Abstract: Plants, particularly cereal plants, which have altered ability to synthesise starch are produced by inserting into the genome of the plant a gene encoding an enzyme of the starch biosynthetic pathway such that capacity to produce starch is improved or reduced. The gene encoding the enzyme ADP-glucose pyrophosphorylase has been isolated from wheat leaf and wheat endosperm tissue. The enzyme is essential to the biosynthesis of starch in plants. Addition of extra copies of the gene to a plant by transformation enhances starch production, increasing the food value of the crop. Conversely, insertion of a gene encoding mRNA antisense to the mRNA encoded by the endogenous ADP-glucose pyrophosphorylase gene will reduce starch production. cDNA sequences are provided which may be used to identify homologous sequences in other tissue and in other plants. The ADP-glucose pyrophosphorylase gene promoter may be used in the genetic manipulation of plants to alter their starch-synthesising ability.