Transcript Growth Regulators

Growth Regulators
Original by Libby Astrachan
Modified by Georgia Agriculture Education Curriculum Office- July 2004
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
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
Auxins
• Stem elongation
• Produced in tips of
stems (“B” in photo)
• Migrate from cell to
cell in stems
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
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
Apical dominance
• Auxins – move down
the stem from the
terminal bud and
inhibit growth of side
shoots
Pinching
• Pinching = removing
the terminal bud
• Pinching - stops flow
of auxins down the
stem and allows side
shoots to develop
• Produces bushy, wellbranched crops
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
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
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
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
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
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
Ethylene Gas
• Colorless gas
• Produced in nodes of stems, ripening
fruits, dying leaves
Ethylene exposure
• Thickens stems
• Breaks down
chlorophyll
• Weakens cell
membranes
• Softens cell walls
The Holly and the Ethylene
Abscisic Acid – The Plant Stress
Hormone
• Growth inhibiting hormone
• Responsible for seed dormancy
• Responsible for closing stomata during
drought
Synthetic Growth Regulators
• Rooting Compounds –
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increase rooting %
speed rooting
increase number
and
quantity of roots
•
increase uniformity
of
roots
Rooting compounds
• Liquid or mixed with talc
Growth Retardants
• Widely used in the greenhouse industry
• Inhibit action of gibberellins on stem
elongation
Goal of Synthetic Growth
Retardants:
• Compact plants
• More attractive
• Greener
• 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