Proline antioxidant role in the common ice plant subjected to salinity and paraquat treatment inducing oxidative stress |
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Authors: | N I Shevyakova E A Bakulina Vl V Kuznetsov |
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Institution: | 1.Timiryazev Institute of Plant Physiology,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | Leaves of 4-week-old (juvenile) and 9-week-old (adult) plants of the halophyte Mesembryanthemum crystallinum L. (the common ice plant), cultured under controlled conditions in the phytotron, were treated with paraquat (0.1 μM), which
produces superoxide radical, and (or) paraquat combined with introduction of NaCl (100 mM) or proline (5 mM) into nutrient
medium. After a 20-h dark period (23°C), plants were transferred into light (4 h at 54.1 W/m2 of photosynthetically active radiation) for stimulation of O°2− formation in plastids. Activities of antioxidant enzymes, the contents of MDA, H2O2, chlorophyll, and free proline were measured in leaves. Plant responses in two age groups, which differed in the type of
photosynthesis (juvenile plants had C3 type of photosynthesis, whereas adult plants were at the transition stage to Crassulacean Acid Metabolism (CAM) photosynthesis),
differed in the levels of constitutive proline and proline, induced by NaCl and paraquat, as well as in activities of superoxide
dismutase (SOD) and catalase. Changes in SOD activity and proline accumulation in response to paraquat treatment combined
with NaCl revealed opposite dependence to accumulation of proline: the more proline accumulated in leaves, the lower activity
of the enzyme. In response to paraquat treatment, the content of chlorophylls a and b most drastically declined in juvenile plants. Negative effect of salinity on the content of chlorophylls was lower than that
of paraquat and was almost the same in plants of both age groups. Protective effect of exogenous proline was most profound
in the case of paraquat treatment. Exogenous proline decreased the rate of lipid peroxidation, the content of superoxide radical
and, consequently, SOD activity (almost fivefold), and increased the content of chlorophylls (a and b) in leaves of adult plants. The obtained data suggest that stress-induced accumulation of proline in the common ice plant
has both osmoprotectory and antioxidant functions. |
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