The nucellus is a vital tissue found within the ovule of a flowering plant, serving as the central, nutritive component that surrounds and supports the developing embryo sac.
Understanding the Nucellus in Detail
The nucellus is primarily a mass of parenchymatous tissue. Parenchymatous tissue consists of living, thin-walled cells that are often involved in various plant functions, including storage, photosynthesis, and secretion. In the context of the nucellus, these cells are rich in food reserves and play a crucial role in providing nourishment.
Located as the central part of an ovule, the nucellus is surrounded by the integumentary layers. These integuments are protective coverings that will eventually develop into the seed coat after fertilization. Crucially, the nucellus encloses the embryo sac, which is also known as the female gametophyte. The embryo sac contains the egg cell that will be fertilized to form the embryo.
Key Characteristics of the Nucellus
To summarize, the nucellus can be characterized by several key features:
- Tissue Type: It is primarily composed of parenchymatous tissue, known for its storage and nutritive functions.
- Location: The nucellus occupies the central region of a plant's ovule, which is the structure that contains the female reproductive cells and develops into a seed after fertilization.
- Enclosure: Its primary role is to surround and enclose the embryo sac (the female gametophyte), which houses the egg cell.
- Protection: It is itself surrounded by the integumentary layers, which offer protection and later form the seed coat.
Primary Role and Significance
The most significant function of the nucellus is to provide nutrition to the developing embryo sac. Before fertilization, it supplies the necessary nutrients for the growth and maturation of the female gametophyte. After fertilization, as the zygote develops into an embryo, the nucellus continues to serve as a food source, contributing essential nourishment for the early stages of embryo development. In most plants, the nucellus degenerates as the seed matures, its nutrients consumed by the developing embryo or endosperm. However, in some plants, remnants of the nucellus may persist in the mature seed as a nutritive tissue called the perisperm.
