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Plant hormones and growth regulators

• Hormones– Auxins– Cytokinins– Gibberellins (GA)– Ethylene (ethene)– Abscisic acid (ABA)

• Other growth regulators– Brassinosteroids– Salicylic acid (SA)– Jasmonic acid (JA)– Systemin

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Auxin role:http://www.youtube.com/watch?v=zctM_TWg5Ik

Plant Hormone: Auxin

ALL Pea

Mustard and Corn

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Auxin regulates apical dominanceApical dominance = the growing apical bud inhibits the

growth of lateral (axillary) buds

Axillary buds are suppressed because of apical dominance

Removal of apical/ terminal bud induces growth of axillary buds

Applying IAA to cut surface prevents outgrowth of axillary buds

Phaseolus vulgaris (bean)

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Auxin: induces shoot elongation

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Auxin: Multiple Biosynthetic Pathways

IAN: Indole -3-acetonitrile Pathway

TAM: Tryptamine Pathway

IAM: Indole-3-acidamide Pathway

IPA: Indole-3-pyruvate pathway

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Polar Auxin Transport

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Auxin: Signal Transduction Pathway

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Dark side of Auxins

• The compound 2,4-D is still in use and is thought to be safe• 2,4,5-T banned by the EPA in 1979. • The Dioxin is an unavoidable contaminant produced in the manufacture of 2,4,5-T. Implicated in leukemia, miscarriages, birth defects, liver damage, and other diseases.

• Agent Orange was sprayed in Vietnam as a defoliant to deny ground cover to the Vietnamese army. The defoliant Agent Orange was a mix of 2,4-D and 2,4,5-T.

http://en.wikipedia.org/wiki/Auxin

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Growth Hormone: AuxinThings to Remember

• Plant hormones and growth regulators• Name the plant hormones and growth regulators• Role of auxin in plant development• Gravitropism, phototropism• Roles in Agronomy • IAA-myo-inositol hydrolyzed in endosperm and transported to

germinating coleoptile in free form• Polar auxin transport requires energy, independent of gravity• Tryptophan is the precursor for biosynthesis of Auxin• Consistent with Tryptophan synthesis in plastids, 1/3 of total IAA

is found in plastids.• Parthenocarpy• Auxin signal transduction pathway regulates expression of Auxin

responsive genes. • Genes AUX1 (auxin influx transport) and PIN1 (Auxin efflux

transport)

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Evidence:

• Isotope feeding

• Mutant analysis: the yucca mutant, but no auxin deficient mutant

The tryptophan- dependent pathway

Yucca

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