Auxin and elongation growth

• plant hormones (also known as plant growth regulators) are responsible for most communication within plants
• Auxins are a type of plant growth regulator that influence many aspects of growth, including elongation growth which determines the overall length of roots and shoots
• the principal chemical in the group of auxins made by plants is IAA (indole 3-acetic acid) and this chemical is often simply referred to as 'Auxin'
• Auxins are a class of plant hormones that regulate groowth in plants
• Auxin is synthesized in the growing tips of roots and shoots (in the meristems where cells are dividing)
• Growth in these meristems occur in 3 stages:

  • Cell division (Mitosis)
  • Cell elongation (water absorption)
  • Cell differentiation
• Auxin is involved in controlling growth by elongatiob
• Controlling growth by elongation

  • auxin molecules bind to a receptor protien on cell surface membrane
• Auxin stimulates ATPase proton pumps to pump hydrogen ions from cytoplasm into the cell wall (across cell surface membrane)
• this acidifies the cell wall (lowers PH)
• Activates protiens known as expansins which loosen the bonds between cellulose microfribrils
• At the same time, potassium ion channels are stimulated to open
• leads to increase in potassium ion conc. in cytoplasm, decreases the water potential of cytoplasm
• causes cell to absorb water by osmosis
• increases internal pressure of cell, causing cell wall to stretch
• cell elongates
• diagram