The Effect Of Exogenous MeJA On Physiological Characteristics And TAs Metabolism Of Atropa Belladonna L. Under UV-B Stress

Atropa belladonna L.is the only medicinal plant source of tropane alkaloids?TAs?in China?authorized by pharmacopoeia of The People's Republic of China 2010?.The main medicinal components of Atropa belladonna L.are hyoscyamine and scopolamine which are important anticholinergic agents.They are widely used in clinical practice,and the market demand is huge.UV-B stress significantly affects plant growth and physiological metabolic processes,especially the synthesis of secondary metabolites.A large number of studies have shown that MeJA participates in the stress response of plants under stress and plays an important role in inducing the synthesis of secondary metabolites.In this study,we used Atropa belladonna L.seedlings as material.By spraying exogenous methyl jasmonate?MeJA?,and setting MeJA treatment groups with different concentration gradients:0?mol�L^-1,50?mol�L^-1,150?mol�L^-1,250?mol�L^-1,350?mol�L^-1.We mainly studied the effects of different concentrations of exogenous MeJA and different treatment time?4 d,8 d,12 d,16 d?on the photosynthetic characteristics,physiological index of adversity,nitrogen metabolism,TAs content and precursor substances,synthetase activity,signaling molecule and key enzyme genes expression in TAs metabolic pathway of Atropa belladonna L.seedling under 10?W�cm^-2 UV-B stress,and initially explicated the regulation mechanism of physiological characteristics and TAs metabolism under UV-B stress.The main results are as follows:1.The photosynthetic characteristics and physiological index of adversity of Atropa belladonna L.after applying different concentrations of MeJA under UV-B stress.Under the UV-B treatment,the photosynthetic characteristics were significantly inhibited,proline content was reduced,and the membrane lipid peroxidation was aggravated;After treatment with MeJA,Fv/Fm,qP,ETR,Yield,photosynthetic pigment content,proline content and antioxidant enzymes?SOD,POD,CAT?activities were all enhanced,and F₀,NPQ,MDA content were all reduced.It indicates that MeJA is beneficial to alleviate the harm caused by UV-B stress in Atropa belladonna L.,improve photosynthesis,enhance the activity of antioxidant enzymes,reduce the degree of membrane lipid peroxidation,and improve resistance of Atropa belladonna L.to UV-B stress.2.The variation of the Nitrogen metabolism of Atropa belladonna L.after applying different concentrations of MeJA under UV-B stress.With the extension of UV-B stress time,the nitrate nitrogen content was significantly reduced,the ammonium nitrogen content was accumulated in large amounts,the free amino acid content and soluble protein content also continued to decrease,and the activity of the key enzyme in nitrogen metabolism of GDH first increased,and then decreased,the GS activity and NR activity continued to decrease,it indicates that UV-B stress caused disturbance of nitrogen metabolism of Atropa belladonna L..Under different MeJA treatment,250?mol�L^-1 MeJA was effective in increasing the content of nitrate nitrogen,free amino acids,soluble proteinon,and reducing the content of ammonium nitrogen.At the same time,250?mol�L^-1 MeJA was good on the key enzymes of nitrogen metabolism?NR,GS,GDH?.It indicates that the appropriate concentration of MeJA can availably promote the nitrogen metabolism of Atropa belladonna L.under UV-B stress,and provide sufficient precursors for TAs synthesis.3.The TAs content of Atropa belladonna L.after applying different concentrations of MeJA under UV-B stress.The hyoscyamine content showed a trend of increasing first and then decreasing with the extension of UV-B stress treatment days,while scopolamine content continued to decrease.After treatment with MeJA,the content of hyoscyamine and scopolamine both improved,and the effect was the most significant when the concentration of MeJA was 250?mol�L^-1.At the same time,the increase in scopolamine content was greater than that of hyoscyamine.This shows that the appropriate concentration of MeJA can efficaciously relieve the TAs accumulation in Atropa belladonna L.by UV-B stress,promote the conversion of hyoscyamine to scopolamine and increase the TAs content.4.In order to clarify the mechanism of MeJA regulating TAs synthesis of Atropa belladonna L.under UV-B stress,the polyamines?Put,Spd,Spm?,ODC activity,ADC activity,signal molecule NO and the relative expression of PMT,TR?,PPAR,H6H were tested.UV-B stress significantly reduced Put content and Spd content,inhibited ODC and ADC activity,and reduced NO content.Although the expression level of key enzyme gene TR?was slightly up-regulated under UV-B stress,but the expression of PMT and H6H was significantly suppressed.After treatment with 250?mol�L^-1 MeJA,polyamines content,?Spm+Spd?/Put value,ODC activity,ADC activity and NO content all increased in varying degrees.Meanwhile,250?mol�L^-1 MeJA treatment stimulated the efficient expression of TR I,PPAR and H6H.It is speculated that the regulation of TAs synthesis by MeJA mainly through affecting the metabolism of polyamines,increasing the Put content,the participation of the signal molecule NO,and at the same time increasing the relative expression of key enzyme genes to promote the synthesis of hyoscyamine and scopolamine.In summary,the appropriate concentration of Me JA is beneficial to alleviate the inhibition of UV-B stress on the photosynthesis,nitrogen metabolism and TAs accumulation in Atropa belladonna L..At the same time,it is conducive to reduce the degree of membrane lipid peroxidation.The regulation of TAs metabolism by MeJA plays a role by changing polyamine metabolism and the expression of key enzyme genes in TAs synthesis pathway.