Nitrate and nitrate are transported by different specific transport systems and by a bispecific transporter in Chlamydomonas reinhardtii.
Nitrate transport mutants from Chlamydomonas reinhardtii and strains derived from them upon transformation with plasmids containing the C. reinhardtii nar2/Nrt2;1 or nar2/Nrt2;2 genes have been used to study nitrate and nitrite transport systems. Mutants lacking nitrate assimilation clustered genes showed a high affinity nitrite transporter activity (system 3), which was subject to ammonium inhibition and appeared to be independent of a functional nar2 gene. Transformants carrying nar2/Nrt2;2 recovered a high affinity nitrate transporter activity (system 2) and showed nitrite transport activities with properties similar to those in nonrecovered high affinity nitrate transporter activity (system 1) together with a considerably enhanced nitrite transport activity. Nitrite transport mediated by system 1 was very sensitive to inhibition by nitrate at microM concentrations. Results strongly suggest that three nitrate assimilation related high affinity transport systems operate in C. reinhardtii: one specific for nitrite, a second one encoded by nar2/Nrt2;2 specific for nitrate, and another one encoded by nar2/Nrt2;1, which is bispecific for these two anions.
Galván
A
A
Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias, Universidad de Córdoba, Spain.
Quesada
A
A
Fernández
E
E
D000818:Animals; D001692:Biological Transport; D016825:Chlamydomonas reinhardtii / Q000378:metabolism*; D005796:Genes; D007700:Kinetics; D009154:Mutation; D009566:Nitrates / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D015183:Restriction Mapping; D014170:Transformation, Genetic
D009566:Nitrates; D009573:Nitrites