MOLECULAR PHYSIOLOGY OF LEGUME SEED DEVELOPMENT

Legume seed development is characterized by progressive differentiation of organs and tissues resulting in developmental gradientsA developmental gradient results from the gradual differentiation of different organs or within a single-seed organ and is reflected by heterogeneous populations of cells of different physiological age accumulating different amounts of substances, e.g., mRNAs, proteins, and starch. . The whole process is prone to metabolic control, and distinct metabolite profiles specify the differentiation state. Whereas early embryo growth is mainly maternally controlled, the transition into maturation implies a switch to filial control. A signaling network involving sugars, ABAabscisic acid , and SnRK1 kinases governs maturation. Processes of maturation are activated by changing oxygen/energy levels and/or a changing nutrient state, which trigger responses at the level of transcription and protein phosphorylation. This way seed metabolism becomes adapted to altering conditions. In maturing cotyledons photoheterotrophic metabolismPhotoheterotrophic metabolism occurs in green seeds in which specific photoheterotrophic plastids import sugars, are photosynthetically active, and produce oxygen, thereby supporting respiration and overall metabolic activity. improves internal oxygen supply and biosynthetic fluxes and influences assimilate partitioning. Transgenic legumes with changed metabolic pathways and seed composition provide suitable models to study pathway regulation and metabolic control. At the same time, desirable improvements of seed quality and yield may be achieved.