Document Type : Original Article
Authors
Department of Biology, Faculty of Basic Sciences, Lorestan University, Khorramabad, Iran
Abstract
Introduction: Salinity is one of the most significant abiotic stresses that affects the metabolism of plant cells and reduces their productivity. High levels of salinity trigger ionic imbalance and osmotic stress in plants, which has severe effects on the morphology, biomass and biochemical processes of plants and ultimately leads to plant damage. Red bean with the scientific name Phaseolus vulgaris L. belongs to the family of legumes (Fabaceae) can be grown annually in temperate climates or perennially in tropical climates. It has been proven by various studies that up to 20% of bean production in the Middle East is wasted due to salinity. The most sensitive stage of bean plant to salt stress is during seed germination and the beginning of seedling growth. Regarding the high level of bean cultivation in Iran and the high sensitivity of this plant to salinity, identification of bean varieties resistant and sensitive to salinity helps to solve the cultivation of this plant in saline areas. Therefore, in this study, in order to identify red bean cultivars tolerant to salt stress, the effect of different levels of salt stress (concentrations of 50, 100 and 200 mM NaCl) on physiological and biochemical characteristics in the roots and leaves of two cultivars of red beans (Ofogh and Ks31285) was investigated.
Material and Methods: This research was conducted on two bean cultivars (Ofogh and Ks31285) obtained from Khomein Agricultural Research Center. The present study was conducted in the biology laboratory of Lorestan University in the year 1400. The bean seeds (Ks31285 and Ofogh) were surface sterilized (5.5% sodium hypochlorite for 10 minutes) for rapid germination and planted in 1.5 Liter pots containing perlite for two weeks in the cultivation room. The pots (two plants in each pot) were watered for about a week, and after a week until the fourteenth day, semi-Hoogland nutrient solution was added to the plant culture medium every other day. Salinity stress was applied at three levels of 50, 100 and 200 mM. After the end of this time period, morphological, biochemical and physiological indicators such as growth parameters (plant height, fresh and dry weight of aerial and terrestrial organs), the amount of chlorophylls and carotenoids, hydrogen peroxide (H2O2), lipid peroxidation (MDA), some osmolytes (reduced and soluble carbohydrates, proline) and the content and ratio of Na+ and K+ were measured. SPSS version 16 statistical software was employed to analyze data. Duncan's test (P ≤ 0.05) was used to compare the mean results of different treatments, and graphs were drawn using Excel software.
Results and discussion: The results showed that leaf RWC and growth indices decreased in both cultivars, but the amount of decrease in cultivar Ks31285 was higher than that of Ofogh cultivar, which indicates the high salinity tolerance of the cultivar. In addition, the results indicate that total sugar, reducing sugar and proline have increased in both cultivars, but, the amount of proline in Ks31285 was higher than Ofogh. On the other hand, as the salinity level increased, the amount of photosynthetic pigments (chlorophyll a and carotenoids) decreased and the level of malondialdehyde and hydrogen peroxide increased. The amount of this change was higher in Ks31285 than in Ofogh. These results also showed that the Ofogh cultivar had lower sodium and higher potassium in its leaves than to which in Ks31285.
Conclusion: Based on the results of this research, the tolerance to salinity in the Ofogh cultivar compared to the Ks31285 cultivar is due to the lower concentration of Na+, the higher concentration of K+ in the leaves, the higher accumulation of reducing and total sugars and the decrease in the amount of MDA in the leaves and roots. The sum of these factors resulted in increased growth indices (plant height, fresh and dry weight of aerial and terrestrial organs) and RWC, in the Ofogh cultivar, when compared to Ks31285 at all salinity levels. Despite the higher salinity tolerance of the Ofogh cultivar, the concentration of proline in it was lower than that of the sensitive Ks31285 cultivar.
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