The effect of salinity stress on the amount of proline, chlorophyll and sodium and potassium ions in different rice cultivars in hydroponic environment

Introduction Among the cereals, rice is the most important human food source after wheat and has a major place in human nutrition in terms of production and cultivation. This plant is susceptible to salt stress and its response to salt stress varies with growth stages, concentration and duration of impact. Materials and methods This study was carried out in factorial experiment in a completely randomized design with three replications in the research greenhouse of Sari University of Agricultural Sciences and Natural Resources in 1977-98. The first factor was 71 rice genotypes and the second factor was salinity stress with 4 levels. The germinated seeds were transferred to hydroponic medium to prepare the culture medium from Yoshida nutrient solution (Yoshida et al., 1994). Chlorophyll extraction of rice leaf by Arnon method (1997), Proline amino acid extraction from leaf tissue by Bets et al. (1973) and for determination of sodium and potassium ions from leaf by Hamada and Elnai method (1994) used. The data obtained from these traits were analyzed by SAS and SPSS statistical software and compared by means of Duncan's multiple range test and clustering of genotypes by cluster analysis of tolerant cultivars based on this. Attributes were identified. Results and discussion Results of analysis of variance for different physiological traits under salinity stress showed that genotype, salinity and their interaction effects were statistically significant at the 5% probability level for all measured traits. Comparison of mean salinity levels in all measured traits was significant at 5% probability level. It showed that proline amino acid content and leaf tissue sodium content increased with increasing salinity and zero (normal) level with minimum and salinity level 9 The highest Ds was obtained and the chlorophyll pigment and potassium content of leaf tissue decreased with increasing salinity level and the highest (zero) level and the lowest salinity level was 9 dS / m. Within plant cells, proline acts as an osmotic preserving agent between the cytoplasm and the cell vacuole, and proline protects the plant against free radical damage. In the present experiment, proline content increased significantly with increasing salinity dose. This increase was higher in tolerant cultivars than in susceptible cultivars. An important effect of increasing salinity is leaf senescence and the main factor causing leaf senescence is the decrease in chlorophyll content under salinity stress. In this study, total chlorophyll a, chlorophyll a and chlorophyll b also decreased significantly under salinity stress, which was in line with the results of Bori Boncast et al. (2013) and (Wijita et al., 2018). Higher concentrations of potassium ions in the leaves of tolerant cultivars exposed to salinity can be a adaptive response to high potassium ion storage in stomach cells in salinity stress (Fallah 2015). Aerial is one of the mechanisms of plant tolerance against salinity stress. The results of this study are in line with the results of Hong et al. (2012).Conclusions The results of this study showed that salinity stress significantly decreased chlorophyll pigment and leaf potassium ion content and significantly increased proline amino acid and sodium ion content of leaf. Mean comparison between cultivars under salinity stress showed that Shastak Mohammadi, Nemat, Tarom Ghali, GASMAL, Neda, Roshan, NONABOKRA, FL478, Dilmani and Barley at 9 dS m-1 were the most tolerant cultivars to salinity and salinity stress. Saleh, Rashti Cold, IRBLZFU, IR39595, IR29, Black tip and Dorfak at 9 dSm-1 were the most susceptible cultivars to salinity stress. Acknowledgements Thanks to Sari University of Agriculture and Natural Resources and the Genetics and Plant Breeding Laboratory for providing some of the cost of this research as well as for providing plant specimens.