Physiology of Seed Plants

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Physiology of Seed Plants
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Regulating Growth and Development The Plant
Hormones

• Auxins
• Cytokinins
• Ethylene
• Abscisic Acid
• Gibberellins
• Molecular basis of Hormone Action

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Hormones

• Chemical signals that help both plants and
  animals regulate and coordinate metabolism,
  growth, and differentiation.
• Phytohormones- plant hormones

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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

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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

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Five classes of plant hormonesThe Classic Five

• Auxins
• Cytokinins
• Ethylene
• Abscisic acid
• Gibberellins

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Auxins

• Charles Darwin and Francis Darwin- The Power of
  Movement in Plants 1881

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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.