Transcript Control of Plant Development

Control of Plant Development
Plant growth regulators (PGRs) •
plant hormones that affect the rate
of division, elongation and
differentiation of plant cells
Five well-characterized groups of
PGRs • auxins, gibberellins,
cytokinins, abscisic acid and
ethylene
Auxins promote
elongation of cells,
stimulate growth and
ripening of fruit, and
also inhibit the
dropping of fruit and
leaves.
Synthetic auxins can
be used to stimulate
growth of fruit from
unpollinated plants,
resulting in, for
example, seedless
tomatoes.
Seedless tomatoes!
Gibberellins promote
cell division and
elongation.
Sometimes they cause
a process called bolting
where the stem of a
plant rapidly grows
taller before flowering.
Lettuce bolting after it has
been treated with
gibberellins.
Many dwarf varieties of
plants stay small
because they do not
produce normal levels
of gibberellin.
Cytokinins stimulate
cell divison and leaf
growth.
Commercially,
cytokinins are used to
extend the life of cut
flowers.
Abscisic acid’s main
role is to coordinate
responses to stress in
plants.
Usually it inhibits
growth.
Maple tree seeds. Some
seeds can remain dormant
for years and still be viable
in newfound hospitable
conditions.
It can induce
dormancy of seeds to
protect them from
harsh conditions and
also regulates rate of
transpiration.
Ethylene is a gas
produced in many of
the plant’s tissues.
It plays a role in flower
death, fruit ripening and
fruit loss.
Commercially, growers
can delay ripening of
fruit until they are about
to be sold by controlling
the levels of ethylene in
the fruit.
Tomatoes before
ripening. A spray of
ethylene would have
these ripe and red in no
time.
External Factors that Regulate
Plant Development
Tropism • a change in the growth pattern
or movement of a plant in response to an
external stimulus
Thigmotropism • a
change in the growth
pattern or movement
of a plant in response
to touch
For example, the
tendrils of pea plants
will grow around a
supporting structure at
the point of contact.
http://www.youtube.com/watch?v=dTljaIVseTc
Phototropism • a change in the growth pattern
or movement of a plant in response to light
For example, a plant growing in uneven light will
lean and bend its stem in order to become
better exposed to the light.
http://www.youtube.com/watch?v=zHe7y8cy-7Y
Gravitropism • a
change in the growth
pattern or movement
of a plant in response
to gravity
If plants could not
detect and respond to
gravity, their roots
would be as likely to
grow up into the air as
down into the ground.
This plant has been left to
grow upside down. You can
see in the picture that the
stem is trying to grow back
upwards and fight gravity.
Photoperiodism • plants in regions where
there are two or more seasons control their
reproductive cycles based on the duration of
daylight, a.k.a the photoperiod.
Plants flowering in the spring means the most
time available for seed and fruit development
before winter.
Trees dropping their leaves in the fall means
protection from the cold, dry conditions of
winter.