Structurally composed of the glucose homopolymers amylose and amylopectin, starch is the main storage carbohydrate in vascular plants, and is synthesized in the plastids of both photosynthetic and non-photosynthetic cells. Its abundance as a naturally occurring organic compound is surpassed only by cellulose, and represents both a cornerstone for human and animal nutrition and a feedstock for many non-food industrial applications including production of adhesives, biodegradable materials, and first-generation bioethanol. This review provides an update on the different proposed pathways of starch biosynthesis occurring in both autotrophic and heterotrophic organs, and provides emerging information about the networks regulating them and their interactions with the environment. Special emphasis is given to recent findings showing that volatile compounds emitted by microorganisms promote both growth and the accumulation of exceptionally high levels of starch in mono- and dicotyledonous plants. We also review how plant biotechnologists have attempted to use basic knowledge on starch metabolism for the rational design of genetic engineering traits aimed at increasing starch in annual crop species. Finally we present some potential biotechnological strategies for enhancing starch content.

Centre of the Region Haná for Biotechnological and Agricultural Research Department of Cell Biology Faculty of Science Palacky University Šlechtitelů 11 CZ 783 71 Olomouc Czech Republic

Instituto de Agrobiotecnología Mutiloako etorbidea z g 31192 Mutiloabeti Nafarroa Spain

University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center 700 Experiment Station Road Lake Alfred FL 33850 2299 USA

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