Understanding:
• Auxin efflux pumps can set up concentration gradients of auxin in plant tissue
Auxins are a group of hormones produced by the tip of a shoot or root (i.e. apical meristems) that regulate plant growth
- Auxin efflux pumps can set up concentration gradients within tissues – changing the distribution of auxin within the plant
- These pumps can control the direction of plant growth by determining which regions of plant tissue have high auxin levels
- Auxin efflux pumps can change position within the membrane (due to fluidity) and be activated by various factors
Auxin has different mechanism of action in the roots of plants versus the shoots of plants:
- In the shoots, auxin stimulates cell elongation and thus high concentrations of auxin promote growth (cells become larger)
- In the roots, auxin inhibits cell elongation and thus high concentrations of auxin limit growth (cells become relatively smaller)
The Role of Auxin Efflux Pumps on Growth Patterns in Plant Shoots
Understanding:
• Auxin influences cell growth rates by changing the pattern of gene expression
Auxin is a plant hormone and influences cell growth rates by changing the pattern of gene expression with a plant’s cells
- Auxin’s mechanism of action is different in shoots and roots as different gene pathways are activated in each tissue
In shoots, auxin increases the flexibility of the cell wall to promote plant growth via cell elongation
- Auxin activates a proton pump in the plasma membrane which causes the secretion of H+ ions into the cell wall
- The resultant decrease in pH causes cellulose fibres within the cell wall to loosen (by breaking the bonds between them)
- Additionally, auxin upregulates expression of expansins, which similarly increases the elasticity of the cell wall
- With the cell wall now more flexible, an influx of water (to be stored in the vacuole) causes the cell to increase in size
Mechanism of Auxin Action in Plant Shoots
