Glutamate oxaloacetate transaminase in rice plant seedlings

Changes in glutamate oxaloacetate transaminase (L-aspartate : 2-oxoglutarate aminotransferase, EC 2.6.1.1; GOT) activity have been measured following ammonium assimilation in rice plant seedlings. GOT activity in the roots increases after ammonium treatment, whereas the activity in shoots is much less affected by the supply of ammonium. The isoenzymes of GOT in rice plant seedlings were separated by polyacrylamide gel electrophoresis. Two isoenzymes in the roots and 3 isoenzymes in the shoots were detected, but the isoenzymatic pattern does not change significantly during ammonium assimilation. GOT occurs in both the mitochondrial (m-GOT) and cytoplasmic fractions (s-GOT) from rice plant roots, and ammonium supply causes marked activation of m-GOT rather than s-GOT, accompanied by a specific increase of the m-GOT-I isoenzyme (slowly migrating band). Possible reasons for these changes and alterations in the ratio of the two GOT activities (m-GOT and s-GOT) during ammonium assimilation are discussed.