tapetal

Tapetal refers to the tapetum, a specialized nutritive tissue in the anthers of flowering plants. The tapetum lies at the inner boundary of the anther wall, surrounding the locules where microsporogenesis occurs, and provides materials essential for pollen development.

Origin and structure: The tapetal layer develops from archesporial cells associated with the developing anther. Depending on species, tapetal cells may persist as a distinct secretory layer or break down to form a plasmodial tissue that surrounds developing pollen.

Types and features: Two major tapetum types are commonly recognized. Secretory (glandular) tapetum consists of intact cells that remain metabolically active and secrete lipids, proteins, and sporopollenin precursors into the locule. Plasmodial (amoeboid) tapetum involves loss of cell walls and formation of a multinucleate plasmodium that supplies materials to the developing pollen.

Functions: The tapetum nourishes microspores during meiosis and microsporogenesis, supplies enzymes, lipids, and precursors for the pollen wall (exine and intine), and releases callase to degrade callose around tetrads, facilitating pollen release. It typically degenerates during late pollen maturation, making its timing critical for fertility. Abnormal tapetal development can cause male sterility in plants.

Significance: Because the tapetum plays a pivotal role in pollen viability and fertility, its biology is studied in botany, plant breeding, and cytology. Variation in tapetal development contributes to species diversity and has practical implications for hybridization and crop production.