Study On The Effect Of Exogenous Ornithine And Nitric Oxide On The Alleviation Effect Of Potamogeton Crispus Under Cd Stress

Cadmium (Cd) is a strongly toxic heavy metal, which enters the aquatic ecosystems mainly through mining, metallurgy and chemical industry, and can be easily taken up by aquatic plants, leading to a variety of toxic effects to them, and is transferred to humans through the food chain, so it is necessary to effectively control Cd pollution in the aquatic ecosystems.Recently, some research at home and abroad show that ornithine (L-Orn) and nitric oxide (NO) can relieve toxicity effects to plants induced by stresses, suggesting that they also may alleviate Cd toxicity to plants to a certain extent. So in this study, steriles of widespread submerged plants Potamogeton crispus L. cultured by tissue culture technology, were used as experimental materials, and40μmol/L Cd were selected as the stress factors, and the effects of the supplementation of exogenous L-Orn and NO to Cd-treatment on relief to Cd toxicity were investigated to explore the exogenous L-Orn and exogenous NO relief physiological and biochemical mechanisms in order to provide theoretical reference for Cd pollution in the aquatic ecosystems. The results are as follows:1. The effects of2mmol/L exogenous ornithione (L-Orn) application on Cd accumulation, superoxide anion (O2-) generation rate, photosynthetic pigments, hydrogen peroxide (H2O2), malondialdehyde (MDA) and soluble protein contents, as well as the metabolisms of proline and polyamines under40μmol/L Cd stress were investigated. Results indicated that (1) Cd addition alone promoted a substantial accumulation of Cd to335.00μg/g FW and apparently induced oxidative stress, specific performance as follows:obviously raised O2-generation rate, H2O2and MDA contents, as well as decreased photosynthetic pigments and soluble protein contents. Meanwhile, exogenous application of L-Orn markedly inhibited the accumulation of Cd to232.50μg/g FW, reduced ROS level, alleviated membrane lipid peroxidation and retarded the degradation of photosynthetic pigments and soluble protein.(2) Single Cd treatment slightly increased proline content to1.91-fold than control by activating pyrroline-5-carboxylate (P5CS) activity and restraining proline dehydrogenase (PDH) activity, whereas exogenous addition of L-Orn further activated P5CS and ornithine-δ-aminotransterase (OAT) activities, thus significantly increasing proline accumulation to8.36-fold than control.(3) Cd exposure alone enhanced arginine decarboxylase (ADC), diamine oxidase (DAO) and polyamine oxidase (PAO) activities, as a result, increasing putrescine (Put) content and reducing spermidine (Spd) and spermine (Spm) contents. However, adjunction of exogenous L-Orn sharply added Put content by strengthening ADC and ODC activities compared with single Cd treatment, and encouraged Put to transform into Spd and Spm, moreover reduced PAO activity, hence raised Spd and Spm contents, finally increased total polyamines content. The results demonstrated that the supplement of exogenous L-Orn restrained ROS accumulation, membrane lipid peroxidation and the degradation of photosynthetic pigments and soluble protein thought inhibiting the accumulation of Cd and involving in regulation of proline and polyamines metabolisms, consequently to a certain extent enhanced Cd stress tolerance of P. crispus.2. The effects of supplement of exogenous SNP (0.1μmol/L、1μmol/L、10μmol/L and100μmol/L) on antioxidant system of P. crispus were studied. The resulted showed that40μmol/L Cd stress alone markedly increased O2-generation rate, H2O2and MDA contents as well as decreased soluble protein content. However, supplement of low dosage of SNP can reversed above changes induced by Cd, showing that NO can alleviate Cd-induced oxidative stress. On the other hand, Cd stress raised SOD^POD and CAT activities and reduced APX activity and AsA and GSH contents, indicating that Cd stress breaked metabolic balance of antioxidant system, however, exogenous NO can reversed the changes above because NO can directly scavenged ROS to regulate the antioxidant system of P. crispus.3. In this study, we investigated effects of NO supplementation as SNP on photosynthetic pigments content and polyamine and proline metabolisms in P. crispus under40μmol/L Cd stress. Cd exposure significantly reduced photosynthetic pigments content. However, supplementation of low dosage of SNP (0.1μmol/L、1μmol/L、10μmol/L) significantly revered Cd-induced degradation of photosynthetic pigments, suggesting that NO had protective effects on alleviating Cd toxicity. Further analysis demonstrated that there were significant increases in contents of Put and proline and the activities of ADC, ODC, PAO and P5CS as well as significant decreases in contents of Spd and Spm and the activities of DAO, OAT and PDH under Cd stress alone. In contrast, the application of low dosage of SNP (0.1μmol/L、1μmol/L、10μmol/L) together with Cd significantly increased the contents of Spd, Spm and proline and the activities of ADC, DAO, P5CS and OAT along with decreased Put content and the activities of ODC, PAO, and PDH. However, upon supply of the high dosage of SNP (100μmol/L), there were no obvious effects on polyamine and proline metabolisms. Therefore, effects of NO on polyamine and proline metabolisms were responsible for alleviating Cd-induced oxidative stress in P. crispus. Furthermore, all concentration of SNP promoted Cd accumulation in P. crispus, suggesting that NO contributed to Cd accumulation.