Salt tolerance of sorghum varieties in terms of fresh weight, ion accumulations, proline content and peroxidase activity was analyzed in this study. Three sorghum varieties, Payam, Kimia, and Jambo, differing in salt tolerance, were grown in a greenhouse-hydroponic culture with a complete nutrition solution to which 0, 50, 100, 150 and 200 mM NaCl was added. Plant roots and leaves were harvested at 15 and 30 days after treatment and subjected to analysis. Clear decline in K ? and Ca 2? concentrations and increase in Na ? and proline contents were observed in the root and leaf tissues at each NaCl concentration in all varieties during the NaCl treatment. The Ca 2? concentration in leaves was higher than in roots, and had the following order in the tested cultivars: Jambo, Kimia, and Payam. Total peroxidase activity increased under salinity stress and it was proportional with the salt concentration. Payam had the largest decrease (46.95%) in fresh weight caused by NaCl, while Jambo had the lowest decrease, 28.63%. Linear regression analysis revealed significant relationships between the estimated factors and fresh weight. The profiles of isoperoxidases were modified under stress conditions. Two isoforms, A1 and A2, were detected in all three varieties with different intensities. Under NaCl stress, isoperoxidases were strongly expressed and a third isoform, A3, was specifically found in variety Jambo suggesting that A3 is implicated in salt adaptation of this variety.
The present study was conducted to quantify the response of chlorophyll, protein concentration and electrophoretic patterns of leaf and root soluble proteins to increasing salinity in the rooting medium of three varieties (Payam, Kimia and Jambo) of sorghum (Sorghum bicolor L.) and to evaluate the usefulness of these parameters in identifying salt-resistant varieties. This work was carried out with five concentrations of salinity (0, 50, 100, 150 and 200 mM NaCl) and two sampling time points (sampling after 15 and 30 days salt treatment) using a split-split plot design with randomized complete block layout. With increasing salinity, the K+ concentration was found to decrease and the amount of Na+ and Na+/K+ increase significantly (P≤0.05) in roots and shoots. Chlorophyll a, b, total chlorophyll concentration and leaf and root soluble protein contents decreased with increasing salinity. The electrophoretic pattern of soluble proteins of cv. Jambo showed that after 15 days NaCl (200 mM) and 30 days NaCl (100 and 150 mM) treatment, a new polypeptide of molecular weight 50 kDa was expressed. The expression of this polypeptide might have been due to the plant adapting to NaCl via expression of a stress-resistant gene. This polypeptide was synthesized under salt stress and is suggested as a marker protein for salt adaptation.
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