Introduction

Starch biosynthesis in storage organs and tissues has become the subject of investigations in numerous laboratories, following a period during which only a few laboratories displayed substantial interest in the topic. This historical lack of interest is surprising because not only do the cereals, with their starchy endosperms, together with starchy roots and tubers, feed the human population of the world and supply a major portion of the food for many domestic animals, but starch is also an important industrial commodity. More than 2000 consumable products have been made directly or indirectly from starch. Corn starch is the major source of starch industry in United States. Corn generates more than 20 billion a year in farm value. U.S. farmers planted over 73 million acres of corn (23.5% of all US crops Fig. 1). The world market for corn products manufactured from it, and input to its production continue to expand. The resurgence in interest may be attributed to a combination of factors. In addition to the reality mentioned above, for example, the academic community is realizing that intriguing questions about starch biosynthesis remained unsolved. The wet millers, who produce starch commercially, are interested in learning more about the genetic basis for starch properties. For example,the maize mutants, waxy (my) and amylose extender(ae), have for years been grown on extensive acreages for their unique starches.

Genetic engineering might allow production of additional unique starches by transgenic plants. It has already demonstrated the enhancement of total starch production in transgenic potato plants (1) through the transfer from E. coli of a mutant allele of the gene encoding the enzyme adenosine diphosphate glucose (ADPGlc) pyrophosphorylase (E.C. 2.7.7. 27 ). A basic knowledge of how this enzyme plays a key role in the regulation for glycogen synthesis in bacteria and starch synthesis in some plants is required to design such an approach, and this knowledge has been supplied largely by research in Preiss laboratory (see reference 2 for a comprehensive review). A more complete understanding of the entire process of starch synthesis is a prerequisite to any attempts to manipulate the process to our benefit. Hannah et al (3) emphasized this point in their discussion of possible biotechnological modification of polysaccharides.

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