Transcript Plant responses to hormones

Plant responses to
hormones
What the spec says….
Types of plants hormone
1.
2.
3.
4.
5.
Auxins
Gibberellins
Cytokinins
Abscisic acid
Ethene
Cell division
Cell elongation
Promotors of growth
Differentiation
Initiation of organs
Inhibitors of growth /
Antagonists to growth stimulators
Growth substances can be…
 Synergistic
effects
– enhance each others’
 Antagonistic
– counteract each other
Auxin
 Indoleacetic
acid
 Causes elongation of cells
– Increases plasticity of cells
– Cell walls soften
– Cell becomes less turgid and take up
more water
– Cell expands
 Responsible
for phototropism
Phototropism experiments
Other activities of auxins
 Apical
dominance – apical bud
inhibits lateral (axillary buds)
– E.g. pruning stimulates axillary buds
 Formation
of lateral roots –
stimulates INITIATION of lateral
roots and adventitious roots
– E.g. napthalene acetic acid (NAA)
– Indole butyric acid (IBA)
More auxin functions
 Abscission
of leaves and fruit
 Abscission = falling of fruit and
leaves
 IAA – delays early stages, promotes
later stages
– Stimulates ethene production
– Ensure fruit stays on trees until harvest
Even more auxin functions
 Fruit
development
– Produced in pollen & developing seed
– Stimulates fruit development after
fertilisation
 Used
 Weed
in production of seedless fruits
killers
– 2,4-D causes abnormal growth of Dicots
(e.g. dandelions) monocots are
unaffected
Giberellins
 Stem
elongation in dwarf plants
– E.g. dwarf peas
 Bolting
of long day plants when the
days are short i.e. cause them to
flower
 Overcome lack of cold period
required for flowering in long day
plants


A wild type rice plant
(left) compared to a
semidwarf transgenic
plant (right)
containing the gai
mutant allele.
The gai mutant allele
confers giberellin
insensitivity upon the
transgenic plant, and
causes its reduced
stature.
More giberellins
 Fruit
development
– Stimulates growth of fruit stalk
– Delays senescence (aging)
 Seed
germination – stimulates
 Stimulate α – amylase production in
seeds, improves malt yields from
barley
Cytokinins

Produced by meristemic tissue
– Apices of roots and shoots
Development of roots, shoots and lateral
buds
 Cell enlargement
 Maturation of chloroplasts


Dependant on auxin for function

Cytokinins are
commonly used to
stimulate shoot
initiation in culture
as is shown by
shoot/bulblet
formation on bulb
scales of Bowiea
volubilis.
Benzyladenine was
used here to stimulate
shoot growth
Abscissic acid
 Inhibit
/ alter growth
 Linked to environmental stress
– Seeds can become dormant
– Abscission of leaves, flowers and fruits
– Close stomata in times of water
deficiency
Ethene (ethylene)
 Promotes
ripening of fruits
 Promotes abscission (auxin prevents
it)
– Abscission layer
 Antagonistic
to auxin