Regulation via GAD levels
The different expression patterns of GAD mRNA and protein in different
Petunia organs suggest that GAD activity is transcriptionally
and translationally regulated34. Furthermore, Arabidopsis possesses
at least two GAD isoforms, one that is root-specific (GAD1) and
another (GAD2) that is present in all organs18,19. The GAD2 transcript
level, encoded protein and specific activity are higher in
plant leaves supplied with either 10 mM NH4Cl, 5 mM NH4NO3,
5 mM glutamate or 5 mM glutamine as the sole nitrogen source,
than in leaves treated with 10 mM KNO3 (Ref. 18). The impact of
other stresses on GAD expression has not been investigated.