الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Salinity stress (EC: 0.55, 3.40, 6.77, and 8.00 mS/cm) induced retardation in the growth and productivity of rice plants. Such retardation was associated with reduction in K+ and K+/Na+ ratio in shoots and roots, Na+ buildup in shoots and roots, high electrolyte leakage and accumulation of malondialdehyde (MDA), total soluble sugars, sucrose, glucose, proline, total soluble proteins, enzymatic and non-enzymatic ntioxidants. Humic acid enhanced growth and productivity in Giza 177 and Giza 179 rice cultivars under non-saline and saline conditions. The humic acid-induced improvement in salt tolerance was associated with reduction of Na+ toxicity and oxidative stress, altering osmolytes concentration, and enhancing the activities of antioxidant enzymes. These results indicate that humic acid successfully reduced the salinity-induced plant damage, improved metabolism, and maintained active growth of rice under saline irrigation. The pairwise sequence alignment revealed the presence of few nucleotide differences in the promoter region of the proline metabolism-related genes including Δ1-pyrroline-5-carboxylate synthetase (P5CS), 2-Pyrroline-5-carboxylate reductase (P5CR), and Proline dehydrogenase (ProDH) in Giza 177 and Giza 179 rice cultivars. Through identifying cis-acting regulatory sequence, these nucleotide differences were found to affect on the expression of proline metabolism-related genes in both cultivars.