Endosperm

Endosperm is a nutritious tissue formed inside the seeds of most flowering plants after fertilization. It develops as a result of double fertilization: one sperm fuses with two polar nuclei in the embryo sac to produce a triploid cell that divides to form the endosperm. In gymnosperms, by contrast, the seed's nutritive tissue is derived from the female gametophyte rather than from endosperm formation.

Development patterns: Endosperm development can be nuclear, cellular, or mixed. In nuclear type, nuclei divide without cell walls initially, creating a multinucleate mass, followed by cellularization that forms individual cells. In cellular endosperm, cell walls form early and the tissue develops with cells containing stored reserves. Many seeds show a combination or transitions between these modes.

Function and composition: The endosperm stores starch, lipids, and proteins that nourish the developing embryo. In some seeds the endosperm is largely consumed during maturation (especially in some tropical species, or the embryo becomes the main storage tissue); in others it remains as the primary storage tissue until germination. The maize endosperm is a prominent example of a starchy endosperm; in coconut, the liquid endosperm eventually solidifies to form the edible kernel.

Significance: Endosperm contributes to seed size, vigor, and germination success. It is a focus of agricultural breeding and plant developmental biology, with genetic and epigenetic regulation influencing its development and the allocation of resources between embryo and endosperm.