Molecular Approaches to Understand Sink-Source Relations in Higher Plants

Abstract

Growth and development of a plant is dependent upon the energy gained by fixing carbon dioxide into carbohydrates during photosynthesis. Primary sites for photosynthesis are leaf and to a much lesser extent stem tissues, whereas other organs such as roots, seeds or tubers do not contribute to carbon assimilation but rather totally depend on photo-synthetically active organs. Thus there is a net flow of carbohydrates from photosynthetically active tissues, representing the sources (defined as net exporters of fixed carbon) to photosynthetically inactive parts of the plant, representing the sinks (defined as net importers of fixed carbon). Sink-source relations are constantly adjusted to the developmental stage of the plant (Ho, 1988). Thus all parts of a seedling develo** from a seed or a seed tuber represent a sink, whereas the original seed respectively seed tuber represent the source nourishing the develo** seedling. Upon further plant development the mature leaves and to a lesser extent the stem tissue will become the major source of a plant whereas young leaves, roots and to some extent stem tissue represent major sinks. Upon seed respectively tuber setting, again a drastic change occurs as now these newly developed organs represent the major sinks in the plant.