Plant Hormones

Auxins - A group of plant hormones that affect the growth and elongation of cells.

Phototropism - Growth in response to the stimulus of light.

Gravitropism - Growth in response to the stimulus of gravity.

Auxins are produced in meristem cells in shoot tips. They move away from light, letting the cells that contain them elongate, making the plant bend towards the light. This causes phototropism.

Auxins are also in the roots of the plant. This causes gravitropism, which makes the roots grow downwards into the soil.

Gibberellins - Helps seeds to germinate and start to grow roots and roots.

Ethene - A gas which helps fruit to ripen. Hormone Gas.

Plant hormones have many commercial uses:

• Selective Weedkiller  - Auxins - Disrupts growth patterns and causes rapid cell division and elongation. Plant will die from lack of nutrient needed for the new cells.
• Rooting Powder - Auxins - Causes developments of roots from cuttings.
• Controlling flower and fruit formations  - Gibberellins - Causes seed germination, making the plant flower earlier than usual. Increases stem length and number and size of the flowers.
• Producing seedless fruit  - Gibberellins - Makes the seed grow without the fertilisation of the gametes, causing no seeds.
• Controlling the ripening of fruit  - Ethene - Ripens the fruits quicker. Unripe fruit are easier to transport than ripe fruit, so ripening them with ethene gas is done nearer the time it's needed.