Environmental and Experimental Botany 56 (2006) 72–79 Exogenous glycinebetaine affects growth and proline accumulation and retards senescence in two rice cultivars under NaCl stress Tijen Demiral, Ismail T¨ urkan ∗ Department of Biology, Science Faculty, Ege University, 35100 Bornova-Izmir, Turkey Received 9 August 2004; accepted 12 January 2005 Abstract 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 F V /F M ratio of Pokkali whereas F V /F M 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. © 2005 Elsevier B.V. All rights reserved. Keywords: Chlorophyll fluorescence; Glycinebetaine; Proline; Rice (Oryza sativa L.); Salt-stress; Senescence 1. Introduction High concentrations of salt resulting from natural pro- cesses or mismanagement in irrigated agriculture result in inhibition of plant growth and yield. Coping with salt-stress is a global issue especially in many arid or semi-arid regions to ensure agricultural survival and sustainable food produc- tion. Conventional plant breeding attempts have changed over to use of physiological selection criteria since they are time consuming and rely on present genetic variabil- ity (Heuer, 2003). Currently, production of osmoprotectant Abbreviations: BADH, betaine aldehyde dehydrogenase; GB, glycine- betaine; PVPP, polyvinylpolypyrrolidone; SDS, sodium dodecyl sulphate ∗ Corresponding author. Tel.: +90 232 388 4000x2443; fax: +90 232 388 1036. E-mail address: turkan@sci.ege.edu.tr (I. T¨ urkan). compounds such as glycinebetaine (GB) via genetic engi- neering in higher plants attracts more attention. Neverthe- less, physiological approaches that enlighten the functions of complex systems involved in stress tolerance needs further research. Plants facing adverse situations such as high salt con- centrations lower their osmotic potential by accumulating osmolytes that do not perturb enzyme functions so as to maintain continuous water absorption at the low soil water potential (Robinson and Jones, 1986). Accumulation of these compatible solutes (osmoprotectants) such as proline and glycinebetaine, allow turgor maintenance and/or stabiliza- tion of proteins and membranes against destabilizing effects of abiotic stresses including salinity, drought and temperature extremes, all of which cause cellular water depletion. There- fore, exogenous application of these compounds promises an alternative/additional way to genetic engineering to improve 0098-8472/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2005.01.005