Résumé
In animals and yeast, voltage‐dependent chloride channels of the CLC family play a role in basic cellular functions such as epithelial transport, plasma membrane excitability, and control of pH and membrane potential in intracellular compartments. To assess the function of CLCs in plants, we searched for CLC insertion mutants in a library of
Arabidopsis
lines transformed by
Agrobacterium tumefaciens
transferred DNA (T‐DNA). Using a polymerase chain reaction‐based screening procedure, an
Arabidopsis
line that carries a T‐DNA insertion within the C‐terminus of the
AtCLC‐a
coding sequence was identified. Progeny from this plant line,
clca‐1
, showed dramatically altered transcription of the
AtCLC‐a
gene. Plants homozygous for the
clca‐1
mutation exhibited normal development and a morphology indistinguishable from the wild‐type. However, their capacity to accumulate nitrate under conditions of nitrate excess was reduced in roots and shoots, by approximately 50%, while chloride, sulphate and phosphate levels were similar to the wild‐type. In addition, the herbicide chlorate, an analogue of nitrate, induced a faster and more pronounced chlorosis in mutant plants. Hypersensitivity to chlorate as well as decreased nitrate levels co‐segregated with the T‐DNA insertion. They were found at various time points of the
clca‐1
life cycle, supporting the idea that AtCLC‐a has a general role in the control of the nitrate status in
Arabidopsis
. Concordant with such a function,
AtCLC‐a
mRNA was found in roots and shoots, and its levels rapidly increased in both tissues upon addition of nitrate but not ammonium to the culture medium. The specificity of AtCLC‐a function with respect to nitrate is further supported by a similar free amino acid content in wild‐type and
clca‐1
plants
.
Although the cellular localization of AtCLC‐a remains unclear, our results suggest that AtCLC‐a plays a role in controlling the intracellular nitrate status.