| P. ginseng and P. quinquefolium, all belonging to Araliaceae family, are widely cultivated in China, and used in traditional herbal medicine. However, they cannot be planted consecutively on the same land otherwise their yield and quality will be greatly reduced. The obstacle of re-plantation has been considered to be caused by the soil sickness, pathogenic fungal accumulation, allellopathy and autotoxicity. Ginsenoside is the major pharmaceutically-active component in ginseng and American ginseng, which can be found in their root exudates and old ginseng soils. However, the allelopathic activity of ginsenoside and its monomers and their influences on the recipient plant are less studied. Our studies aim:(i) to detect ginsenoside content in the ginseng of different growth-year and in different collection time and plot via HPLC method;(ii) to understand the allelopathic effects of the total ginsenoside (TGS) and its monomer fractions Rb1, Re and Rg1on ginseng seedling growth and development at different concentration(25mg·L-1,50mg·L-1and100mg·L-1);(iii) to examine the reaction of American ginsengs treated with ginsenoside of different concentration, extracted from4-year American ginseng with water;(iv) to study the influence of ginsenoside on the roots and adventitious roots of four cultivars-cabbage, cucumber, wheat, and mung bean;(v) to test the allelopathic effects of ginsenoside on ginseng seedling growth when they were planted in natural soils mixed with0.125g·kg-1,0.25g·kg-1and0.5g·kg-1TGS. The key conclusions are showed as below:1. The TGS content of different growth-year ginsengs and ginsengs in different collection time and plot is distinctively different. The TGS contents extracted from the dried soils increased constantly as growth year prolonged. In both understory and farmland ginseng soils, the TGS content in June were higher than that in August. On the contrary, the TGS content in American ginseng soils in August were higher than that in June, and TGS content increased with growth year increasing. Rb1, Rb2, Rb3, Re, Rd and Rg1were detected in the ginseng soils of3-5year-old. The TGS content in the dried ginseng soils was approximately from0.031to0.332mg·g-1(average:0.0795mg·g-1); the TGS content in American ginseng soils was from0.025to0.154mg·g-1(average:0.0732mg·g-1), whereas the TGS contents in farmland soil were0.002-0.076mg·g-1(average:0.0213mg·g-1).2. The four compounds all affected the root vigor (RV) and root length (RL) of ginseng seedling in different ways. The TGS and the Rb1treatments both showed a dose-dependent effect on RV; The RV enhanced drastically as the TGS and Rb1concentration increased, and then when their concentration moved to some certain level which is relatively high the RV began to decline. When the Rgl concentration was low, the RV was inhibited. And as the Rgl concentration went up, the RV increased as well. But just like the TGS and the Rbl, the RV then turned down quickly. As Re concentration increased, the RV enhanced slowly but constantly. For those ginsengs that were treated with ginsenoside at lower concentration (25mg·L-1), the chlorophyll synthesis was promoted. The promotion effect of the four compounds was in order:TGS>Rg1>Re>Rb1, and even if the promoting effect grew weaker as concentration increased, the chlorophyll content was still higher than that of the control. Electron microscope showed that the plasma membranes were detached from the cell wall, the structures of mitochondria and vacuolus were also dissolved under higher TGS and Rbl concentration. Hence, these abnormal physiological parameters in plant growth process indicated the responsibility of ginsenoside concentration.3. The ginsenoside extracted from American ginseng with the deionzed water showed a dose-dependent effect on the root elongation. However there was no significant difference between the biomass of seedlings and roots before and after. The root vigor was inhibited significantly as Ginsenoside concentration increased. The production of O2-in seedlings sped up markedly as ginsenoside concentration increased and exposure time prolonged. The synthesis of soluble protein and chlorophyll in the seedlings was slightly stimulated by the ginsenoside. The promoting effect declined as the concentration increased and the treatment time prolonged, but the content is still higher than that of the control. Otherwise, the MDA content and the relative electric conductivity in leaves and roots increased slightly compared with the control as the concentration increased and the application time prolonged. The treated ultra-structure of root-tip cells showed that the nuclear membrane and nucleolus deformed and the vacuole membrane dissolved with the treatment time prolonging. The ginsenoside affected the underground growth of American ginseng more than aboveground growth. Taken together, these findings indicated that ginsenoside affected the early growth of American ginseng.4. The alleopathic effect of TGS on the root growth of four cultivar species was conspicuously different.The RV, RL and RFW (root fresh weight) of wheat, cabbage and cucumber declined constantly as ginsenoside concentration ascended. However, the ginsenoside treatment had almost no influence on the hypocotyl adventitious roots of cucumber and mung bean. The RL, RFW, RV and Root number of mung bean adventitious roots had no significant response to ginsenoside, although the antioxidant enzymes activity rose a little bit over the control. Thereby, ginsenoside inhibited the root growth of the four indicator plants, and had stronger inhibitory effects on wheat and cucumber than on cabbage. However, there was no evidence to indicate that ginsenoside affected the hypocotyl cuttings growth in cucumber and mung bean.5. The result of the experiment done with the soils from the new understory land indicated that there was no significant change in the biomass of the ginseng seedlings treated with ginsenoside, whereas the root elongation was reduced significantly by7.0%under higher concentration, the RV was declined by69.3%, and the fresh weight of roots slid by45.5%. The soluble protein content had little changes, yet the chlorophyll content had been in an uptrend. Even though the chlorophyll content decreased under higher concentration, it was still higher than that of the control. The color of ginseng roots changed to brown when TGS reached the highest. The IAA content first increased and then decreased as concentration ascended; the GA3content in all the treatments declined; the ABA content had no significant difference at lower concentration, but it increased sharply to2.39times than of the control when treated with high ginsenoside concentratrion.Hence, we concluded that triterpenoid ginsenoside and their three monomers all disturbed the growth and development of ginseng and American ginseng, and this disturbance was affected by the types and the concentrations of ginsenosides. The ginsenoside do had allelopathic effect on other plants, yet it was lower than that on ginsengs and American ginsengs. It was found that triterpenoid ginsenoside may participate in the regulation of the formation and stability of plant population. |
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