16.1 Plant hormones and growth in plants

what are some examples of plant responses

• tropisms

• responses to touch

• responses to herbivory

• responses to abiotic stress

what are the 4 important plant hormones

auxins

gibberellin

ethene

ABA (abscisic acid)

what are some examples of plant responses

• tropisms

• responses to touch

• responses to herbivory

• responses to abiotic stress

what are the 4 important plant hormones

auxins

gibberellin

ethene

ABA (abscisic acid)

what are some roles of auxins

• control cell elongation

• prevent leaf fall (abscission)

• maintain apical dominance

• involved in tropisms

• stimulate the release of ethene

• involved in fruit ripening

what are some roles of gibberellin

• cause stem elongation

• trigger the mobilisation of food stores in a seed at germination

• stimulate pollen tube growth in fertilisation

what are some roles of ethene

• causing fruit ripening

• promotes abscission in deciduous trees

what are some roles of ABA (abscisic acid)

• maintains dormancy of seeds and buds

• stimulates cold protective responses e.g antifreeze production

• stimulates stomatal closing

define tropisms

A tropism is a growth movement of a part of a plant in response to a directional stimulus

how do seeds germinate

• when seeds absorbs water the embryo is activated and begins to produced gibberellins

• they stimulate the production of enzymes that break down food stores in the seed (found in the cotyledons in dicot seeds and endosperm in monocot seeds)

• the embryo plant uses the food sources to produce ATP so it can grow and break through the seed coat

• evidence suggests that gibberellins witch on genes which code for amylases and proteases (the digestive enzymes required for germination) as well as that ABA acts as an antagonist to gibberellins (interferes with the action of gibberellin and the it is the relative level of both hormones which determine when the seed will germinate

what is the growth of plant shoot after the seed has germinated

determined by number of plant hormones

where are auxins produced

made in cells at the tip of the roots and shoots and in the meristems

what does the effect of auxins depends on

it depends on its concentration and any interactions it has with other hormones

what effects can auxins have on plant growth

stimulate the growth of the main apical shoot

suppress the growth of lateral shoots (results in apical dominance)

low concentrations of auxins promote root growth

what else do gibberellins do other than germination of seeds

they are also important in the elongation during growth