Effect of Different Nitrogen Sources and Plant Growth Regulators on Glutamine Synthetase and Glutamate Synthase Activities of Radish Cotyledons

The effect of different nitrogen sources – KNO3, NH4NO3 and NH4Cl – on glutamine synthetase and glutamate synthase activities of radish cotyledons (Raphanus sativus L.) in the presence or absence of light was investigated. The plants were treated with different phytohormones viz. Kinetin (KN), gibberellic acid (GA) and abscisic acid (ABA). In dark ammonia supplementation was effective in promoting glutamine synthetase activity in all the treatments, whereas, KNO3 was effective only in light in dH2O, GA and ABA treatments. In dark NH4NO3 promoted the glutamate synthase activity in dH2O while the activity was more with NH4Cl in KN treated seedlings. GA had no effect, while low concentration of all nitrogen sources promoted the activity in ABA treated seedlings. The activity was less in light as compared to dark grown seedlings Varying levels of NADH-glutamate synthase activity was discernible in all the treatments and addition of ammonia promoted this activity to some extent. It is suggested that different energy status of the seedlings during light/dark or with hormonal treatments may affect the activity of this enzymes differently. However, it is suggested that changes in FdGOGAT should be studied before any definite conclusions can be drawn.