A method of improving nitrogen stress tolerance in a plant comprising: (i) inhibiting ethylene synthesis in a plant by stably transforming a plant with a heterologous polynucleotide which reduces the expression of an ACC synthase upon expression of said heterologous polynucleotide; and (ii) growing said plant under nitrogen limiting conditions, whereby said heterologous polynucleotide is expressed and said plant demonstrates improved nitrogen stress tolerance compared to a control plant; wherein said heterologous polynucleotide comprises a nucleic acid selected from: (a) a nucleic acid encoding a transcript that is capable of forming a double-stranded RNA and mediating RNA interference of an ACC synthase nucleic acid, wherein said nucleic acid comprises: (i) a first nucleotide sequence comprising at least 21 contiguous nucleotides of an ACC synthase nucleic acid; and (ii) a second nucleotide sequence comprising the complement of said first nucleotide sequence, wherein the first and second nuceleotide sequences are separated by an intron; (b) a nucleotide sequence encoding a transcript that is capable of forming a double-stranded RNA and mediating RNA interference of an ACC synthase nucleic acid, wherein said nucleotide sequence comprises at least 21 contiguous nucleotides of SEQ ID NO: 1, 2, 3, 4, 5 or 6 and the complement thereof, separated by an intron; and (c) a nucleotide sequence encoding a transcript that is capable of forming a double-stranded RNA and mediating RNA interference of an ACC synthase nucleic acid, wherein said nucleotide sequence comprises at least 21 contiguous nucleotides of SEQ ID NO:2 or 5 and the complement thereof, separated by an intron. (i) inhibiting ethylene synthesis in a plant by stably transforming a plant with a heterologous polynucleotide which reduces the expression of an ACC synthase upon expression of said heterologous polynucleotide; and (ii) growing said plant under nitrogen limiting conditions, whereby said heterologous polynucleotide is expressed and said plant demonstrates improved nitrogen stress tolerance compared to a control plant; (a) a nucleic acid encoding a transcript that is capable of forming a double-stranded RNA and mediating RNA interference of an ACC synthase nucleic acid, wherein said nucleic acid comprises: (i) a first nucleotide sequence comprising at least 21 contiguous nucleotides of an ACC synthase nucleic acid; and (ii) a second nucleotide sequence comprising the complement of said first nucleotide sequence, wherein the first and second nuceleotide sequences are separated by an intron; (i) a first nucleotide sequence comprising at least 21 contiguous nucleotides of an ACC synthase nucleic acid; and (ii) a second nucleotide sequence comprising the complement of said first nucleotide sequence, wherein the first and second nuceleotide sequences are separated by an intron; (b) a nucleotide sequence encoding a transcript that is capable of forming a double-stranded RNA and mediating RNA interference of an ACC synthase nucleic acid, wherein said nucleotide sequence comprises at least 21 contiguous nucleotides of SEQ ID NO: 1, 2, 3, 4, 5 or 6 and the complement thereof, separated by an intron; and (c) a nucleotide sequence encoding a transcript that is capable of forming a double-stranded RNA and mediating RNA interference of an ACC synthase nucleic acid, wherein said nucleotide sequence comprises at least 21 contiguous nucleotides of SEQ ID NO:2 or 5 and the complement thereof, separated by an intron.