Intine of pollen grain is made up of:

Question

Accepted Answer

The correct option is 1: Cellulose and pectin.

To fully understand the structure of the pollen grain, a male gametophyte, we must consider its two distinct walls: the protective outer *exine* and the metabolically active inner *intine*. The question specifically focuses on the intine, which is the inner, delicate, and highly elastic layer lying immediately outside the plasma membrane of the pollen cytoplasm. This inner wall is composed primarily of **pecto-cellulose**, making the combination of **cellulose and pectin** the correct choice. As is common for many primary plant cell walls, *cellulose* forms the framework of structural microfibrils that provide the necessary tensile strength and shape. *Pectin*, a group of hydrophilic polysaccharides, fills the spaces between the cellulose microfibrils, acting as a flexible, gelatinous matrix or cement that allows for high flexibility. This composition is crucial because the intine's most significant function is to grow out through one of the germ pores as the **pollen tube**. For the pollen tube to penetrate the stigma and style and safely deliver the male gametes, the intine must be soft, non-lignified, and capable of rapid, substantial stretching and expansion, all properties facilitated by its pectic and cellulosic components.

The incorrect option is 2: Lipid and protein.
This combination describes the basic material of the cell's living contents, not the structural wall. Lipids, such as phospholipids and sterols, are the core structural components of the plasma membrane, which lies *inside* the intine, and are also stored as energy reserves within the cytoplasm. Proteins are found everywhere in the cell—as enzymes, transporters, and as a component of the cell membrane. Although the intine does contain small amounts of proteins, often in the form of glycoproteins that may be involved in recognition or serve as allergens, they are *not* the primary structural material. To say the intine is *made up of* lipids and proteins confuses the wall's structure with the cell's membrane and contents.

The incorrect option is 3: Pectin and lignin.
This option incorrectly substitutes cellulose with lignin. While *pectin* is undeniably a major component of the intine, *lignin* is a complex, rigid polymer that imparts extreme stiffness and waterproof qualities to plant parts, such as the secondary walls of xylem vessels or woody tissue. Lignin is essentially a hardening agent. Its inclusion in the intine would render the inner wall inflexible and stiff, completely preventing the necessary turgor-driven expansion required for the formation and growth of the pollen tube. The tough, resistant outer wall of the pollen grain, the exine, is instead composed of sporopollenin, a highly resistant material that is chemically unrelated to lignin or cellulose.

The incorrect option is 4: Lignin and lignans.
This option is incorrect as it pairs two components associated with rigidity or secondary plant metabolism. As discussed, lignin is a non-structural hardening agent for the intine, a delicate, primary wall. Lignans, a group of secondary metabolites, are diphenolic compounds often found in the plant's food reserves or defense systems, such as seeds or fibrous material. They are certainly not the foundational, long-chain polysaccharide polymers like cellulose that form the primary physical structure of the intine. Therefore, this option fails to represent the chemical nature or the biological requirements of the pollen grain's inner wall.