How does extensin help determine the final size of a plant cell?

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Cutaway illustration of a plant cell showing labeled internal structures including the nucleus, nucleolus, chloroplast, mitochondrion, vacuole, endoplasmic reticulum, ribosomes, Golgi apparatus, cell wall, and other key organelles. — Cell wall Cutaway drawing of a plant cell, showing the cell wall and internal organelles.

Extensin is a rod-shaped, hydroxyproline-rich glycoprotein that plays a critical role in regulating the final size of a plant cell.

These molecules are secreted into the cell wall toward the end of primary wall formation. Their structure, which resembles a bottle brush, allows them to be covalently cross-linked into a rigid mesh. This cross-linking process effectively halts cell growth. Consequently, plant cells can determine their ultimate size by regulating the specific timing of when this extensin cross-linking occurs.12