Plant Growth Regulators - horticulturebc.info Growth Regulators.pdf · Plant Growth Regulators A...
Transcript of Plant Growth Regulators - horticulturebc.info Growth Regulators.pdf · Plant Growth Regulators A...
Plant Growth Regulators
A hormone is a naturally produced chemical synthesized in one part of
the plant and then travels to another part where it effects growth and
development. There are five main groups:
Auxin or Indole Acetic Acid (IAA)
Gibberellin or Gibberellic Acid (GA)
Cytokinin (Ck)
Ethylene (C2H4)
Abscisic Acid (AbA)
Hormones discovered more recently include salicylic acid, jasmonates,
brassinolides, etc.
Plant growth regulators are man-made chemicals applied to plants to
produce a desired effect (some are chemically identical to hormones).
https://en.wikipedia.org/wiki/Plant_hormone
Phototropism: shoots bend towards light due to auxin migrating to darker side of stem.
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Light source
Gibberellic acid and low light levels cause stretching due to the elongation of internode cells. Plant Growth Regulators © KPU.ca/Hort
Effects of gibberellic acid and low
light on bean seedlings and petunia.
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Auxin regulates apical dominance: pinching/ shearing plants will result in more branches. Plant Growth Regulators © KPU.ca/Hort
Senescence (aging) and dormancy: Ethephon causes plants to release ethylene and senesce faster.
Control
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Control
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Senescent parts due to Ethephon spray abscise faster due to more ethylene gas being released.
Leaf abscission: occurs when auxin levels decrease and ethylene levels increase.
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A separation layer
forms in the abscission
zone where the petiole
joins the stem.
Fruit and flower part drop: ethylene released from apple cause separation layer formation.
Control
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Ethephon can also be used to de-green citrus fruits, and to ripen bananas or tomatoes. Plant Growth Regulators © KPU.ca/Hort
Shoot proliferation in tissue culture: high cytokinin and auxin level promotes shoot growth.
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Effect of cytokinin (e.g. Benzyl Adenine) to Auxin (IAA) levels on African violet in culture.
BA >> IAA
BA << IAA
Synthetic auxin (e.g. 0.1-0.8% IBA) can be used to stimulate adventitious rooting on cuttings.
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Under watered plants are stressed and have stomata closed more often. Why?
Under-watered
Under-
watered
Under-
watered
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Under-
watered
Auxins
Cell enlargement, role in apical dominance
Gibberellins
Cell (internode) elongation, seed germination
Cytokinins
Cell division, delays senescence
Abscisic Acid
Promotes dormancy, stomatal regulation
Ethylene
Fruit ripening, senescence, organ abscission
Summary: Main Effects of Plant Hormones (and related PGR’s)