Plant Metabolism

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Plant Metabolism
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Plant Secondary Metabolites

• Plants make a variety of less widely distributed
  compounds such as morphine, caffeine, nicotine,
  menthol, and rubber. These compounds are the
  products of secondary metabolism, which is the
  metabolism of chemicals that occurs irregularly
  or rarely among plants, and that have no known
  general metabolic role in plants.
• Secondary metabolites or secondary compounds are
  compounds that are not required for normal growth
  and development, and are not made through
  metabolic pathways common to all plants.
• Most plants have not been examined for secondary
  compounds and new compounds are discovered almost
  daily.

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Plant Secondary Metabolites

• Secondary compounds are grouped into classes
  based on similar structures, biosynthetic
  pathways, or the kinds of plants that make them.
  The largest such classes are the alkaloids,
  terpenoids, and phenolics.
• Secondary compounds often occur in combination
  with one or more sugars. These combination
  molecules are known as glycosides. Usually the
  sugar is a glucose, galactose or rhamnose. But
  some plants have unique sugars. Apiose sugar is
  unique to parsley and its close relatives.

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Functions of Secondary Compounds

• The most common roles for secondary compounds in
  plants are ecological roles that govern
  interactions between plants and other organisms.
• Many secondary compounds are brightly colored
  pigments like anthocyanin that color flowers red
  and blue. These attract pollinators and fruit
  and seed dispersers.
• Nicotine and other toxic compounds may protect
  the plant from herbivores and microbes.
• Other secondary compounds like rubber and
  tetrahydrocannabinil (THC) from cannabis plants
  have no known function in plants.

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Alkaloids

• Alkaloids generally include alkaline substances
  that have nitrogen as part of a ring structure.
  More than 6500 alkaloids are known and are the
  largest class of secondary compounds. They are
  very common in certain plant families,
  especially
• Fabaceae peas and beans
• Asteraceae - sunflowers
• Papaveraceae - poppies
• Solanaceae nightshade, tomato
• Apocynaceae - dogbanes
• Asclepiadaceae - milkweeds
• Rutaceae - citrus

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Terpenoids

• Terpenoids are dimers and polymers of 5 carbon
  precursors called isoprene units (C5 H8).
• Terpenoids often evaporate from plants and
  contribute to the haze we see on hot sunny days.
  They are expensive to make they often take 2 of
  the carbon fixed in photosynthesis carbon that
  could otherwise be used for sugars.

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Phenolics

• Compounds that contain a fully unsaturated six
  carbon ring linked to an oxygen are called
  phenolics.
• Salicylic acid (basic part of aspirin) is a
  simple phenol.
• Myristicin is a more complex phenol that provides
  the flavor of nutmeg.
• Flavonoids are complex phenolics. They are often
  sold in health food stores as supplements to
  vitamin C. The most commonly available flavonoid
  is rutin from buckwheat.
• Anthocyanins are a type of flavonoid that give
  flowers red and blue pigments.

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More Phenolics

• Some phenolics form polymers.
• Tannins are astringent to the taste. They give
  dryness (astringency) to dry wines. They can
  also be used to tan leather. They often give
  water a tea-colored look. Tannins are common in
  pines and oaks.
• Lignin is a major structural component of wood.
  The exact structure of lignin is complex and not
  known.

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Minor Secondary Metabolites

• Mustard oil glycosides are nitrogen-sulfur
  containing compounds that occur in cabbage,
  broccoli, horseradish, watercress and other
  members of the mustard family (Brassicaceae).
  They give the group its characteristic taste and
  odor.
• Cyanogenic glycosides occur in several families
  of plants, but are especially common in roses
  (Rosaceae) and peas (Fabaceae). They are sugar
  containing compounds that release cyanide gas
  when hydrolyzed.
• Cardiac glycosides effect vertebrate heart rate.
  Especially common in milkweeds Asclepiadaceae.
• The parsley/carrot family Apiaceae is noted for
  having aromatic and poisonous 17 carbon
  polyacetylenes, though a few species have
  alkaloids like Coniium.

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Mustard Oil
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Cyanogenic Glycosides
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Cardiac Glycosides
Common Milkweed Purple Foxglove
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Apiaceae - Polyacetylenes
Water Hemlock
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Ethnobotany

• Old and New

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What is Ethnobotany?

• Ethnobotany is the study of plants used by
  primitive and aboriginal people. John W.
  Harshberger 1895

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What is Ethnobotany?

• A better definition is
• Ethnobotany is the study of the interactions of
  plants and people, including the influence of
  plants on human culture.

Oaxaca, Mexico
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Assyrian Bas-relief Of gods Pollinating Date-palms
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Aristotle 384-322 BCE
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Theophrastus 370-285 BCE
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Page from Vienna DioscoridesArabic 6th
Century
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Page from Arabic edition of Dioscorides herbal
1334
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Title page from Fuchs herbal 1543
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Page from Fuchs Herbal 1543
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More from Fuchs Herbal 1543
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Cover of Gerards Herbal 1597
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Page from Gerards Herbal - 1597
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Title Page of John Rays Herbal - 1688
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Page from John Rays Herbal - 1688