weight was reduced.The contents of astragaloside IV and total saponins of A.membranaceus in the asymptotic drought group reached the maximum on the 15 th day after treatment,and increased by 16.8% and 23.6% in the relatively the water-rich group,respectively.At the same time,the accumulation of astragaloside IV and total saponins of in the asymptotic drought group reached the maximum,which was 1.37 and 1.45 times of the water-rich group.The long-term water control,the fresh weight and dry weight of the aboveground tissues of A.membranaceus in the water deficit group were only 57.62% and 55.92%.But the fresh weight and dry weight of underground tissues of A.membranaceus were higher than that of the water-rich group.The content of astragaloside IV and total saponin in water deficit group reached the maximum in July and August,respectively,which was 15.92% and 49.42% higher than that in the water-rich group.In the middle of July,the accumulation of astragaloside was the highest,which was 2.14 times that of the water-rich group.Both short-term and long-term water regulation promoted the accumulation of astragalus saponin,and long-term water deficit promoted the accumulation of total saponins in A.membranaceus.Therefore,the use of water deficit in July and August may be an effective means to regulate the quality of A.membranaceus.2.Effects of different water regulation modes on the relative expression of key enzyme genes in the synthesis pathway of astragalus saponinsThe short-term water control,the expressions of AACT,HMGS,IDI,FPS,SS and SE in the moderate drought group were significantly lower than those in the water-rich group,but the expression in the severe drought stage was higher than that in the water-rich group.The expression of HMGR was significantly affected after rehydration,and the decrease was significant.The expression of CAS decreased gradually during the drought stage.The key enzymes had high correlations between genes and respond to changes in soil moisture.In the long-term water regulation process,the expression patterns of AACT,IDI,FPS and CAS in the water deficit group were similar.At the end of June,the relative expression of genes was significantly greater than that of the well-rich group,reaching a maximum in mid-July.The expression levels of HMGS,SS and SE of the water deficit group in mid-July were significantly higher than those in the water-rich group.Under long-term water control,the expression levels of astragaloside IV and AACT,HMGS,IDI,FPS,SS,SE and CAS were significantly positively correlated.There was a significant positive correlation between astragaloside IV and HMGR expression.It was indicated that eight key enzyme genes played an important role in the synthesis and accumulation of astragalus saponin.3.Changes of soil nutrient contents under different water regulation modes and their relationship with the synthesis of astragalus saponinsThe total nitrogen and available phosphorus content in the water deficit group was lower than that in the water-rich group under long-term water control.The content of available potassium increased gradually,and the content of organic matter decreased gradually.There was a significant negative correlation between organic matter content and HMGS expression under short-term water regulation.There was a very significant positive correlation between soil available phosphorus content and HMGR expression.There was a significant positive correlation between soil available phosphorus content and astragaloside IV accumulation content expression.There was a significant positive correlation between alkaline nitrogen content and CAS expression under long-term water regulation.There is a very significant positive correlation between total nitrogen content and seven key enzyme genes other than HMGR.There was a significant negative correlation between available phosphorus content and AACT expression.There was a significant negative correlation between alkali nitrogen content and total saponin accumulation content.There was two very significant positive correlation between available potassium content and astragaloside IV accumulation content and available potassium content and total saponin accumulation content.It indicated that water regulation changed the soil nutrient content,which in turn affected the absorption and utilization of nutrients by A.membranaceus.The expression of key enzymes in saponin synthesis in A.membranaceus was rapidly responding to changes in the external environment,and finally show the difference in the content of astragalus saponins. |
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