| Sterile seedlings of Potamogeton crispus L. were cultured by tissue culture technique, and were used as experimental materials. In this study, the effects of exogenous calcium (Ca) application on mercury (Hg) accumulation, mineral nutrition, photosynthetic pigments, superoxide anion (O2-), hydrogen peroxide (H2O2), malondialdehyde (MDA), vitamin C and E, glutathione (GSH) and polyamines metabolism of the tested plants under the stress of1.5μM Hg2+stress were investigated. The results demonstrated that,(1) Hg2+stress induced a substantial accumulation of Hg2+at165.79μg/g FW and resulted in serious imbalance of nutrient elements, such as inhibiting the absorption of P, K, Fe, Mg and Na, whereas exogenous Ca2+significantly reduced the accumulation of Hg2+by66.4%and effectively reduced the Hg-induced imbalance of nutrient elements in Potamogeton crispus L..(2) Hg2+treatment severely reduced chlorophyll concentration, chlorophyll a/b ratio, and raised O2-generation rate, H2O2and MDA contents, while increased the levels of Vc, VE and GSH. Application of exogenous Ca2+markedly retarded the degradation of photosynthetic pigments and also significantly improved the levels of antioxidant capacity in the tested plants.(3) Hg2+treatment enhanced polyamine oxidase (PAO), diamine oxidase (DAO), and arginine decarboxylase (ADC) activities, moreover reduced ornithine decarboxylase (ODC) result in decrease of putrescine (Put) and spermine (Spm) and slightly increase of spermidine(Spd) content. Exogenous Ca2+altered polyamines content of Hg2+stress by modulating polyamines metabolizing enzymes activities, mainly presented as significant increase in Put and Spm contents, and further increased the ratio of free(Spd+Spm)/Put. These results indicated that the supplement of exogenous Ca2+relieved the phytotoxicity of Hg2+to Potamogeton Crispus L. by depressing the accumulation of Hg2+and involving in regulation of a series of physiological and biochemical mechanisms, particularly polyamines metabolism. In another study, the effects of exogenous calcium (Ca) application on antioxidase system, soluble protein, antioxidant capacity (T-AOC), non-protein thiols (NP-SH), phytochelatins (PCs) and proline metabolism of the tested plants leaves under Hg2+stress were investigated. The results demonstrated that,(1) Single Hg2+stress resulted in serious imbalance of antioxidase system, such as restrained the activities of catalase (CAT), ascorbate peroxidase (APX), and glutathion reductase (GR), while no outstanding changes were observed in superoxide dismutase(SOD) and peroxides (POD). Meanwhile,25mmol·L-1exogenous application of Ca markedly retarded the degradation of antioxidases and effectively enhanced SOD, POD, APX and GR activities in Potamogeton crispus L.(2) Hg2+treatment severely reduced soluble protein content and T-AOC, as well as promoted a substantial accumulation of NP-SH and PCs. Application of exogenous Ca2+apparently reversed this situation and decreased the levels of NP-SH and PCs.(3) Proline is a kind of important osmolyte in aquatic plants on exposure against abiotic stresses. Adjunction of exogenous Ca2+increased proline accumulation significantly by activating pyrroline-5-carboxylate (P5CS) and rnithine-δ-aminotransferase(OAT) activities. Our results demonstrated that Hg2+disturbed the intrinsic balance of antioxidant defense system in the tested plants, and the supplement of exogenous Ca2+relieved the phytotoxicity of Hg2+to Potamogeton Crispus L. by promoting the synthesis of soluble protein, increasing the activities of antioxidant enzymes and the contents of antioxidant substances, maintaining high total antioxidant capacity and involving in regulation of a series of physiological and biochemical mechanisms, particularly proline metabolism. |
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