The Regulatory Mechanism Of Nitrogen Deficiency On Starch Accumulation Of Panax Ginseng

At present,it has been reported that the root of garden-cultivated ginseng is thicker than that of mountain-cultivated ginseng which is caused by the accumulation of starch.This difference interferes with the beautiful form of garden-cultivated ginseng.And,the accumulation of starch would weaken the glucose metabolism and affect the biosynthesis of ginsenosides.Therefore,the synthesis and decomposition of starch affect the external morphology and internal quality of ginseng root.However,it was found that the lack of nitrogen could lead to starch accumulation in the model plants.Further,our previous results showed that the nitrogen content in soil of garden-cultivated ginseng was lower than that of mountain-cultivated ginseng.Therefore,the reason of the difference of starch accumulation between mountain-and garden-cultivated ginseng,especially the mechanism of nitrogen deficiency regulating starch accumulation in ginseng,need to be clarified.It will provide a theoretical basis for revealing the differences in the external morphology and internal quality of ginseng,and also lay an experimental foundation for scientific guidance of ginseng planting.In this study,the regulatory mechanism of nitrogen deficiency on starch accumulation of ginseng was studied at plant and cell levels,and the results were as follows:(1)There were obvious differences in the morphology of mountain-and garden-cultivated ginseng.The total biomass of garden-cultivated ginseng was higher than that of mountain-cultivated ginseng.The body shape of garden-cultivated ginseng was thicker,the head and fibrous root of garden-cultivated ginseng are shorter.(2)The nitrogen content in soil of garden-cultivated ginseng was compared with that of mountain-cultivated ginseng in different years.The results showed that the nitrogen content of garden-cultivated ginseng was lower than that of mountain-cultivated ginseng.(3)The results of plant level research found that the nitrogen content was low,the ratio of nitrogen absorption and utilization decreased by 0.31 times,and the protein content was low in garden-cultivated ginseng.It indicated that the nitrogen metabolism level of garden-cultivated ginseng was lower than that of mountain-cultivated ginseng.(4)The starch content of garden-cultivated ginseng was higher than that of mountain-cultivated ginseng in different years.SSS and AGPase were the starch synthetase related enzymes.Their activities were 1.95 and 1.33 times higher in garden-cultivated ginseng than that of mountain-cultivated ginseng,indicating that the starch accumulation in garden-cultivated ginseng was higher.(5)The content of ginsenoside and the SS activity in garden-cultivated ginseng were lower than that in mountain-cultivated ginseng.The results showed that the ginsenoside biosynthesis in garden-cultivated ginseng was lower than that in mountain-cultivated ginseng,which may be one of the reasons that the efficacy of garden-cultivated ginseng is lower than that of mountain-cultivated ginseng.(6)At the cell level,ginseng suspension cells were cultured with different concentrations of nitrogen.With the decrease of nitrogen concentration,the absorption and utilization of nitrogen were decreased,the ability of protein synthesis was decreased,and the activity of key enzymes of nitrogen metabolism such as NR,GS,GLDH were decreased.That indicated nitrogen concentration affected the nitrogen metabolism of ginseng cells.(7)The decrease of ginsenoside content showed a linear positive correlation with the decrease of nitrogen concentration.The activity of ginsenoside synthesis related enzymes HMGR,SS and SE were decreased,indicating that nitrogen deficiency inhibited the ginsenoside biosynthesis.(8)In the absence of nitrogen,the starch content accumulation in cells,the sugar content was decreases,the aerobic respiration rate of glycolysis was decreases,the activity of key enzymes PFK-6,SPS,EL,a-KA and MDH were decreased and the level of glucose metabolism was decreased.This indicated that the accumulation of starch caused by nitrogen deficiency reduced the intracellular sugar level;(9)With the increase of sucrose concentration in ginseng cells,the starch content did not be accumulated,but the content of ginsenoside and the activity of the key enzyme for ginsenoside synthesis were increased.It indicated that the concentration of intracellular sugar directly affected the content of ginsenosides.(10)The starch decomposition inhibitor MBOA(2 mM)was added into normal medium and cultured for 6 days.The activity of AMY was inhibited,starch content was accumulation,and the contents of sugar and ginsenosides in the cells were decreased.The results showed that starch accumulation reduced sugar levels to inhibit ginsenosides synthesis.(11)Adding 8 mM of AGPase inhibitor was added into to normal medium for cultured 6 days.AGPase enzyme activity was inhibited,starch decomposition was increased.The content of starch was decreased and the content of intracellular sugar and ginsenosides were increased.In summary,nitrogen deficiency promotes starch accumulation by regulating AGPase expression,thereby reducing glucose content to inhibit the ginsenosides synthesis.These results provide experimental data for the exploration of "excellent shape and quality" functional genes in ginseng.