Effect of Nitrate and Ammonium on NADH-dependent Glutamate Dehydrogenase Activity of Detached Roots and Cotyledons of Citrullus vulgaris L.

Abstract

Roots and cotyledons of watermelon seedlings, grown in darkness for six days in a media with nitrate or ammonium as nitrogen source, were detached and incubated for 24 h in media of these nitrogen sources with or without actinomycin D or D-chloramphenicol. A continous protein synthesis at the organellular and the cytoplasmic level was required for maintaining NADH-GDH activity levels, regardless of the nitrogen source. When ammonium was present in the nutrient solution, the increase of activity observed seemed to be due to an elevated organellular and cytoplasmic protein synthesis in the cotyledons, while in the roots only the organellular synthesis was noted. The addition of nitrate decreased the GDH activity. In the cotyledons this effect seemed to be due to a decreased organellular protein synthesis, while in the roots, the effect was probably produced by an inactivation at the cytoplasmic level. Electrophoretic patterns of GDH varied depending on the plant organ and on the nitrogen source.