Auxins

What are growth hormones called

Plant growth regulators

What are plant growth regulators responsible for

Communication between different parts of the plant

Where are plant growth regulators produced

In tissues

What are the different means by which plant growth regulators move around the plant

• directly from cell to cell by diffusion or active transport

• Carried along with the contents of the phloem

How do plant growth regulators work

They bind to receptors on cell surface membrane or in the nucleus and initiate a signalling cascade.

What do auxins do

Causes cell elongation

What is the most common auxin

IAA (indole 3-acetic acid)

Where is auxin made

In the growing tips - meristems - of shoots and roots, where the cells are dividing.

What are the 3 stages in which growth occurs

• cell division via mitosis

• Cell elongation by absorption of water

• Cell differentiation

How does auxin work to cause elongation (7)

• Auxin binds to receptors in the cell surface membrane and activates proton pumps which pump H+ into the cell wall

• The acidification of the cell walls loosens the H-bonds between the cellulose microfibrils

• Expansins (proteins) also loosen the linkages between cellulose microfibrils and the surrounding substances.

• Potassium ion channels are stimulated to open, K+ diffuses into cytoplasm, increasing potassium ion concentration within the cytoplasm.

• Decreases water potential so water moves by osmosis into cell via aquaporins.

• Cells become more turgid and can elongate as a result of loosened bonds in cell wall.

• Disrupted bonds now reform and the wall becomes stable again.

Explain the role of auxin in cell elongation [8] {exam example}