The raz1 mutant of Arabidopsis thaliana lacks the activity of a high-affinity amino acid transporter.
The raz1 mutant of Arabidopsis thaliana (L.) Heynh. has been selected as resistant to the toxic proline analogue, azetidine-2-carboxylic acid (2AZ). Seedlings of the mutant tolerated fivefold higher concentrations of 2AZ (ED50 = 0.25 mM) than the wild-type seedlings (EC50 = 0.05 mM). The mutant gene was found to be semi-dominant and the corresponding RAZ1 locus was mapped on chromosome 5 at 69.6 +/- 1.8 cM. The resistance to 2AZ could be fully and exclusively accounted for by the lower uptake rate of the proline analogue in the mutant. The influx of L-proline in roots of wild-type seedlings could be dissected into two components: (i) a component with a high affinity and a low capacity for L-proline (Km) approximately 20 microM, Vmax approximately 60 nmol.(g FW)-1.h-1) and also a high affinity for L-2AZ (Ki approximately 40 microM) and (ii) a low-affinity, high-capacity component (Km) approximately 5 mM: Vmax = 1300 nmol.(g FW)-1.h-1). Clearly, the raz1 mutation affects the activity of a high-affinity transporter, because the high-affinity uptake of proline in the mutant was at least fivefold lower than in the wild-type, whereas the low-affinity uptake was unchanged.
Department of Genetics, Flanders Interuniversity Institute for Biotechnology, Universiteit Gent, Belgium.
N
N
Verbruggen
A C
AC
Borstlap
M
M
Jacobs
M
M
Van Montagu
E
E
Messens
D026905:Amino Acid Transport Systems; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism*; D001383:Azetidinecarboxylic Acid / Q000031:analogs & derivatives / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002874:Chromosome Mapping; D017343:Genes, Plant; D009154:Mutation; D010940:Plant Proteins / Q000378:metabolism; D011392:Proline / Q000378:metabolism
D026905:Amino Acid Transport Systems; D002352:Carrier Proteins; D010940:Plant Proteins; D001383:Azetidinecarboxylic Acid; D011392:Proline