In one aspect, there is provided a mutant, non-naturally occurring or transgenic plant cell comprising: (i) a polynucleotide comprising, consisting or consisting essentially of a sequence encoding a member of the CLC family of chloride channels and having at least 60% sequence identity to SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:3 or SEQ ID NO:4 or SEQ ID NO:10 or SEQ ID NO:11； (ii) a polypeptide encoded by the polynucleotide set forth in (i)； (iii) a polypeptide comprising, consisting or consisting essentially of a sequence encoding a member of the CLC family of chloride channels and having at least 60% sequence identity to SEQ ID NO:5 or SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO:12 or SEQ ID NO:13 or SEQ ID NO:14； or (iv) a construct, vector or expression vector comprising the isolated polynucleotide set forth in (i)； and wherein the expression or activity of the polynucleotide or the polypeptide is modulated as compared to a control plant and wherein the nitrate levels in the mutant, non-naturally occurring or transgenic plant containing the mutant, non-naturally occurring or transgenic plant cell are modulated as compared to the control plant containing the control plant cell.En un aspecto, se proporciona una célula vegetal de existencia no natural o transgénica, mutante, que comprende: (i) un polinucleótido que comprende, consiste de o consiste esencialmente de una secuencia que codifica un miembro de la familia CLC de canales de cloruro y que tiene al menos 60% de identidad de secuencia con SEC ID NO: 1 o SEC ID NO: 2 o SEC ID NO: 3 o SEC ID NO: 4 o SEC ID NO: 10 o SEC ID NO: 11； (ii) un polipéptido codificado por el polinucleótido establecido en (i)； (Iii) un polipéptido que comprende, consiste de o consiste esencialmente de una secuencia que codifica un miembro de la familia CLC de canales de cloruro y que tiene al menos 60% de identidad de secuencia con SEC ID NO: 5 o SEC ID NO: 6, o SEC ID NO: 7 o SEC ID NO: 12 o SEC ID NO: 13 o SEC ID NO: 14； o (iv) una cons
