Hormones in plants

• When seeds are dispersed, they fall any way in the soil
• It's important that the seed grows and the roots grow downward into the soil
• The shoot needs to grow upwards to coordinate with the light
• No matter which way the plant seed lands, the plant will grow the right way because the roots grew down in the direction of gravity and the shoots grew towards the light
• Plant responses are a result of plant hormones that coordinate/control growth
• The responses of plant roots/shoots to light/gravity is tropisms
• Phototropism


  Plant response to light
• Gravitropism


  Plant response to gravity
• These responses are controlled by a hormone Auxin
• The response occurs due to an uneven distribution of this hormone in the shoot or root, causing unequal growth rate
• Phototropism


  • Auxin moves from the side of the shoot where the light is to the unlit side
  • The cells on that side respond to the hormone by growing more, causing the shoot to bend towards the light
• Gravitropism


  • High levels of auxin make shoot cells grow more and inhibit growth of root cells
• Gibberellins


  Plant hormones that are important in initiating seed germination. They trigger breakdown of the food stores in the seed at the start of germination. They also stimulate the growth of plant stems.
• Ethene


  An unusual hormone because it's a gas. It helps control cell division.
• When taking cuttings of plant stem there won't be any variation in the offspring
• Taking plant cuttings


  1. Place the stem in specially prepared compost

  2. New roots will form at the base of the stem to form a new small plant
• Dipping the cut end of a root into rooting powder (containing Auxin)


  Increases the chances of success because the auxin stimulate growth
• Auxin


  Can also be used to make weak killers because the extra auxin can send the plant into rapid growth, killing it. Auxin only kills weeds because they are broad-leaf plants, so have a larger surface area so absorb more than narrow-leaved plants.
• Using gibberellins


  1. Brewing industry to end seed dormancy, speeding up the germination of the barley feeds used to make malt

  2. Promote flowering throughout the year

  3. Increase size of fruit
• Using ethene


  Control the ripening of fruit. Stored unripe fruit can be rapidly ripened to the perfect stage for sale when needed.