Plant Growth Hormones

Plant Growth Hormones

  • Plant hormones or phytohormones are naturally occurring substances that regulate the growth and development of plants.

Types of Plant Growth Hormones

  • The three main types of plant growth hormones are auxins, gibberellins, and cytokinins. Each has a different role within plant growth and development.

Auxins

  • Auxins are a type of plant growth hormone that control cell elongation and mediate growth responses to light and gravity.
  • They promote the elongation of cells in the stem and are involved in phototropism, the growth of a plant towards light.
  • Auxins also control geotropism, the plant’s response to gravity.
  • They stimulate the growth of roots in cuttings and are therefore used in root-powders.

Gibberellins

  • Gibberellins stimulate cell elongation and division, leading to growth in stem length.
  • They are also involved in seed germination, flowering, fruit development, and ageing.
  • Gibberellins are used commercially to increase the size of fruit and length of stems.

Cytokinins

  • Cytokinins stimulate cell division and are involved in bud development in shoots.
  • These hormones also help to delay the ageing of leaves.

Commercial Uses of Plant Growth Hormones

  • Plant growth hormones are often utilised in agriculture and horticulture.
  • Selective weed killers are developed from synthetic auxins, which cause the weeds to grow uncontrollably and then die.
  • Rooting powders contain auxins to stimulate root growth and are used when propagating plants from cuttings.
  • Fruit farmers often apply auxins and gibberellins to fruit trees to promote fruit set and growth.

Interaction Between Hormones

  • Plant growth and development is a delicate balance of these hormones interacting.
  • It is important to note that growth is not regulated by a single hormone, but rather, it’s the interplay of different hormones that dictate developmental processes.

Phototropism and Geotropism

  • Phototropism is the growth of a plant in response to light. Shoots are positively phototropic (grow towards light) and roots are negatively phototropic (grow away from light).
  • Geotropism is the growth of a plant in response to gravity. Shoots are negatively geotropic (grow away from gravity) and roots are positively geotropic (grow towards gravity).
  • Phototropism and geotropism are regulated by auxin distribution in the plant.