Reseach On Allelopathy And Antioxidant Activity Of Astragalus Strictus

Astragalus strictus is a perennial herb, which belongs to the Astragalus of leguminosae,is mainly distributed in Tibet, some parts of Qinghai and Sichuan Province. A. strictus is akind of poisonous plant and swainsonine is its main toxic components. A. strictus and somepoisonous plant of Oxytropis are collectively called locoweed and cause severe poisoningwhen eaten by livestock. At the same time, A. strictus grows so fast that the structure ofgrassland vegetation was deteriorated. The study on toxic ingredients of A. strictus andpoisonous weed control can reduce the harm to animal husbandry and grassland ecology,which is the most direct path and has attracted much attention. However, little research hasbeen done on the development and utilization of A. strictus, and so far no allelopathy andpolysaccharide antioxidant research has been published.Using the overground part of A. strictus as donor material in this research, which isdistributed on Gongbujiangda County, Tibet autonomous region. The acceptor plants wereAvena sativa, Amaranthus retroflexus, Trifolium repens and Capsella bursa-pastoris. Theaqueous extract from A. strictus was extracted by ultrasonic extraction with water and itsconcentration was classified into five classes:0mg/mL,12.5mg/mL,25mg/mL,50mg/mLand100mg/mL. Seed germination, root length, seeding height and fresh weight of fourreceptor plants, malondialdehyde （MDA） content, the activities of superoxide dismutase（SOD）, peroxidase （POD） of A. sativa and T. repens were researched to reveal the allelopathiceffect of A. strictus by using petri dish filter paper method.Applied orthogonal design （L16（44×23）） and ultrasonic assisted extraction to optimize thesix factors that effect polysaccharide extraction process, including sonication time, sonicationtemperature, solvent-to-solid ratio, sonication power, sonication repetitions and solution pH.Orthogonal design with three factors and three levels, alcohol precipitation method was usedto research separation technology of A. strictus polysaccharide. And the three factors wereethanol concentration, ethanol precipitation time and the amount of ethanol added. Measuringhydroxyl radical scavenging capacity and reducing power of polysaccharide that was extracted and separated from A. strictus, in order to study the antioxidant capacity of A.strictus polysaccharide.The research contents and results were listed as follows:1. Allelopathy of aqueous extracts from A. strictusThe aqueous extract from A. strictus inhibited the germination and seedling growth ofA. sativa, and the inhibition was enhanced with extract concentration increasing. Thegermination of A. retroflexus, T. repens and C. bursa-pastoris were inhibited by the aqueousextracts of A. strictus, their seedling growth presented the concentration effect of promoting atthe low concentration and inhibition at the high concentration. A. retroflexus seeds wereinhibited completely so that they could not germinate when A. strictus concentration was100mg/mL.The activities of SOD, POD and MDA content of A. sativa and T. repens were affectedby different concentrations of aqueous extract. SOD, POD activities and MDA contentmarkedly increased at50mg/mL （P<0.05）, whereas at100mg/mL the extract increased thecontent of MDA and reduced the enzymatic activity in the seedling of A. sativa and T. repens.Therefore, A. strictus shows great allelopathic potential.2. The antioxidant activity of A. strictus polysaccharidesThe optimal extraction method of A. strictus polysaccharides was conducted for10minutes at pH=9, and at a temperature of80°C, the ratio of solid to liquid was1:25, theultrasonic power was350W and extraction was performed twice. The best isolation techniqueconsisted of a3-hour precipitation using five volumes of absolute ethyl alcohol. The hydroxylfree radical scavenging capacity and reducing power of the A. strictus polysaccharides werepositively correlated with the concentration of A. strictus polysaccharides in the range of0.2-1.0mg/mL, and the IC₅₀for hydroxyl radical was2.75mg/mL. The polysaccharides hadsome antioxidant activity, providing a theoretical basis for the further development of theutilization of A. strictus.