Morpho-Physiological and Stress-Related Gene Expression of Rice Varieties in Response to Salinity Stress at Early Vegetative Stage

This study focuses on the growth and morpho-physiological responses of the Malaysian commercial variety MR219 rice to salinity stress during the early vegetative stages, specifically during germination and the five-leaf stage. For germination responses, MR219 seeds were grown for 10 days in different salt concentrations. Low salinity significantly improves seed germination and increases the total number of germinated seeds. However, higher salinity (160 mM NaCl) inhibits the germination of MR219 seeds and reduces the total number of germinated seeds by 93.3%. The effects of salinity on the five-leaf stage of MR219 were also determined and compared to the salinity-tolerant (Pokkali) and susceptible (IR64) varieties. There were significant reductions in the photosynthesis rate, transpiration rate, stomatal conductance, and leaf chlorophyll content by 28.1%, 58.6%, 81.1%, and 3.7%, respectively. These reductions could contribute to the significant decrease in growth parameters measured throughout the treatment period. Based on the principal component analysis (PCA) result, MR219 is more tolerant to salinity than IR64, but is less tolerant than Pokkali. Further investigation on stress-related gene expression suggests that significant changes in the transcript level of genes involved in gamma-aminobutyric acid (GABA) shunt, ion transport, and reactive oxygen species detoxification could be attributed to the adaptation and tolerance level of each variety to salinity stress.