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Osmotic Adjustment and Carboxylase Enzymes Activities of Three Rice Cultivars as Influenced by NaCl Levels
Dissertation Abstract:
Three rice cultivars, C4-63G, PB76-TB188 and IR8, were grown in sodium and chloride content, cell sap concentration, and activity of RuDP and PEP carboxylase.
Results showed that plant height, root length, number of tillers, and fresh and dry weight of shoot and root of the three rice cultivars increased at 0.1% but the decreased at 0.3% NaCl level. Increasing NaCl concentration increased the number of dead leaves and sodium and chloride concentrations in the shoot. IR8 exhibited the best growth and the highest proline content in the leaf blades.
At 2, 4, 6 and 8 days after NaCl treatment, IR8 plants showed the highest shoot osmotic pressure and the earliest osmotic adjustment, followed by PB76-TB188 and C4-63G. Osmotic adjustment of leaf sheath and stem was observed in IR8 and PB76-TB188 but not in C4-63G plants.
The salt treatments did not markedly affect chlorophyll content in the leaf blades. RuDP caboxylase in the leaf blades tended to increase in 0.1% NaCl treated plants. However, in 0.3% treatment, the RuDP carboxylase activity of PB76-TB188 and C4-63G tended to decrease while that of IR8 slightly increased. PEP carboxylase activity in all three cultivars tended to decrease with increasing NaCl levels form 0.1% to 0.3%.
The study clearly demonstrated the better ability of IR8 to adjust the shoot osmotic pressure. Furthermore, its main carboxylating enzyme, RuDP carboxylase, was less susceptible to salinity, hence its relative tolerance to saline conditions.