This is an update of cereal endosperm development and the starch biosynthetic enzyme, ADP-glucose pyrophosphorylase, in particular. When the endosperm development is fully understood including the genetic control of cell identity, i.e. directing aleurone versus starchy endosperm cells, this should increase the potentials for altering the grain oil, proteins and starch content and optimize the grain for different uses. The starch biosynthetic enzymes, ADP- glucose pyrophosphorylase (AGPase), starch synthase (SS), starch branching enzyme (SBE) and debranching enzyme (DBE) have isoforms preferentially expressed in the seed. The ADP- glucose pyrophosphorylase is a rate-limiting enzyme, which makes it a good candidate for regulating the starch content. Since it has been shown that the allosteric regulation of AGPase may limit the rate of starch synthesis in plants,there is much interest of engineering a higher plant AGPase that is insensitive to allosteric regulation for use in plant breeding. Grain content can also be given new characteristics by introduction of new genes. Cereal promoters driving tissue specific gene expression in seeds can direct production of recombinant antibodies in the plant parts being harvested and in this way combine traditional agriculture and advanced genetic engineering. Our group is studying seed preferential expression directed by upstream regions of i.e. the LTP1, LTP2, B22E and AGPase genes.