Study Of Exogenous Ca²⁺ On Physiological Characteristics And Secondary Metabolites Accumulation Of Atropa Belladonna L. Seedling Under UV-B Stress

Ultraviolet B（UV-B）radiation does harm to growth and development of plants.Ca²⁺is one of the most necessary elements for plant growth and development.Ca²⁺is not only a major necessary element which is needed for the growth and development of plants but also a second messenger which involved in responding to outside environment,and it plays an important role in regulating plant stress signal transduction.Research shows,exogenous Ca²⁺can enhance the ability of plant to resist stress and regulate the synthesis of secondary metabolites.In order to clarify the effects of exogenous Ca²⁺on physiological characteristics and regulate secondary metabolites of Atropa belladonna L.seedlings under UV-B stress,we used Atropa belladonna L.seedlings as material.Changeless strength of UV-B radiation and different concentration of Ca²⁺were set which included:0 mmol·L^-1,2 mmol·L^-1,4mmol·L^-1,6 mmol·L^-1,8 mmol·L^-1.The effects of to investigate photosynthetic characteristics,physiological index of adversity,nitrogen metabolism,secondary metabolite content and key enzyme genes espression of tropane alkaloids metabolic pathways in response to different concentration of Ca²⁺and treatment durations under UV-B Stress.The main conclusions are as follows:1.With the increase of the number of radiant days,UV-B radiation have caused the inhibition of photosynthetic characteristics,and aggravated peroxidation of membrane lipid;The F₀,MDA content gradually decrease,but the Fv/Fm,qP,ETR,photosynthetic pigment content and antioxidant enzyme activity gradually increasing under Ca²⁺treatment.This shows Ca²⁺is propitious to relieve inhibitory effect on photosynthesis and enhance resistance under UV-B stress.2.Investigating the variation of the nitrogen metabolism under UV-B stress,we found GDH activities and soluble protein content first increase and then decrease,but nitrate nitrogen content,free amino acid content,NR activities and GS activities had been steadily dropping with the increase of the number of radiant days.This shows UV-B radiation make against nitrogen metabolism.Under different concentrations Ca²⁺treatment,nitrate nitrogen content reduced,but free amino acid content,soluble protein content,NR activities,GS activities and GDH activities become raise in different levels.This shows appropriate Ca²⁺can effectively promote nitrogen metabolism process.3.Investigating the effect of alkaloid content and relative expression levels of key enzyme coding genes of tropane alkaloids metabolic pathways under UV-B stress,we found hyoscyamine content first rise and then reduce,and scopolamine content have been steadily dropping.Then,the content of hyoscyamine and scopolamine become raise in different levels under Ca²⁺treatment.In order to explore its mechanism,using real-time fluorescence quantitative PCR,we found UV-B radiation can lead to increased expression of TR I gene,but produce inhibition of the expression of pmt and h6h genes.Then,the relative expression levels of PMT,TRΙand H6H become raise in different levels under Ca²⁺treatment.In summary,UV-B radiation make against photosynthesis,nitrogen metabolism and accumulation of alkaloids.And UV-B radiation can aggravate peroxidation of membrane lipid.Appropriate exogenous Ca²⁺can relieve inhibitory effect on photosynthesis,promote nitrogen metabolism and be propitious to accumulate tropane alkaloids under UV-B stress.This research could provide a theoretical references for plantation in field.