Effects of exogenous ornithine on resistance of Potamogeton crispus L.to cadmium stress
Sterile of Potamogeton crispus L.cultured by tissue culture technology,were used as experimental materials.In this study,the effects of 2 mmol/L exogenous ornithine (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 under 40 μmol/L Cd stress were investigated.Results indicated that (1) Cd addition alone promoted a substantial accumulation of Cd to 335.00 μg/g and apparently induced oxidative stress,specific performance as follows:obviously raised O2·-generation rate,H2O2 and MDA contents,as well as decreased photosynthetic pigments and soluble protein contents.Meanwhile,exogenous application of L-Orn markedly inhibited the accumulation of Cd to 232.50 μg/g,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 to 1.91-fold than control by activating pyrroline-5-carboxylate (P5CS)activity and restraining proline dehydrogenase (ProDH) activity,whereas exogenous addition of L-Orn further activated P5 CS and ornithine-δ-aminotransterase (OAT) activities,thus significantly increasing proline accumulation to 8.36-fold than control.(3)Cd exposure alone enhanced arginine decarboxylase (ADC),ornithine decarboxylase (ODC) 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 Potamogeton crispus L..
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