Transcript Physiology of Seed Plants

Physiology of Seed Plants
Regulating Growth and
Development: The Plant Hormones
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Auxins
Cytokinins
Ethylene
Abscisic Acid
Gibberellins
Molecular basis of Hormone Action
Hormones
• Chemical signals that help both plants and
animals regulate and coordinate
metabolism, growth, and differentiation.
• Phytohormones- plant hormones
Three basic elements of Hormones
1. Synthesis of the hormone in one part of
the organism
2. Transport of the hormone to another part
(target tissue)
3. Induction of chemical response
Phytohormones
• Produced in tissues or glands
• Very active in small quantities
– Pineapple Ananas comosus for example are
only 6 micrograms of indoleacetic acid (IAA) a
common plant hormone per kg of plant
material. (analogous to a needle in 20 metric
tons)
– Can stimulate or inhibit depends on chemical
structure and how it is read by the target
tissue
Five classes of plant hormones
The “Classic Five”
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Auxins
Cytokinins
Ethylene
Abscisic acid
Gibberellins
Auxins
• Charles Darwin and Francis Darwin- The
Power of Movement in Plants 1881
Additional chemicals used by
plants
• Brassinosteroids- naturally occuring polyhydroxyl
steroids (tissue growth)
• Salicylic acid- phenolic compound similar structure to
aspirin implicated in defense responses
• Jasmonates- class of compounds known as oxylipins
plant growth regulation and defense
• Polyamines- strongly basic molecules found in all
organisms (bacteria, fungi, animal, plants) are essental
for growth and development and affects cell division
• Systemin- a polypeptide functions as a long distance
signal to activate chemical defenses against herbivores.
• Nitric oxide (NO) serves as a signal in hormonal defense
responses.