Chapter 39.2, Problem 1CC

Summary Introduction

To discuss: The effect of Fusicoccin on the growth of “isolated stem sections”.

Concept introduction:

Stimulation of “plasma membrane proton (H⁺) pumps” of plant cells causes following changes:

1. 1. Decreases the cell wall pH
2. 2. Increases the membrane potential

1. 1. Changes followed by “decrease in cell wall pH”:

   Lowering pH raises acidity level on the cell wall which activates proteins called expansions. These expansions disrupt the hydrogen bonds. The bonds are found in between cell wall constituents and cellulose microfibrils. This loosens the cell wall.

2. 2. Changes followed by “increase in membrane potential”:

   Increased membrane potential promotes the ion transmission into the cell. This process initiates water absorption by osmosis. More amount of water simultaneously increases the turgor and which in turn increases the flexibility of cell wall. The increase in cell wall flexibility enables the elongation of the stem.