Study On Allelopathy Of Alkaloids In Sophora Alopecuroides L. From Xinjiang

Sophora alopecuroides L.is a perennial herbaceous shrub belonging to the genus Sophora of the family Leguminosae,which mainly distributes in Northwest China.In this study,S.alopecuroides growing in suburban of Changji,Xinjiang,was chosen as the research object.Through petri dish bioassay,the plant toxicity activities of aqueous extract and ethanol extract of roots,stems,leaves,flowers and fruits of S.alopecuroides were analyzed.Total alkaloids in S.alopecuroides fruits were extracted by solvent extraction combined with ultrasound,and their allelopathic effects were investigated.The allelopathic effects of 6 alkaloids with strong biological activity on 2 dicotyledons and 2 monocotyledons were tested by petri dish test and greenhouse pot experiment.Finally,changes of the phytohormone and antioxidant system in the recipient plant seedlings were analyzed.Our results indicate:（1）The aqueous extract(50 mg·mL^-1)of S.alopecuroides flowers had the strongest allelopathic effect,and completely suppressed the growth of root length and shoot length of four plants（Amaranthus retroflexus,Medicago sativa,Lolium perenne and Setaria viridis）.The effect of S.alopecuroides leaves was weaker than flowers,which completely inhibited the growth of root length of the four plants,and the growth inhibition rate on shoot length of receiver plants was 91.26-100%.The allelopathic effect of the aqueous extract of S.alopecuroides stems was medium,and the growth inhibition rate on root length and shoot length of receiver plants were 99.85%-100%and 92.31%-98.76%,respectively.The average inhibition rates of the aqueous extract of S.alopecuroides fruits and roots on root length of tested plants were 64.60%and 59.59%,respectively.But the average inhibition rate of the fruits and roots extracts of S.alopecuroides on shoot length of the four tested plants was less than 10%.（2）The allelopathic effect of the ethanol extract from the leaves of S.alopecuroides was the strongest,with an average IC₅₀ value of 5.92 mg·mL^-1 on the total length of the four tested plants.The average IC₅₀ value of the ethanol extract from S.alopecuroides fruits was 6.20mg·mL^-1 on the total length of four tested plants.The average IC₅₀ of the ethanol extract from stems,flowers and roots of S.alopecuroides on the total length of four tested plants was 15.32mg·mL^-1,15.54 mg·mL^-1 and 15.81 mg·mL^-1,respectively,showed the weaker allelopathic effects.（3）The results of petri dish bioassay showed that the alkaloids in S.alopecuroides had obvious phytotoxic activity against the recipient plants,and the effect intensity was greatly different.The inhibitory effects of 6 alkaloids and their mixture on root length of receiver plants were in the following order:sophocarpine>aloperine>mixture>sophoridine>matrine>oxysophocarpine>oxymatrine,with the corresponding IC₅₀ values being 0.565,0.718,1.069,1.146,1.436,2.168,and 2.340 mg·mL^-1,respectively.Greenhouse pot experiment showed that alkaloids showed relatively weak allelopathy.The inhibitory effect of alkaloids in S.alopecuroides on the root length of receiver plants was ranked as follows:matrine>mixture>sophocarpine>oxymatrine>oxysophocarpine>sophoridine>aloperine,and the corresponding IC₅₀ values being 4.626,4.987,6.524,7.476,8.347,15.104 and 15.921 mg·mL^-1.In conclusion,sophocarpine and mixture has stronger allelopathic inhibition in petri dish test and greenhouse pot experiment than other monomer alkaloids.（4）Under different concentrations of mixture treatment,the changes of phytohormone content in M.sativa seedlings were significantly different.The content of indoleacetic acid（IAA）increased dose-dependent with the increase of mixture concentration.When the maximum concentration was 2500μg·mL^-1,the content of IAA increased by 1261.99%compared with the control.The content of cytokinin（CTK）decreased significantly with the increase of mixture concentration,ranging from 23.56%to 68.86%.In addition,the content of abscisic acid（ABA）decreased gradually with the increase of the mixture concentration,and when the concentration was 2500μg·mL^-1,the content of ABA was almost zero.（5）The content of malondialdehyde（MDA）and the activities of peroxidase（POD）,superoxide dismutase（SOD）and catalase（CAT）in M.sativa seedlings were dose-dependent under different concentrations of mixture treatment.The content of MDA and the activity of POD increased with the increase of mixture concentration.When the maximum concentration was 2500μg·mL^-1,the content of MDA and the activity of POD increased by 228.40%and 48.09%,respectively.The activities of SOD and CAT decreased with the increase of mixture concentration.When the concentration was 2500μg·mL^-1,the activities of SOD and CAT decreased by 56.13%and 48.36%,respectively.The above experiments indicated that S.alopecuroides possessed strong allelopathic effects,which affected root and shoot length,plant hormone and antioxidant system of recipient plants.This study is helpful in terms of understanding the chemical and ecological mechanisms of S.alopecuroides malignant expansion and provides an important theoretical basis for the restoration of degraded grassland.