The cells of which of the following layers of the anther wall are multinucleated due to endomitosis ?

Question

Accepted Answer

The correct option is 4: Tapetum

The cells of the **Tapetum** are uniquely characterized by becoming multinucleated, a crucial adaptation for their essential role as the innermost, nutritive layer of the anther wall. The primary function of the tapetum is to provide nourishment, enzymes, and materials (like sporopollenin precursors) to the rapidly developing microspores, which later mature into pollen grains. This intense metabolic activity and massive synthesis of biomolecules require a high genetic expression level, which is achieved through abnormal nuclear divisions. **Endomitosis** is one such process where the chromosomes replicate, but neither the nuclear envelope breaks down (karyokinesis) nor does cell division (cytokinesis) follow, resulting in cells with multiple nuclei or a single large, polyploid nucleus. This increase in DNA content directly enhances the biosynthetic capacity of the tapetal cells, ensuring the timely and proper development of the male gametophyte. If tapetal cells fail to develop this multinucleate condition, it often leads to sterile or aborted pollen.

The incorrect option is 1: Nucellus

The **Nucellus** is an entirely different structure, representing the central mass of diploid, parenchymatous tissue within the ovule (the female reproductive organ), not the anther wall. Its role is to enclose and nourish the developing embryo sac (female gametophyte). Nucellus cells are typically uninucleated and diploid, consistent with standard somatic plant cells. While it is also a nutritive tissue, it achieves its function through normal metabolic activity and sometimes persists as a storage tissue called perisperm, but it does not undergo the endomitosis that characteristically leads to multinucleated cells in the tapetum.

The incorrect option is 2: Endothecium

The **Endothecium** is the layer situated immediately beneath the epidermis in the anther wall. Unlike the tapetum, its primary functions are protection and facilitating the **dehiscence** (splitting open) of the anther to release the mature pollen grains. This function is structurally supported by the development of characteristic **fibrous thickenings** made of alpha-cellulose on the radial and inner tangential walls of its cells. The cells of the endothecium remain uninucleated and their function is mechanical and structural, not primarily metabolic or nutritive, hence they do not undergo endomitosis to become multinucleated.

The incorrect option is 3: Middle layer

The **Middle layer** is composed of one to three layers of cells located between the endothecium and the tapetum. These layers are usually short-lived, serving a protective role early in anther development. They generally degenerate and are consumed to provide nutrients for the developing microspores as the anther matures. Like the epidermis and endothecium, the cells of the middle layer are standard somatic cells that possess a single nucleus and do not exhibit the nuclear division anomalies such as endomitosis or subsequent multinucleation.