Glycinebetaine accumulation, physiological characterizations and growth efficiency in salt-tolerant and salt-sensitive lines of indica rice (Oryza sativa L. Ssp indica) in response to salt stress

The aim of this research was to investigate betaine aldehyde dehydrogenase (BADH) and glycinebetaine (Glybet) biosynthesis in photoautotrophic rice seedlings. The role of Glybet on physiological and growth responses to salt stress in both salt-tolerant and salt-sensitive lines is to be investigated. The BADH activity in salt-tolerant seedlings cultured under extreme salt stress (342 mM NaCl) progressively increased during the first few hours until it peaked after 72 h. This was about 2.5 times greater than in salt-sensitive plants. Similarly, the amount of Glybet detected in salt-tolerant lines was 1.3 times more than in salt-sensitive lines at 96 h salt exposure. The BADH activities were positively related to Glybet accumulation in both salt-tolerant and salt-sensitive lines. The accumulation of Glybet in salt-tolerant lines was directly correlated with pigment stabilization. Relative water content in the salt-tolerant lines was closely related to water oxidation in photosystem II (PSII), defined by maximum quantum yield of PSII (F-v/F-m). In addition, a high concentration of total chlorophyll is more efficient in capturing light energy, defined by photochemical quenching. The concentrations of chlorophyll a and total carotenoid were positively related to the quantum efficiency of PSII (Phi(PSII)) and non-photochemical quenching, respectively, resulting in a high net-photosynthetic rate (NPR) and the promotion of growth. The high level of Glybet in salt-tolerant lines plays a role as a salt defensive response mechanism in terms of pigment stabilization and water oxidation in PSII, resulting in high NPR and growth efficiency.