ISSN:
1432-2048
Keywords:
Aspartate aminotransferase (immunocytochemistry, subcellular fractionation)
;
Glutamate oxaloacetic transaminase
;
Medicago (root nodules, N2 fixation)
;
Nitrogen fixation
;
Root nodule
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Aspartate aminotransferase (AAT; EC 2.6.1.1) catalyzes the synthesis of the amino acid aspartate which, in alfalfa root nodules, serves as the immediate precursor of the primary N-transport compound, asparagine. The enzyme AAT may also be important in providing substrates for host-plant and bacteroid respiration. The enzyme occurs as two isoenzymes, AAT-1 and AAT-2, with AAT-1 more abundant in roots and AAT-2 predominant in root nodules. To further elucidate the role of AAT in root-nodule metabolism, subcellular fractionation and immunocytochemical methods were used to determine the intra- and intercellular localization of these two isozymes. Fractionation of nodule subcellular components showed that AAT-2 was localized in amyloplasts. Immunogold labelling with AAT-2 antibodies unequivocally confirmed this, showing that AAT-2 was localized in nodule amyloplasts and leaf chloroplasts. In root nodules, the density of immunogold labelling of infected cell plastids was almost four times that of uninfected cell plastids. The data suggest that aspartate biosynthesis in alfalfa root nodules occurs primarily in the plastids of infected cells.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01089036
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