Biology – Control and coordination in plants | e-Consult

The statement "Auxin directly stimulates cell elongation by directly increasing the rate of cell wall synthesis" is incorrect. This is a misconception. Auxin does not directly increase the rate of cell wall synthesis. Instead, it initiates a series of events that lead to cell elongation by altering the properties of the cell wall.

The correct mechanism involves auxin triggering the activation of proton pumps in the plasma membrane. These pumps actively transport protons into the cell wall space, resulting in acidification. This acidification activates expansin enzymes. Expansins then weaken the hydrogen bonds between cellulose microfibrils in the cell wall, increasing its plasticity. This allows the cell wall to stretch under turgor pressure, leading to cell elongation. Therefore, auxin's role is indirect; it doesn't directly increase cell wall synthesis but rather modifies the cell wall's structure to make it more extensible.

The student's statement likely stems from a misunderstanding of the complex signaling pathways involved in plant growth. It's important to understand that auxin's action is a cascade of biochemical events, not a simple direct stimulation of cell wall synthesis.