Effect of plant growth regulators and different nitrogen sources on glutamate dehydrogenase activity

Radish (Raphanus sativus L.) seedlings, treated with various plant growth r egulators (PGRs) [viz. kinetin (KiN), gibberellic acid (GA), and abscisic a cid(ABA)] were exposed to different nitrogen (N) sources in light and dark condition, and aminative (NADH) and deaminative (NAD(+)) glutamate dehydrog enase (GDH) activities were measured in cotyledons. A differential effect o f nitrogen sources, plant growth regulators, and light or dark condition wa s observed in all the treatments. The NAD-GDH (deaminating) activity in rad ish seedlings was only about 10% of aminating activity (irrespective of the PGR treatment). Except with abscisic acid, in all other treatments, either NAD-GDH or NADH-GDH activities were more in dark than in light. The aminat ion and deamination reactions also showed different ratios of activity unde r different N sources (KNO3, NH4Cl and NH4NO3). These data suggest the pres ence of isoenzymes or conformers of GDH, specific for-each tissue, whose ac tivities vary depending on the physiological condition of the tissue. Diffe rent energy status of the seedlings during light or dark condition or with PGR treatments may affect the GDH activity differently.