Effect of plant growth regulators and different nitrogen sources on NADP-isocitrate dehydrogenase activity of radish cotyledons

NADP-isocitrate dehydrogenase (NADP-ICDH) activity of radish (Raphanus sativus L.) seedlings pretreated with various plant growth regulators: KiN, GA, and ABA and different nitrogen sources viz. KNO3, NH4Cl and NH4NO3 in light and dark was investigated. ICDH activity was significantly higher in light than in dark; addition of different nitrogen sources reduced it to a greater extent in NO3 supplementation. Among hormonal treatment only KiN showed slight promotion with KNO3 and NH4NO3. On the other hand in light KNO3 and/or NH4NO3 promoted ICDH activity and among hormones, KiN significantly promoted the activity in KNO3 and NH4NO3 supplemented seedlings while ABA was effective in NH4CL. It is suggested that in non-photosynthetic tissues, NADP-ICDH provides both reductant and carbon skeleton for glutamate synthesis.