13.6 Control of Plant Growth and Development Pages

Plant growth regulators Chemicals that direct plant growth and differentiation.

Tropism External stimulus directs the change in a plant’s growth Examples: phototropism, gravitropism, thigmostropism

Phototropism 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 The movement or growth of a plant in response to touch For 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

Photoperiod Flowering Leaves drop in autumn are triggered by changes in the duration of natural daylight

Gibberellins Promote cell division and elongation

Gibberellins Induces fruit production, fruit stems elongate providing more room for each grape

Gibberellin Produced by young shoot tissues and developing seeds. Accesses carbohydrate storage.

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