- When a plant responds to a directional stimulus by a growth movement it is known as tropism
- If growth is towards the stimulus it is known as positive tropism
- if growth is away from the stimulus it is described negative tropism
Tropisms
- Light
- response: phototropism: eg. shoots grow towards a light source (positively phototropic)
- Gravity
- Geotropism: e.g. shoots grow away from gravity (negatively geotropic) but roots grow in the direction of gravity (positively geotropic)
- Chemicals
- Chemotropisim: e.g. pollen tubes grow down style attracted by chemicals
- Water
- hydrotropism: e.g. roots grow towards water (positive hydrotropic)
Hormones
- Auxins e.g. IAA
- promote cell elongation
- inhibit growth of side shoots
- inhibit lead abscission (leaf fall)
- Cytokinins
- promotes cell division
- Gibberellins
- promotes seed germination and growth of stems
- Abscissic acid
- inhibits seed germinationa nd growth
- causes stomatal closure when plant is stressed due to low water availibility
- ethene
- promotes fruit ripening
Growing regions
- Growth only happens in particular places in plants called meristems
- where there a groups of immature cells capable of dividing
- apical meristems - located at the tip/apex of roots and shoots, lengthening growth
- lateral bud meristems - found in the buds, could give rise to side shoots
- lateral meristems - found in a cylinder near the outside of roots and shoots widening growth
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