13.6 Control of Plant Growth and Development
Pages613-618
Photoperiod (page 608)
• Day length affects plants• For example: flowering
Plant growth regulators
Chemicals that direct plant growth and differentiation.
Tropism
• External stimulus directs the change in a plant’s growth
For example: Phototropism-the bending of a plant towards the light
Darwin’s phototropism experiment
Gravitropism
• Gravity affects growth• Roots grow downwards and shoots grow
upwards
Thigmotropism
• Objects influence plant growthFor example: rocks, trellises
Auxins
• Made in the shoot apical meristem• Stimulate cell elongation• Responsible for phototropism
Auxins cont…
• Herbicide• Simultaneously ripens fruit in orchards• Promotes apical dominance• Promotes rooting, growth of vascular
cambium and forms lateral buds
Apical dominance
• Removing apical meristem (auxins) allows lateral meristem to grow
Gibberellins
• Produced by young shoot tissues and developing seeds
• Promote cell division and elongation• Promote flowering and fruit production• Help to access carbohydrate reserves
cytokinins
• Promote cell division• Found in meristems, young leaves and
growing seeds• Stimulates lateral meristem growth• Slows cell aging
Ethylene
• Plant stress hormone• Drought…plant loses its leaves• Ozone…reduces plant yield• Lateral growth of roots around stones• Fruit ripening• Flower opening• Fruit and leaf drop
Abscisic Acid
• (ABA) inhibits growth• Maintains dormancy in leaf buds and seeds• Closes stomata to conserve water