Accumulation of Metabolites during Seed Development in Trifolium repens L.

Abstract

Metabolite deposition during seed development was examined histochemically in Trifolium repens by light- and fluorescence microscopy. All endosperm haustorium at the chalazal pole of the embryo sac and wall protrusions in cell walls of the suspensor and the embryo sac suggest that transfer of metabolites from maternal to offspring tissue takes place primarily at these sites. This is further supported by prominent cutinization of the interpolar region of the embryo sac wall, accumulation of starch in integumental tissue at the embryo sac poles, and breakdown of interpolar endothelial cells. Decomposition of osteosclereid starch is followed by accumulation in the cellular endosperm and subsequently in the embryo parallel to endosperm degradation. The starch accumulates gradually inward from the subepidermal cells of the embryo to the stele. Protein bodies are formed in the vacuoles along the tonoplast, later to be cut off in vesicles released into the cytoplasm. At maturity the embryo is packed with protein and starch, but without lipid reserves. Phytin is observed in the protein bodies. The mature embryo is surrounded by a protein and starch containing aleurone layer which originates from the endosperm.