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