Response Of Isodon Rubescens (Hemsl.) Hara To Pb Stress And Its Regulation

In recent years, excessive heavy metal (especially Pb) occurs in the production process of medicinal plant Rubescens [Isodon rubescens (Hemsl.) Hara], affecting the quality of medicine safety as well as exports of the products. The study covered the tests of Pb stress on I. rubescens, spot sampling and testing I. rubescens which grown in different introduced areas and different classes of origin, and regulation technologies screening and verification, explored the influences of Pb on the propagation, physiology, and growth of I, rubescens and its mechanism, as well as the main factors in I. rubescens that absorb, transfer, and accumulate heavy metal Pb, and regulating technical approach; thus, The main results are as follows:1. Impacts of Pb stress on seed germination: At lower Pb concentration (135 mg/L), seed germination of Rubescens was not significant to the control; relatively high concentrations of Pb stress (270 mg/L,540 mg/L,1080 mg/L) on seed germination and embryo growth had significant inhibiting effects (P<0.05); radicle is a more sensitive part to Pb Stress (P<0.05); Pb coefficient of Rubescens seed germination was 0.76～2.59; Pb enrichment in embryo is the main reason for the inhibition to growth. Through the predictive analysis of the fitting model, Pb critical concentrations were 195.18 mg /L and 101.65 mg/L, which reduced the germination rate and biomass fresh weight ratios by 10%.2. Impacts of Pb stress on physiological aspects: There were uncertain effects with concussion on chlorophyll and carotenoid synthesis in different period under Pb stress. Low-mid Pb concentrations can promote chlorophyll synthesis, and the bioaccumulation of high Pb concentration can inhibit the chlorophyll synthesis and restrict the growth of Rubescense at the time of 50 d. The activity of superoxide dismutase (SOD), Peroxidase (POD) and Catalase (CAT) were different between the leaves and the roots under Pb stress. Leaves prevent the oxidative stress by the activities of POD and CAT synergistic effect, while root mainly prevent oxidative stress by SOD; Pb tolerance critical value in Rubescens was 826.08 mg/ kg.3. Impacts of Pb stress on the growth and secondary metabolites: No significant effects on the growth of Isodon rubescens at low and mid level of Pb concentrations (135 mg/L,270 mg/L) were found, but under high Pb concentration (540 mg/L), the biomass and relative growth rate decreased by 33.33% and 46.59% respectively compared with the control group. Based on the fitting model’s predictive analysis, the critical Pb concentration was 301.99 mg/L,which lowered the relative growth rate(RGR) by 10% to the control group (P<0.01). The contents of the active component Oridonin was increased with the improvement at Pb concentrations (135 mg/L～540 mg/L).4. The analysis for sampling from different site types of Rubescens growing in the wild and introdution area showed: Pb contamination in soil, the distance to Pb pollution source, and pH of rain(acid rain) were the main factors that caused Pb bioconcentration in Rubescens; the order of Pb contents in different organs in a decreasing:leaf> flower> root> stem> seeds, Pb contents differed significantly at different harvest time, among which the highest was in November. Pb absorbed and transferred in Rubescens mainly from soil and air, which largely accumulated in leaves. Under soil cultivation, Pb accumulation coefficient and transfer coefficient in Rubescens was 0.06～0.23 and 0.65-1.79.5. The screening tests for Pb regulation technologies showed:Se fertilizer, BIOCHAR, EM fertilizer, Ca, Zn had significant anti-Pb effects, among which the effects of Se fertilizer and BIOCHAR were more remarkable. BIOCHAR and BIOCHAR base fertilizer with Se foliar fertilizer increased the biomass by 12.0% to 12.1%, but no significant effect on Oridonin content. Pb dissolution rate in water decoction and ethanol extract of I, rubescens was 1.23% ～ 1.49%, the 2 processes effectively reduced Pb contents in the refined products made from I. rubescens.6. Initially identified the main cultivation technologies for lower Pb content in I. rubescens:Pb content in planting soil should be limited within 55.82 mg / kg, lead pollution source above 4 km, more than 200 m away from road, air quality 1～2 grade; fertilization: base fertilizer to the application of Biochar, Se foliar fertilizer was better; best harvest time should be in May and June.The technologies could effectively reduce Pb content in I. Rubescens and its products which can fit for green standard for medicinal plant export (China) or EU standard, improve the biomass and ensure the quality, and provided the scientific basis for the safety and the quality.