Transcript Growth Regulators

Growth Regulators
Original by Libby Astrachan
Modified by Georgia Agriculture Education Curriculum Office- July 2004
August 2008
Plant Hormones
• Natural (made by plants) – also called
hormones
• Synthetic (man made)
• Also called PGRs (plant growth regulators)
• Purposes: start growth, stop growth,
modify growth & development
August 2008
5 Known Plant Hormones:
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Auxins (ox ins)
Gibberellins (jib ber ill ins)
Cytokinins (site oh kine ins)
Ethylene (eth el een)
Abscisic acid (ab sis ick)
Hormones may act individually or together
August 2008
Auxins
• Stem elongation
• Produced in tips of
stems (“B” in photo)
• Migrate from cell to
cell in stems
August 2008
Phototropism – ability to bend
towards light
• Auxins - responsible
for plants bending
towards light.
• Auxins - move down
shaded side of the
stem and cause cells
to elongate
August 2008
Gravitropism (geotropism) – plant
response to gravity
• Auxins – responsible
for plant response to
gravity
• Auxins – move to
lowest side and cause
stem tissue to
elongate – stem
curves upwards
August 2008
Apical dominance
• Auxins – move down
the stem from the
terminal bud and
inhibit growth of side
shoots
August 2008
Pinching
• Pinching = removing
the terminal bud
• Pinching - stops flow
of auxins down the
stem and allows side
shoots to develop
• Produces bushy, wellbranched crops
August 2008
Root development
• Auxins encourage
root development in
cuttings
• Some plants produce
plenty of auxins to
make rooting cuttings
easy
• Other plants need
synthetic auxins such
as IBA
August 2008
Gibberellins
• Cell elongation and cell
division
• Stimulate development
of flowers (as in
“gibbing” camelias)
• Cause internodes to
stretch
• Produced in stem and
root apical meristems,
seed embryos, young
leaves
August 2008
Internode Elongation
• Gibberellins cause
internodes to stretch in
relation to light intensity.
• High light intensity = no
stretch
• Low light intensity = long
internodes. Leaves are
raised to capture light
August 2008
Problems with Internode
Elongation
• Greenhouse problem – plants spaced too
closely to one another
• Plants shade one another – results in
stretching, less compact plants, weaker
stems, loss in value $$$
• B-Nine is a growth regulator that inhibits
gibberellin and controls plant height in
bedding plants
August 2008
Cytokinins
• Cell division (used in tissue culture)
• Cell differentiation (used in tissue culture for plant organ
formation)
• Formation of callus tissue
• Delay aging process in plants
• Produced in roots
• Transported through xylem
• Still researched
August 2008
Cytokinins vs. Auxins
• In stems – auxins inhibit lateral shoots,
cytokinins promote lateral shoots
• In roots – Auxins promote root branching,
cytokinins inhibit root branching
• Work together to control cell differentiation
and cell division
August 2008
Ethylene Gas
• Colorless gas
• Produced in nodes of stems, ripening
fruits, dying leaves
August 2008
Ethylene exposure
• Thickens stems
• Breaks down
chlorophyll
• Weakens cell
membranes
• Softens cell walls
August 2008
The Holly and the Ethylene
August 2008
Abscisic Acid – The Plant Stress
Hormone
• Growth inhibiting hormone
• Responsible for seed dormancy
• Responsible for closing stomata during
drought
August 2008
Synthetic Growth Regulators
• Rooting Compounds –
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increase rooting %
speed rooting
increase number
and
quantity of roots
•
increase uniformity
of
roots
August 2008
Rooting compounds
• Liquid or mixed with talc
August 2008
Growth Retardants
• Widely used in the greenhouse industry
• Inhibit action of gibberellins on stem
elongation
August 2008
Goal of Synthetic Growth
Retardants:
• Compact plants
• More attractive
• Greener
August 2008
• Easier to transport
• Flowering NOT
affected
Application Guidelines
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Read label
Wear safety gear
Apply correct amount at correct time
Plant should be well-established
Apply uniformly as foliar spray or drench
Split into two half-strength applications
August 2008