How does endosperm nourish a developing angiosperm embryo?

In angiosperms, the endosperm serves as a specialized food-storage tissue that nourishes the developing embryo and the subsequent germinating seedling.12

This tissue is formed during double fertilization, a process unique to flowering plants, where one sperm nucleus fuses with two polar nuclei to create a triploid endosperm nucleus. This nucleus then undergoes mitotic divisions to develop into the nutrient-rich endosperm.12

The embryo accesses these stored reserves—which include starch, proteins, and lipids—in several ways:

• Direct Absorption: In many species, the cotyledons (seed leaves) act as absorbing organs that mobilize and withdraw nutrients from the endosperm.13
• Enzymatic Action: In grasses, the cotyledon is modified into a specialized structure called a scutellum, which secretes enzymes to break down and translocate stored materials to the growing embryo.3
• Transfer: During germination, the cotyledons penetrate the endosperm tissue to transfer nutritional products to the developing radicle and epicotyl.3

In some plants, the endosperm is fully absorbed by the embryo before maturity, with nutrients instead stored directly within the cotyledons.13