coleoptiles

The coleoptile is a protective sheath that encloses the embryonic shoot in the seeds of most monocotyledonous plants, particularly grasses. It protects the plumule and the first leaf primordia as the seedling germinates and pushes through soil. The structure is a single tubular leaf that forms around the shoot apex and guides the young shoot toward the surface.

In cereal seeds such as wheat, barley, maize, and rice, the coleoptile sits above the root’s protective covering, the coleorhiza. The embryo proper includes an axis with the radicle, coleoptile, and plumule; the coleoptile develops around the plumule and assists the shoot’s emergence through soil until the first true leaves emerge above ground. The coleoptile is typically non-photosynthetic during subterranean growth, becoming green and photosynthetic only after exposure to light in some species.

During emergence, the coleoptile elongates and eventually ruptures at the soil surface, allowing the first true leaf to unfold. After surface emergence, photosynthesis by the newly formed leaves provides the seedling with energy for further growth. The term and concept are characteristic of monocots and are commonly applied to crops such as maize, wheat, rice, and oats; dicot seedlings generally lack a coleoptile.

The coleoptile is an important feature in germination biology and seedling establishment. Its length and integrity can influence successful emergence under soil obstacles and environmental conditions, making it relevant to crop breeding and agronomy.