Download 5.4 Plant Growth - Blyth-Biology11

Plant Growth and Development
(14.2)
5.4
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
• Produced in plants at
the apical meristem
• Cause apical
dominance; plant
grows upward with
few to no side
branches
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 rapid 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.
Learning Check
• Pg 595, Q 13-18
External Factors that Regulate
Plant Development
Tropism • a change in the growth pattern or
movement of a plant in response to an
external stimulus
Nastic Response
• Plant response to a stimulus independent of the
direction of the stimulus
• Examples
– Flower opening petals during the day and closing
them at night
– Mimosa plant
http://www.youtube.com/watch?v=g0LFBM3hOLs
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 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.
NUTRIENTS IN ORDER OF PRIORITY
• CO2 and H2O
 needed for photosynthesis!
• N2 (from organic material)
 needed to produce proteins,
nucleic acids, chlorophyll and leaf
growth
– NH3 from animal waste
– NO2 and NO3 from decayed
materials
– Nitrogen fixing bacteria contain
N2 gas and convert it to nitrates
• Others... (next slide)
NITROGEN CYCLE (DON’T
MEMORIZE!)
OTHER ESSENTIAL
NUTRIENTS
Nutrient
Function
Deficiency
Symptoms
K
Water balance,
protein synthesis
P
Ca
Mg
S
ATP (energy)
syntesis, mitosis, cell
division
Part of cell walls,
membrane
permeability
Part of chlorophyll
and coenzymes for
photosynthesis
Part of proteins
You tell me!
Brainstorm time!
OTHER ESSENTIAL NUTRIENTS
Nutrient
Function
K
Water balance,
protein synthesis
Deficiency Symptoms
Poor growth, weak
stems, yellowing leaves
P
ATP (energy)
Stunted growth, poor
syntesis, mitosis, cell seed/fruit development
division
Ca
Part of cell walls,
membrane
permeability
Part of chlorophyll
and coenzymes for
photosynthesis
Part of proteins
Mg
S
Stunted growth
Yellowing leaves
Stunted growth,
yellowing leaves
FERTILIZERS
Natural
Synthetic
Examples
Manure,
Man-made
compost, sludge, chemical cocktails
crop rotation
that contain
ammonia and other
nutrients
Advantage
No harmful
chemicals
May not always
get the correct
amount of each
nutrient
Disadvantage
Get exact nutrients
Costly, prone to
leaching and runoff
which alters
chemical balance
in water and soil