Common and distinctive responses of rice seedlings to saline- and osmotically-generated stress

Drought and salinity are the major abiotic factors limiting productivity in rice (Oryza sativa L.). Although both generate osmotic stress, ion toxicity is an additional and important component of salinity. To study the morphological and anatomical responses to those types of stress, we used in vitro grown rice seedlings. Based on an initial screening of several non-penetrating osmotica on seedling growth, we selected sorbitol to compare its osmotic effects during seedling development with those generated by NaCl stress. At comparable levels of osmolality, the reduction in root and leaf growth as well as their delayed development were similar for both saline- and osmotically-generated stress. Some changes observed in root anatomy and most of the variations in leaf anatomy features caused by the treatments could be ascribed to osmotic stress. However, there were evident differences in the morphology of the root system as well as in chlorophyll levels as a function of the stress treatment. Furthermore, the larger size of epidermal and bulliform cells was distinctively related to saline stress. The results obtained provide tools for the in vitro identification of either specific or cross-tolerant phenotypes.