Research On The Mechanism Of Salicylic Acid Regulates The Aluminum Resistance In Panax Notoginseng

Panax notoginseng(Bruk)F.H.Chen is a perennial herb that belongs to the Araliaceae family of the genus Panax and has good curative effects on many diseases.P.notoginseng is the main raw material of Chinese patent medicines,and the annual demand for proprietary Chinese medicines and decoction pieces is approximately 20,000 tons.The P.notoginseng cultivation soils in Yunnan province are mainly acidic red soil with low average p H.The planting of P.notoginseng will further accelerate soil acidification.The bauxite mineral resources are abundant in Yunnan province,and their distribution is highly coincident with the P.notoginseng cultivation area.With the further intensification of soil acidification,the bound aluminium in the soil dissolves into active aluminium,which produces a toxic effect on the plant.Al toxicity is one of the limiting factors for the growth of crops in acid soil.In order to solve the aluminum toxicity and increase crop yield in acid soil,it is very important to study the toxicity of aluminum on crops and the aluminum tolerance mechanism of crops.In this study,the P.notoginseng seedlings were used as experimental materials.The alleviating mechanism of salicylic acid was studied in P.notoginseng aluminum stress.The main research results are as follows:1.The physiological response of P.notoginseng to Al stressThe survey results show that the average total Al content in soil is 119.2 g·kg-1,active Al is 3.30 g·kg-1,and active Al account for 2.8% of the total Al content.The plant-soil Al content of P.notoginseng is higher than the cultivation soil of other crops in Yunnan province.The average soil p H is 5.38.The average Al content and enrichment coefficient in P.notoginseng are in the following decreasing order: rootlet > rhizome > main root > stem and leaf.There is a significant positive correlation between the content of soil active Al or total Al and the Al content of various organs in P.notoginseng.Under the treatment of 400 ?M Al,the relative root elongation rate of P.notoginseng is reduced by 45.45%,the biomass is reduced by 16.48%.Compared with other plants,P.notoginseng has high Al tolerance.Al stress inhibits the root activity of P.notoginseng.However,the content of O2-·,MDA and H2O2 is increased significantly under Al stress and result in loss of plasma membrane integrity.Under low aluminum stress,the activities of antioxidant enzymes in plants increase.When the Al concentration exceded 400 ?M,the activities of some antioxidant enzymes(SOD,POD,APX)decrease to a maximum,indicating that the protective enzyme system was not sufficient to resist aluminum stress.This causes damage to the cells and is not conducive to the growth of P.notoginseng.Al treatments also reduce the content of chlorophyll,thereby reducing the net photosynthetic rate,which also indicate the toxic effects of Al on the growth of P.notoginseng.2.Distribution characteristics of Al in P.notoginseng The distribution of Al in the organs of P.notoginseng was in the following decreasing order: rootlet > rhizome > main root > leaf > stem,results show that Al is mainly enrich in the underground parts of P.notoginseng.The respective decreasing order for the cells is: cell wall > organelle > cytoplasm.Al accumulation percentage in cell wall of P.notoginseng exceeds 60%.The share/percentage of Al content in cytoplasmic supernatant was less than 13%.Al treatments significantly increase the content of pectin and increase the expression of Pn PME3,Pn PME7 and Pn PME40.The results show that the pectin component in the cell wall is the main binding site of Al in various parts of P.notoginseng.3.Effect of salicylic acid(SA)on Al-induced oxidative damage in P.notoginsengAl stress significantly induce the increase of activity of phenylalanine ammonia-lyase(PAL)and benzoic acid 2-hydroxylase(BA2H)in P.notoginseng roots,which promote the increase of endogenous salicylic acid content in P.notoginseng.However,abscisic acid(ABA)and auxin(IAA)content are almost unaffected by Al stress.The application of exogenous SA reduce the production rate of superoxide anion(O2-·),hydrogen peroxide(H2O2)and malondialdehyde(MDA)content,increase the chlorophyll content of P.notoginseng and fresh-dried biomass,and promote the growth of P.notoginseng;PAC inhibits the alleviating effect of SA on P.notoginseng Al toxicity.The application of exogenous SA increase the activity of superoxide dismutase(SOD),peroxidase(POD),and ascorbate peroxidase(APX)in roots of P.notoginseng compare with Al stress alone,while catalase(CAT))activity is reduced.These results suggest that P.notoginseng is dependent on PAL and BA2 H enzymatic pathways to increase the content of endogenous SA under Al stress,and SA further reduces the aluminum-induced oxidative damage and alleviates the toxic effects of Al on plants by regulating intracellular H2O2 levels.4.The role of SA signal transduction pathway in P.notoginseng under Al stressThe NO content was significantly up-regulated by SA,while it was down-regulated by PAC.SNP and c PTIO treatment had no significant effect on the SA content of P.notoginseng.Both SA and SNP could reduce the activity of PME,inhibit the expression of Pn PMEs,and increase PMD under Al stress,which was accompanied by a significant decrease of pectin and Al contents.SA synthesis inhibitor PAC,and the NO inhibitor c PTIO can play a negative regulatory role.These results indicate that based on the NO signaling pathway,the SA signal deceased the PMD of P.notoginseng under Al stress.This results in the decrease of the binding capacity of P.notoginseng cell wall pectin to Al and ultimately reduces the root Al content.Thus,under the Al stress,NO may act downstream of SA signaling and regulate P.notoginseng seedlings root cell wall pectin PMD under Al stress.