Study On The Pathogenesis Of Red Skin Disorder Of Panax Ginseng

Ginseng(Panax ginseng C.A.Meyer)is one of the most valuable traditional Chinese medicine varieties,which ranks first in the word in terms of cultivation area and yield.However,red skin disorder(RSD)of ginseng is a common non-infectious disease in ginseng planting areas.Its symptoms are red-brown or orange-yellow lesions on the epidermis of ginseng root.Fibrous root is fracture,even the whole peridermal is cracked and decaied.The occurrence of RSD is accompanied by a significant decrease in the content of active components such as ginsenosides,amino acids and polysaccharides.RSD seriously affectes the quality grade of ginseng from both external form and internal quality.According to statistics,RSD have occurred in China,South Korea,Canada and other countries,the incidence of light disease area is about 20-30%,serious disease area as high as 80%.In addition,because there is no significantly change in the overground parts of the diseased ginseng,early detection is difficult,resulting in damage to the ginseng resource reserves and a significant decline in economic benefits.Therefore,it is very important to identify the pathogenesis of RSD ginseng and find out its pathogenic genes.In this study,the main causes of RSD ginseng were screened by analyzing the topographic factors and the physicochemical properties of the soil,the nitrogen absorption and assimilation,ginsenosides and phenolic acid synthesis of RSD ginseng were analyzed at both plant and cell levels to elucidate the RSD pathogenesis.The results are as follows:(1)Through the field investigation and analysis of the topographic factors and soil conditions of RSD ginseng,it was found that when the growth slope of RSD ginseng was less than 15°,excessive water was stored in the soil,resulting in soil acidification.Under these conditions,the occurrence rate of RSD was as high as 72.1±0.44%.(2)Through the analysis of the metal elements content in the soil between RSD ginseng and healthy ginseng,it was found that the content of aluminum and iron in the soil of RSD ginseng were increased by 2.93±0.59 and 2.10±0.64 times,and the content of aluminum and iron in the plants were increased by 1.14±0.99 and 1.08±0.83 times,respectively,and the content of aluminum was the most significant.Moreover,aluminum stress promoted the accumulation of aluminum and iron in ginseng cells due to metal interaction.More importantly,when the pH of culture medium decreased to 4,the absorption of aluminum by ginseng cells was promoted to 3.86±0.36 times.Therefore,RSD may be caused by soil acidification promoting aluminum stress.(3)By analyzing the content of metabolites(protein,NO3-and NH4+)and the activity of key enzymes(nitrate reductase(NR),glutamate dehydrogenase(GLDH),glutamine synthetase(GS)and glutamate synthase(GOGAT)in nitrogen absorption and assimilation in RSD ginseng and aluminium-stressed ginseng cells,RSD and aluminum stress could inhibit the absorption and utilization of nitrogen and lead to the disorder of nitrogen metabolism.(4)The contents of ginsenosides in RSD ginseng and aluminium-stressed ginseng cells were decreased by 35.71±0.56% and 21.49±0.92 times,respectively,and the activity of the key enzyme of ginsenoside synthesis,squalene synthase(SS),was decreased by 41.24±0.81% and 25.76±0.57 times.Moreover,nitrogen deficiency caused the decrease of ginsenoside content and SS activity under aluminium-stressed,indicating that the decrease in ginsenoside biosynthesis of RSD ginseng is due to nitrogen disturbance.(5)The content of phenolic acid in RSD ginseng and aluminium-stressed ginseng cells was increased by 24.53±0.58% and 27.67±0.68%,respectively.Their key enzyme activity of phenolic acid synthesis,phenylalanine ammonia-lyase(PAL),was increased by 50±0.94% and 53.45±0.46%,the activity of PPO was increased by 38.46±0.63% and 39.72±0.90%.These results indicated that the synthesis and oxidation of phenolic acid in RSD ginseng and aluminium-stressed ginseng cells were increased.However,the content of phenolic acid was decreased by 29.16±0.88%,the activity of PAL was decreased by 38.83±0.51%,and the activity of PPO was decreased by 38.67±0.43% with the decrease of nitrogen source.Under the same nitrogen source with aluminum stress,the content of phenolic acid was increased by 46.50±0.58%,PAL activity was increased by 47.47±0.48% and PPO activity was increased by 49.84±0.52%.The results showed that the accumulation of phenolic acid was directly induced by aluminum and did not depend on the absorption and assimilation of nitrogen.