Does exogenous glycinebetaine affect antioxidative system of rice seedlings under NaCl treatment?

The effect of exogenously applied glycinebetaine (GB) on the alleviation of damaging effects of NaCl treatment was studied in view of relative water content (RWC), malondialdehyde content, and the activity of some antioxidant enzymes in two rice (Oryza sativa L.) cultivars differing in salt tolerance (salt-tolerant Pokkali and -sensitive IR-28), comparatively. Both cultivars took up exogenously applied GB through their roots and accumulated it to considerable levels. Leaf RWC of both cultivars under salt treatment showed an increase with GB application. The activities of superoxide dismutase (SOD), ascorbate peroxidase (AP), catalase (CAT), and glutathione reductase (GR) increased in leaves of Pokkali, but peroxidase (POX) activity decreased under salinity. In IR-28, the activities of SOD, AP and POX increased, whereas CAT and GR decreased upon exposure to salt treatment. When compared to the salt-treated group alone, GB application decreased the activities of SOD, AP, CAT, and GR in Pokkali, whereas it increased the activities of CAT and AP in IR-28 under salinity. However, the activity of POX in IR-28 under salinity showed a decrease with GB application compared to the NaCl group. In addition, lipid peroxidation levels of both cvs. under salt treatment showed a decrease with GB treatment. Therefore, we conclude that GB protects both rice seedlings from salinity-induced oxidative stress.