REGULATION OF GLUTAMATE-DEHYDROGENASE ACTIVITY IN RELATION TO CARBON LIMITATION AND PROTEIN CATABOLISM IN CARROT CELL-SUSPENSION CULTURES

Glutamate dehydrogenase (GDH) specific activity and function have been studied in cell suspension cultures of carrot (Daucus carota L. cv Ch antenay) in response to carbon and nitrogen supply in the culture medi um. The specific activity of GDH was derepressed in sucrose-starved ce lls concomitant with protein catabolism, ammonium excretion, and the a ccumulation of metabolically active amino acids. The addition of sucro se led to a rapid decrease in GDH specific activity, an uptake of ammo nium from the medium, and a decrease in amino acid levels. The extent of GDH derepression was correlated positively with cellular glutamate concentration. These findings strengthen the view that the function of GDH is the catabolism of glutamate, which under conditions of carbon stress provides carbon skeletons for tricarboxylic acid cycle activity .