Effects Of Selenium On The Physiological Response Of Panax Notoginseng

Selenium?Se?is an essential trace element for the human body,and which is conducive to the growth and development,quality improvement of the plant.However,the current research that the application of selenium on plants mainly focuses on the food and cash crops,a little reports on medicinal plants,especially in panax notoginseng,which is one of the first batch of Chinese herbal medicines that have passed the national GAP certification.Which affect the two-way regulatory function of hemostasis and activation.Yunnan province is the mainly planting areas of panax notoginseng.While the soil selenium in the panax notoginseng cultination areas was lower than the average value in China?0.29 mg/kg?.The Se in plants were mainly obtained from soil,the Se content of panax notoginseng would be lower when the soil selenium content were inadequate in the panax notoginseng cultination areas in Yunnan province,and affected the growth and efficacy of medicinal components of panax notoginseng strongly.Therefore,we researched the physiological response mechanisms of panax notoginseng on selenium via field investigations,hydroponic and pot experiments,the related laws of absorption and translocation in selenium were revealed,and the effects of selenium on the content of dencichine and saponins of panax notoginseng was explored.The major conclusions from this research are following:1.To measure the selenium and dencichine in plant and soil in panax notoginseng and planting soil in 18 cultination areas in Yunnan province,and it was made clear that selenium is directly related to the synthesis of dencichine.To study the effects of physiology and the dencichine content in two-year-old panax notoginseng through sodium selenate and sodium selenite?0-30?M?in hydroponic experiments,which was aimed to determinate the effects and mechanisms of the anti-stress and dencichine content under Se treatments,and ascertained the valence of Se that is more suitable for growth and development of panax notoginseng.The results shown that the Se in plant and soil were 0.21-1.18 mg/kg and 0.16-0.32 mg/kg in 18planting areas in Yunnan province respectively,and the dencichine content of roots were 0.69%-0.98%.The relationship between the dencichine and Se content in soil or plants showed strong positive correlation?R²=0.19**,R²=0.31***,p<0.01?.The Se treatment with low concentrations??2?M?significantly increased the antioxidant capacity,enhanced the NO and H₂O₂ contents of anti-stress signal substance,reduced the malondialdehyde?MDA?content of panax notoginseng.and the treatments with selenite and selenate promoted the content of dencichine by 157.58%-165.04%and156.51%-181.61%in hydroponic experiments,respectively.However,the Se treatment with high concentration?10?M?resulted in the excessive production of reactive oxygen species?ROS?produced,and the dencichine content decreased.The contents of ASA treated with 2?M selenite was significantly higher than that of CK,while there were no significant differences in ASA content under each concentration of sodium selenate treatment in hydroponic experiments.The Se content in roots were higher than that in shoots under the treatment of selenite,then the results were opposite when applied with selenate.In summary,soil Se may be an important mineral element in the biosynthesis of dencichine,and which could improve the antioxidant capacity and dencichine content with appropriate supplementation.The antioxidant capabilities under selenite treatment were better than that of selenate,the former was more beneficial for the accumulation of selenium in panax notoginseng roots.2.The pot experiments were conducted to research the effects of agronomic traits and photosynthetic characteristics,the change laws of antioxidant system and the contents of saponins and dencichine of two-year-old and three-year-old panax notoginseng at different concentrations of sodium selenite?0-10 mg/kg?with foliar spraying.The results showed that the application of 5 mg/kg selenite not only promoted the growth of leaf width,leaf length,petiole length,plant height and stem diameter by increasing the SPAD values in leaf,photosynthetic parameters?P_n,C_i,T_r?and chlorophyll fluorescence parametere Fv/Fm,reduced stomatal conductance G_s,resulting in increased the biomass;but alao enhanced the activities of SOD,POD and CAT,increased GSH and ASA contents,decreased the content of MDA caused by peroxidation of panax notoginseng.The content of Se and dencichine in panax notoginseng roots were raised as the selenite treatment concentration increasing.The saponins content were significantly increased under 5 mg/kg Se treatment,while the saponins content were decreased and the leaves turn to yellow in a part of two-year-old panax notoginseng with treatment concentration was raised?10 mg/kg?.By comparison,the highest saponins content appeared with the 1 mg/kg treatment,and leaves changed yellow when the treatment concentrations exceeded 5 mg/kg of three-year-old panax notoginseng.In conclusion,the Se treatments under low concentrations promoted the growth and photosynthesis,increased the yield,and enhanced the antioxidant effect of panax notoginseng.The high concentrations of Se treatments were made for the Se content and dencichine accumulation in roots,but there were adverse effects on the previous indicators.There were differences in agronomic traits and saponin contents on the selenite concentration response of two-year-old and three-year-old panax notoginseng.Therefore,appropriate selenium supplementation with foliar spraying was beneficial for the growth and development of panax notoginseng,and the accumulation of dencichine.3.Effects of dencichine?0-50?M?on the regulation of root activity,antioxidant system and ROS content in panax notoginseng were carried out by hydroponic experiments.This study designed to determine whether dencichine plays a role in any anti-stress mechanisms.The results showed that the dencichine treatment?30?M?significantly enhanced the root activity,increased the antioxidant capacity,enhanced the non-enzymatic contents,decreased the ROS content,and reduced the lipid peroxidation of the cell membrane.While high concentration dencichine treatment played stress effects on physiological,which induced the increase of ROS content,decreased the activity of roots,and reduced the antioxidant effect in panax notoginseng.Above all,dencichine involved in the regulation of anti-oxidative enzyme activity,enhanced the anti-oxidant ability,reduced the lipid peroxidation of the cell membrane,kept the low level of active oxygen in panax notoginseng,and prevented them from excessive free radical poisoning.4.Effects of interaction between Se?2?M sodium selenite?and Sulfur?S??0-4mM MgSO₄·7H₂O?on the antioxidant system,the change of dencichine and saponins contents,and the key enzyme gene expression levels in dencichine synthesis of panax notoginseng were studied by hydroponic experiments.The purposes of this study were to clarify the regulatory mechanism of the anti-oxidation system under Se-S interaction,and reveal the effect of the dencichine synthesis of panax notoginseng with sulfur on selenium.The results showed that Se and S treatments alone enhanced antioxidant enzyme activities and increased non-enzymatic contents,so as to eliminate ROS and reduce MDA content.Se alleviated the damage of ROS caused by high concentration S treatments.Meanwhile,S inhibited the accumulation of Se,and increased the content of saponins in shoots of panax notoginseng.In addition to Se content under Se₂,Se₂S₂ and Se₂S₄ treatments of panax notoginseng,the Se content at each trertments were lower than that of CK.The interaction between selenium and sulfur promoted the accumulation of dencichine,but the response of concentrations were different,the highest content of dencichine was under the Se₂ treatment,while the content of dencichine under sulfur treatments were higher than that of CK,but which were lower than the corresponding Se-S treatment.The key genes in the dencichine biosynthesis pathway of?-cyanoalanine synthase?CAS?and serine acetyltransferase?SAT?were significantly upregulated,and the gene of cysteine synthase?CS?was downregulated by the treatment of Se-S interactions,the results were consistent with the dencichine content.In summary,the effects of enhancing the anti-oxidation capacity,promoting the up-regulation of CAS and SAT genes,and the down-regulation of CS gene to increase dencichine content under the treatment with Se₂.The results were better than the treatments of sulfur and the interaction between selenium and sulphur.It showed that selenium can enhance the sulfur in panax notoginseng to exert antioxidation and increase dencichine content.Therefore,it was recommended that selenium fertilizer should be used instead of sulphur fertilizer according to actual needs for further development.