| Panax notoginseng (Bruk) F.H.Chen, commonly known as notoginseng, is a perennial herb that belongs to the Araliaceae family of the genus Panax. It is used to promote blood circulation, counteract blood stasis, relieve swelling and pain, and treat cardiovascular and cerebrovascular diseases. P. notoginseng is the largest ingredient in traditional Chinese medicines. Yunnan Province, the herb’s primary producing area, provides more than 95% of the total radix notoginseng on the Chinese market. Yunnan is located on a large plateau with a monsoon climate. Yunnan has suffered five successive years of drought, with the situation worsening year by year. P. notoginseng grows under cool conditions, and its growth has been seriously affected by drought in Yunnan. In 2014, the drought area included more than 80% of the total planting area of P. notoginseng, and irrigation accounted for 10% of the total planting cost. Irrigation-related spending tends to increase as drought conditions intensify. Currently, P. notoginseng cultivation suffers from a lack of scientific guidance, and irrigation factors such as time, methods, and water use largely depend on experiences. This lack of data increases costs and creates a significant waste of water resources. Even worse, it leads to waterlogging and affects the normal growth of P. notoginseng. Reasonable, scientifically-based irrigation represents a promising strategy to save cost, improve efficiency, and enhance yields. Therefore, it is important to establish irrigation rules for P. notoginseng cultivation. In this study, we demonstrate the effects of different SWCs on the growth, development, physiological and gene expression characteristics of 2-year-old flowering stage P. notoginseng.The main results of this study are as follows:1. Effect of different water conditions on the physiological indexes (e.g. seed water content, vigour, antioxidase activities) of Panax notoginseng seeds were studied under process of after-ripening and germination. Results show that compared with 2.5% treatment, under the treatment of of 5%, P. notoginseng seeds possessed stable seed water content, the seed vigor was exceed by 51%, variation of antioxidant enzyme (SOD, POD, CAT) activity and malondialdehyde (MDA) content were small, crude fat and total sugar content decreased significantly. With the increase of PEG 6000 concentration, the germination characteristic indexes obviously decreased, antioxidase activities increased first and decreased afterwards, content of MDA, soluble protein and total sugar increased obviously. There were significant positive correlation between germination characteristic indexes and osmotic substance content (R>0.900, P<0.01), and significant negative correlation with MDA (R>0.900, P<0.0l). In conclusion, because the characteristic of dehydration intolerance of P. notoginseng seeds,5% water content of sand burying stratification treatment was the best for after-ripening,15% concentration of PEG 6000 treatment was the highest tolerance limit of germination process.2. It is a study that the effects on physiology of Panax notoginseng seedlings, including antioxidant enzymes, osmotic substances and root activities were detected under simulated drought stress by PEG 6000. The result showed that in roots and leaves the activities of POD and APX kept rising with increasing processing concentration and time. However, on the one hand, in the same processing time, in roots and leaves SOD firstly increased and then decreased with the increasing of processing concentration. On the other hand, in the same processing concentration, SOD activity kept rising with the extension of processing time. In addition, in roots and leaves the activity of CAT tended to increase with the increasing of concentration in the same processing time, while it increased at first and then decreased with the extension of time in the same concentration. In stem, the activity of SOD and APX did not change obviously, whereas CAT activity in stem increased with the increasing of processing time and concentration. With the increasing of processing concentration and the extension of processing time, the MDA, soluble protein, proline content and root activity in leaves and roots apparently were rising. Moreover, fluorescence signal of H2O2 and NO in root tip enhanced as the processing concentration increased after treated for 1 d. In summary, P. notoginseng seedlings could against drought stress by the system of antioxidant enzyme, permeating stress substances and impeded stress signal substances. Thus, when the concentration of PEG 6000 was more than 5%, it would have harm on P. notoginseng seedlings.3. This study investigated the effects of different soil water conditions (SWCs) on the growth, development and saponin content of 2-year-old flowering stage Panax notoginseng. Plants were grown for 30 days in soil with different water contents of 25%(treatment group T2),40% (T3), and 55%(T4). Compared to the plants grown under T3 condition, T2 and T4 condition plants demonstrated reductions in flower growth; T2 induced the initiation of fibrous root, while T4 induced the decrease of fibrous root that caused by root rot disease. Exposure to extreme SWCs (T2 and T4) also resulted in decreased dry matter accumulation and growth in all plant organs except the stem, as well as reductions to relative water contents, chlorophyll contents, and photosynthetic efficiency. Contents of soluble total sugars and proteins increased significantly in all the parts but flowers under extreme SWCs (T2 and T4). Most notably, extremely high or low SWCs (T2 and T4) could improve the accumulation of total saponin. However, the underground parts (root tuber and rhizome) of P. notoginseng were less sensitive to changes in SWC, the aboveground organs were more sensitive. Furthermore, extremely high or low SWCs decreased the main monomer saponin concentrations in P. notoginseng roots. Low SWC enhanced main monomer saponin accumulation in stem and leaf, while high SWC improved accumulation in flower. The expression of key genes of saponin synthesis pathway increased under T2 and T4 treatment than T3. These results suggest that 40% SWC for flowering stage P. notoginseng produced the best agronomic traits, while extreme SWC produce more saponin contents by improving the expression of key genes in saponin synthesis pathway.4. The effect of Panax notoginseng of three years simulated drought stress by PEG 6000 on antioxidant enzyme system in leaves, the content of ginsenoside, expression of key genes in saponin biosynthesis of leaves were studied. The result indicated that, in addition to the control, at the same time with the increase of PEG concentration and under the same PEG concentration as time increases POD, SOD, CAT and APX activity was first increased and then decreased in the leaf of Panax notoginseng. In the 2.5% PEG 6000, the activity of antioxidant enzymes showed maximum. Therefore, the results showed that with the increasing of treatment time in 2.5% PEG 6000 the number of differential expression genes in the metabolic pathways of terpenoids and ketones Increased firstly and then decreased. It had largest quantity of differential expression genes in the metabolic pathways of terpenoids and ketones at 12 h. And the determination of the content of saponin and expression of genes in saponin biosynthesis in leaves under 2.5% PEG 6000 treatment, the content of Rb1、Rb2 and Rb3 were the highest in the leaf of Panax notoginseng after treatment 12 h with 2.5% PEG 6000, and after treatment 36 h, the content of Rc was the highest. After treatment 24 h, the content of Rb1 was lowest. After treatment 3 h, the content of Rb2、Rc and Rb3 were the lowest. And After treatment 12 h, Rb1+Rc+Rb2+Rb3 sum of the maximum,3 h minimum. The relative expression of ACAT, HMCAS, PMK and DS were first increased and then decreased with the increase of the treatment time. The relative expression of GGPS, SE and IPI were first decreased and then increased and then decreased trend with the increase of the treatment time. The relative expression of MDD, HMCAR and MVK did not change significantly. In the all, here was the impact of the synthesis and content of saponin of Panax notoginseng in leaves with 2.5% PEG 6000 treatment under a short time, the 2.5% treatment 12 h, the antioxidant enzyme activity and monomer saponin content is the biggest. |
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