Influence of NaCl Salinity on the Behaviours of Malate, Isocitrate and Glucose 6-Phosphate Dehydrogenases in Growing Rice Seedlings in Relation to Salt Tolerance

Changes in the activity of the enzymes NAD⁺ -malate dehydrogenase, NADP+ - isocitrate dehydrogenase and NADP+ - glucose 6-phosphate dehydrogenase were compared in seedlings of rice (Oryza sativa L.) cultivars differing in salt tolerance, raised under increasing levels of NaCl salinity. During a 5–20 day growth period salinity caused marked increase in total and mitochondrial MDH activities in roots as well as shoots of salt tolerant cvs. CSR-1 and CSR-3 whereas in salt sensitive cvs. Ratna and Jaya a higher salinity level of 14 dSm⁻¹ NaCI was inhibitory to the enzyme in the seedlings of all the cultivars, G₆ PDH activity decreased under salinization. Results indicate possible impairment of pentose phosphate pathway and a more favourable route of NADPH generation via cytosolic ICDH under salinization. Further, salt tolerance ability appears to be associated with higher levels of total and mitochondrial MDH and ICDH activities in seedlings under salinization.