Exogenous glycinebetaine affects growth and proline accumulation and retards senescence in two rice cultivars under NaCl stress

The ability of exogenously applied glycinebetaine (GB) for the alleviation of growth inhibition and senescence resulting from NaCl stress was investigated in view of growth parameters, net PS-II efficiency, photosynthetic pigments, protein and proline contents in two rice (Oryza sativa L.) cultivars differing in salt tolerance (salt-tolerant Pokkali, and salt-sensitive IR-28). Shoot fresh weight (FW) of Pokkali and shoot and root dry weight of IR-28 showed a decrease under salinity but an increase with exogenous GB application. NaCl treatment caused no serious decrease in FV/FM ratio of Pokkali whereas FV/FM ratio of IR-28 showed a remarkable decline throughout the experiment. Exogenous GB application partially preserved net PS-II efficiency of IR-28 from salt-stress. While Chl-b and carotenoid contents of IR-28 decreased, photosynthetic pigment contents of Pokkali showed no notable change under salinity. GB treatment did not show protective effect on photosynthetic pigment contents of IR-28 decreased under-salinity. Proline content significantly increased in Pokkali and IR-28 under salt-stress with a higher rate of increase in the former. When compared to NaCl-exposed groups alone, GB treatment caused an increase and a decrease in the level of proline accumulation in Pokkali and IR-28, respectively. While protein content of Pokkali enhanced with salinity, GB pre-application decreased it to control levels. Protein content of IR-28 showed a decrease under salinity but an increase with GB application. Therefore, we conclude that GB can reduce the impact of salt-stress on growth and senescence, enhance the photosynthetic efficiency of PS-II and increase the protein content of rice seedlings.