ABSTRACT

This chapter focuses on the anatomical and physiological features of each specific sink "type." Sinks cells are classified into three categories—secreting, accumulating, and consuming. The mechanism of translocation through plasmodesmata is strongly related to source-sink relationships. The relationship between sink strength and assimilate supply is specific to each sink and is governed by supply and demand. The three sink types are distinguished by their cell type, the chemical composition of the "stored" sugar and the storage compartment, as well as the half-time of the storage molecule. Soluble-sugar-storing parenchyma cells share common distinguishing anatomical, physiological, and biochemical features. Polysaccharide-storing parenchyma cells are found in stems, roots, metamorphous organs, and seeds. Starch accumulation starts and many amyloplasts are formed, as is usually the case in legume seeds. Seeds and fruits change from consuming sinks during the developing stage to storage sinks upon maturation and cessation of cell division.