plant met 2 hist

8/3/2019 Plant Met 2 Hist

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Plant Metabolism


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Plant Secondary Metabolites

Plants make a variety of less widely distributedcompounds such as morphine, caffeine, nicotine,menthol, and rubber. These compounds are theproducts of secondary metabolism, which is themetabolism of chemicals that occurs irregularly or

rarely among plants, and that have no knowngeneral metabolic role in plants.

Secondary metabolites or secondary compoundsare compounds that are not required for normalgrowth 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 discoveredalmost daily.


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Plant Secondary Metabolites

Secondary compounds are grouped into classesbased on similar structures, biosynthetic pathways,or the kinds of plants that make them. The largest

such classes are the alkaloids, terpenoids, andphenolics.

Secondary compounds often occur in combinationwith one or more sugars. These combination

molecules are known as glycosides. Usually thesugar is a glucose, galactose or rhamnose. Butsome plants have unique sugars. Apiose sugar isunique to parsley and its close relatives.


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Functions of Secondary Compounds

The most common roles for secondary compoundsin plants are ecological roles that governinteractions between plants and other organisms.

Many secondary compounds are brightly coloredpigments like anthocyanin that color flowers red

and blue. These attract pollinators and fruit andseed dispersers.

Nicotine and other toxic compounds may protectthe plant from herbivores and microbes.

Other secondary compounds like rubber andtetrahydrocannabinil (THC) from cannabis plantshave no known function in plants.


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Alkaloids

Alkaloids generally include alkaline substancesthat have nitrogen as part of a ring structure.More than 6500 alkaloids are known and are thelargest class of secondary compounds. They arevery common in certain plant families, especially:

Fabaceaepeas and beans Asteraceae - sunflowers

Papaveraceae - poppies

Solanaceaenightshade, 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 andcontribute 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 sixcarbon ring linked to an oxygen are calledphenolics.

Salicylic acid (basic part of aspirin) is a simplephenol.

Myristicin is a more complex phenol that providesthe flavor of nutmeg.

Flavonoids are complex phenolics. They are oftensold in health food stores as supplements to

vitamin C. The most commonly availableflavonoid is rutin from buckwheat.

Anthocyanins are a type of flavonoid that giveflowers 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 alsobe 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 tasteand odor.

Cyanogenic glycosides occur in several families of plants,

but are especially common in roses (Rosaceae) and peas(Fabaceae). They are sugar containing compounds thatrelease 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, thougha 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 byprimitive 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 ofplants and people,

including the influence

of plants on human

culture.

Oaxaca, Mexico


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Assyrian

Bas-relief

Of gods

PollinatingDate-palms


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Aristotle

384-322 BCE


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Theophrastus

370-285 BCE


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Page from Vienna Dioscorides

Arabic6th

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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More from Fuchs Herbal 1543


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Cover of

Gerards

Herbal

1597


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Title Page of John Rays


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Title Page of John Rays

Herbal - 1688


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Page from John Rays Herbal - 1688

plant met 2 hist

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