A. Galvan et al., NITRATE AND NITRITE ARE TRANSPORTED BY DIFFERENT SPECIFIC TRANSPORT-SYSTEMS AND BY A BISPECIFIC TRANSPORTER IN CHLAMYDOMONAS-REINHARDTII, The Journal of biological chemistry, 271(4), 1996, pp. 2088-2092
Nitrate transport mutants from Chlamydomonas reinhardtii and strains d
erived from them upon transformation with plasmids containing the C. r
einhardtii nar2/Nrt2;1 or nar2/Nrt2;2 genes have been used to study ni
trate and nitrite transport systems. Mutants lacking nitrate assimilat
ion clustered genes showed a high affinity nitrite transporter activit
y (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 60
those in nontransformed cells. Transformants carrying nar2/Nrt2;1 rec
overed high affinity nitrate transporter activity (system 1) together
with a considerably enhanced nitrite transport activity. Nitrite trans
port mediated by system 1 was very sensitive to inhibition by nitrate
at mu M concentrations. Results strongly suggest that three nitrate as
similation related high affinity transport systems operate in C. reinh
ardtii: 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.