| Panax notoginseng (Burk.) F.H. Chen is a perennial herb having been used in traditional Chinese medicine. The herb has various pharmacological actions and is traditionally used for the treatment of cardiovascular diseases, inflammation, trauma, and hemorrhage. Because of the arsenic pollution in P. notogiseng plantation area, the growth of plant and the accumulation of medical active ingredient are injured seriously, and it has posed a major risk to human health and international trade. The purpose of this study was to reveal the mechanism of arsenic transport, transformation, and tolerance in P. notogiseng, and thereby provide some data reference for the control of arsenic pollution in the plant. In this study, we investigated the influence of soil As concentration on the growth and As accumulation of pot-cultured P. notoginseng. The objectives were to characterize the existence of As in P. notoginseng, e.g. chemical forms of As and their distributions at sub-cellular levels, and understand the mechanisms of As-tolerance under As-stress conditions. The main results were as follows:The biomasses presented an order of root>leave>stem in both of the treatment. The root, stem, and leaves in the high-As soil grew considerably more slowly compared with those growing in the low-As soil, with the percentage decreased by57%,41%, and40%, although neither showed obvious symptoms of As toxicity.In the low-As, the MDA content are very close in different part of plant, and presented an order of leaves>root>stem. In the high-As, it presented root>leaves>stem, with the percentage increased50%,14%, and17%respectively, but only the root increased statistically significant. It means arsenic could lead to membrane lipid peroxidation mardly in P. notogiseng, especially root.Flavone mainly accumulated in leaves. In high-As, the flavone content of root, stem, and leaves decreased26%,0.58%, and23%respectively. Saponin mainly accumulated in root. In high-As, the saponin content of root, stem, and leaves decreased17%,2.9%, and13%respectively.Arsenic mainly combined with crystalline hydrous oxides of Fe and Al(F3, F4), and the percentage was69%in high-As, but37%in low-As. The percentage of non-specifically sorbed arsenic (F1) was only0.50-0.55%in the two kinds of soil, and thereby decreased the toxicity of arsenic in p. notogiseng. The percentage of specifically-sorbed arsenic (F2) was about28-32%, which showed higher arsenic activation risk.In low-As treatment, the mean arsenic concentration was the highest in leaves (1.93mg/kg). While in high-As, the mean arsenic concentration increased significantly, with the highest in root (20mg/kg). Both of the BCFs were much less than1, and decreased as the arsenic concentration increased. It means the accumulation ability is poor in p. notogiseng. The TF was1.68in low-As, but0.35in high-As. It means the transport ability is strong in P. notogiseng, but arsenic stress will inhibit this mechanism.Arsenic mainly exists as As(Ⅴ) in both of soils. It could only be detected As(Ⅲ) indifferent part of P. notogiseng in low-As treatment, but both of As(Ⅲ) and As(Ⅴ) could be detected in high-As,, The mean concentration of As(Ⅲ) in root, stem, leaves were2.35,1.74,0.84mg/kg, and the mean concentration of As(Ⅴ) were1.30,0.86,0.77mg/kg. In addition, althouth the concentration of As(Ⅲ) was significantly higher than As(Ⅴ) in root, the two speciations have no significant difference in the xylem sap. It means that the transport ability through xylem for As(Ⅴ) may be better than As(Ⅲ).In high-As and low-As treatment, there were53%and54%of arsenic accumulated in cell wall,39%and39%of arsenic in cytoplasmic supernatant,8%and7%of arsenic in cell organelle. It means cell wall and cytoplasmic supernatant play key roles in the accumulation and detoxification of arsenic in P. notoginseng and the store ability in different subcellular fractions would not be affected by arsenic concentration.Compared with plants growing in the low-As soil, those growing in the high-As soil had a65%,1184%, and54%higher SOD activity in their roots, stems, and leaves respectively; all increases were statistically significant (all P<0.05). Similarly, the POD activities was increased in plants growing in the high-As soil by150%,277%and11%in their roots, stems, and leaves, with the former two being statistically significant (both P<0.05). In contrast to SOD and POD, the CAT activities was reduced by23%in roots,25%in stems, and11%in leaves compared with the counterpart activities in tissues derived from the low-As soil; but all of them were not statistically significant (P<0.05). The GSH activities was decreased in plants growing in the high-As soil by54%,32%,21%in their roots, stems, and leaves; all decrease were statistically significant (P<0.05)... |
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