Salinity is one of the major environmental factors limiting crop productivity. For this reason, two greenhouse experiments were conducted in Faculty of Agriculture, Cairo University, Egypt, during the year 2015 using two rice varieties to evaluate the effects of various levels of osmotic stress caused by polyethylene-glycol 6000 (PEG) and NaCl. Furthermore, it was tested whether the inhibitory effect of salinity on growth, sodium and chloride concentration by two different varieties was greater under NaCl or PEG treatment. The first experiment was undertaken to separate osmotic and ionic aspects of salinity damage to rice (Oryza sativa L.).Seedlings of IR28 (salt-sensitive) and Nona Bokra (salt-tolerant) rice varieties were transferred to salinized nutrient solution containing 85 mol m-3NaCl (-3.0 bars) with or without   PEG 6000 (-2.0 bars, 45 gL-1).  Plants were grown up to 30 days in the salinized solutions. The second experiment was designed to determine the effect of salinity (85 mol m-3NaCl) with or without PEG 6000 (-0.5 bar, 11 g L-1)on growth, uptake and transport of sodium and chloride in two rice varieties differing in salt tolerance.  The results indicated that survival of salt-tolerant variety (Nona Bokra) was increased significantly by adding PEG (-2.0 bars). The addition of PEG also reduced the rate of death of rice plants compared with NaCl alone. Also, data showed that PEG 6000 (0.5 bar, 11 gL-1) reduce sodium concentration in root of IR28 and   Nona Bokra but its effect upon sodium concentration in shoot of the two varieties was more pronounced than the reduction of Na+ concentration in root.  Highly significant differences were obtained between zero and 11 gL-1 PEG. The result of this study is strongly indicated that addition of PEG dramatically lessened the toxicity of NaCl to rice seedlings.

Salinity is a stress factor affecting the production of crop in many regions.  Calcium can reduce Na+ transport to shoots in rice. Two greenhouse experiments were conducted in Faculty of Agriculture, Cairo University, Egypt, during 2015 growing season of rice to evaluate the effect of different calcium concentrations on survival percent along with uptake of Na+ and Cl- ions by two varieties of rice (Oryza sativa L.) differing in salt-tolerance. The first experiment was undertaken to study the effect of different calcium concentrations on survival percent of IR28 (salt-sensitive) and Nona Bokra (Salt-tolerant) seedlings which were transferred to salinized nutrient solution containing 0.5% NaCl and a variable calcium concentrations at 4, 40, 100 and 200 ppm; plants were grown up to 40 days. The second experiment investigated the effect of different calcium concentrations on growth, uptake and transport of Na+ and Cl- ions in the two rice varieties differing in salt-tolerance. The seedlings were transferred to salinized nutrient solution containing 0.5% NaCl and calcium ion concentrations at two levels, 4 and 40 ppm. Plants were harvested at 0, 1, 3, 5 and 7 days from salinization. The results indicated that the salt-tolerant variety (Nona Bokra) survived for more than 40 days under exposure to 0.5% NaCl when calcium concentration of the culture solution ranged from 40 to 200 ppm Ca++. The low calcium ion concentration (4 ppm) depressed the growth of plants at 5 and 7 days after salinization.  In Nona Bokra, the shoot had less sodium and Cl than the root. This implies that the salt tolerance of Nona Bokra may be attributed to the restricted translocation of Na+ and Cl- from the root to the shoot. Sodium as well as cloride content in the shoot of IR28 was more than twice that of Nona Bokra.  An adequate amount of Ca+2 tended to lower the salt injury caused by high levels of salinity in rice plants. The effect of calcium ion on salt tolerance varied greatly between Nona Bokra and IR28 varieties.