Salinity Effects on Na⁺, K⁺, ABA and IAA Concentration and Distribution in Two Contrasting Rice (Oryza sativa) Genotypes During Seedling Stage

Soil salinity affects plant growth and development and is a major concern for crops productivity worldwide. Rice (Oryza sativa), a salt-sensitive species, particularly during the seedling stage and has considerable genetic variation for salt tolerance within the cultivated gene pool. This study, was conducted to determine the effects of salinity on [Na⁺], [K⁺], [ABA], [IAA] and their distributions in plant tissues during seedling stage. Two rice genotypes differing in their tolerance to salinity were evaluated in a greenhouse experiments under salt stress during seedling stage. In salt-sensitive cultivar Na⁺ accumulated in all leaves and [K⁺] had not changed, while in tolerant cultivar Na⁺ and K⁺ concentrated in oldest leaves. Results showed that [ABA] in sensitive genotype was much higher than tolerant genotype whilst, [IAA] was higher in tolerant genotype. At the beginning of salinity stress, IAA in root and leaf sheaths of both genotypes had no significant change, while after extension of salinity stress, distribution of [IAA] in tolerant cultivar gradually changed from roots and leaf sheaths to leaves, especially older leaves. Such distribution was not observed in sensitive genotype. These results show that differences in the level of osmotica and saline stress are related to their different capacity of phytohormones synthesis and transport.