Method of selectively producing male or female sterile plants

A method of producing male or female sterile plants comprising the steps of:

• a) transforming plant material with a polynucleotide which encodes at least one enzyme which reacts with a non-phytotoxic substance to produce a phytotoxic one, wherein the enzyme is a D-amino acid oxidase and is selected from the group comprising SEQ ID NO:12, SEQ ID NO:
• 13, SEQ ID NO:
• 14, SEQ ID NO:
• 15, SEQ ID NO:
• 16, and SEQ ID NO:
• 17, and comprises a lysine at the position in its sequence corresponding to residue 58 of the wild-type D-amino acid oxidase sequence from Rhodotorula gracilis, and is expressed preferentially in either male or female reproductive structures;
• b) regenerating the thus transformed material into a plant;
• c) applying to the plant, up to the time of male or female gamete formation and/or maturation, a non-phytotoxic substance, wherein the non-phytotoxic substance is characterized as a D-alpha amino acid, or a peptide derivative of a non-protein D-alpha amino acid, so that said enzyme reacts with the non-phytotoxic substance to provide for the production of a phytotoxic one which selectively prevents the formation of or otherwise renders the said gametes non-functional wherein the plant is male or female sterile.