SEX4, starch and phosphorylation( Energy from the sun and carbon dioxide ...)

Energy from the sun and carbon dioxide fuel photosynthesis in plants and algae, making life on earth possible. Carbon that is fixed by plants is converted to starch and sucrose, which are utilized by plants for energy and to build biomass. Human evolution and society have been intimately tied to our exploitation of plant biomass for food, fuel, tools, and shelter. However, to be usable, the starch carbohydrate stored in plants must be broken down to component sugars. Some aspects of starch metabolism have been known for many years, but regulation of the process and exact physical mechanisms are still not well understood. With new information emerging from genome sequencing and mutational analyses, we are beginning to gain a better understanding of these complex and finely tuned processes. Such knowledge is especially critical as we struggle with issues of energy and food supply.

Some of the new molecular mechanisms and regulatory components in starch metabolism have been identified by Dr. Samuel Zeeman and his colleagues. Dr. Zeeman, of the Institute of Plant Sciences, ETH Zurich, in Switzerland, who is the 2007 recipient of the Charles Albert Shull Award, will be presenting this work at the opening Awards Symposium of the annual meeting of the American Society of Plant Biologists in Mrida, Mexico (June 27, 2:30 PM). Mutational and structural analyses by Dr. Zeeman and his colleagues have revealed that starch degradation in Arabidopsis leaves at night differs significantly from the versions traditionally described in textbooks. Specifically, mutations at the Starch Excess 4 (SEX4), Maltose Excess 1 (MEX1) and other loci produce plants unable to metabolize starch to a usable form.

When we use starch in the lab or cook with it, we tend to think of it as an amorphous mass, but it is really a complex, ordered substance. Starch consists of two polysaccharides (polymers of the simple sugar glucose)--amylopectin and amylose. Both ar
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