Tomato: The Apple of Peru

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West Coast, South America

Although the tomato is commonly associated with Italian food, the plant is native to the western coast of South America and was not introduced in Europe until the early 1500s when returning Spanish colonists brought it from the New World. However, North Americans believed tomatoes were poisonous until 1820, when Colonel Robert Gibbon Johnson disproved that myth during a public demonstration on the courthouse steps in Salem, NJ. In France, after the poison myth was dispelled, the people came to believe the tomato was an aphrodisiac and called it "pomme d'amour," or "love apple." Today, the typical American consumes about 80 pounds of tomatoes per year, and it is one of the most common plants grown in home gardens.

Typical Solanaceae  flower. (From Simpson and Ogorzaly, Economic Botany: Plants in Our World, 3d ed.,  2001, McGraw-Hill Companies. Reprinted by permission.)

Typical Solanaceae flower.

Tomatoes, Lycopersicon esculentum, are specifically native to the Andes region of Chile, Colombia, Bolivia, and Peru. It is believed that they were first domesticated in Mexico. Lycopersicon is Latin for "wolf peach," another common name for the tomato that hints at its perceived poisonous nature. Lycopersicon is a genus in the Solanaceae family, commonly referred to as the deadly nightshade family because it has many poisonous members, several of which produce toxic alkaloids. Among the 90 genera and almost 3,000 species of the Solanaceae are the potato (Solanum tuberosum); paprika, chilies, green peppers, and red peppers (all in the genus Capsicum); ornamentals such as petunia (Petunia sp.); the tobacco plant (Nicotiana); and the notoriously poisonous plants belladonna (Atropa belladonna) and jimson weed (Datura stramonium). The Solanaceae family is widely distributed throughout tropical and temperate regions. Although the plants occur on every continent, they are particularly concentrated in Australia, Central America, and South America. The flowers are bisexual, with petals fused at the base into a corolla with anthers attached to the corolla tube.

Botanically, the tomato is a fruit, even though the 1883 U.S. Supreme Court decided the tomato was legally a vegetable. This court case was brought about because New Jersey importer John Nix refused to pay an import tariff on his tomatoes, arguing that technically they
The tomato, a fleshy fruit. (From Stern, Introductory Plant Biology, 8th ed.,  2000, McGraw-Hill Companies. Reprinted by permission.)

The tomato, a fleshy fruit.

were fruits. While the Supreme Court justices agreed that botanically tomatoes were fruits, it was decided that commonly they were vegetables and therefore subject to the same tariff as other vegetables. By definition, a fruit is the mature ovary of an angiosperm, and the seeds are mature ovules. Although in some cases the fruit may develop and include some floral material other than the ovary (termed accessory fruits), other plant groups, such as the gymnosperms and ferns, cannot produce true fruits because they do not produce true flowers. Vegetables, on the other hand, are other parts of a plant, such as the leaves (lettuce), petiole (celery), roots (carrots), and inflorescences (broccoli).

After flowering, tomatoes require 50-60 days to reach fruit maturity. Although the full size of the fleshy fruit, called a berry, is attained in half that time, the later stage of maturity is marked by external color change with coinciding internal chemical changes. As the fruit changes from green to red, the acidity decreases, and both the sweetness and the vitamin A and C contents increase. The original green color is due to chlorophyll, the main photosynthetic pigment. As the chlorophyll breaks down, additional carotenoids are synthesized-lycopene, a red accessory pigment, and lesser amounts of -carotene, an orange accessory pigment. This change in internal and external morphology is due mainly to the presence of ethylene, a gaseous hormone discovered in 1901. Used in Hawaii to promote flowering in pineapples (Bromeliaceae) and to produce additional female flowers in some members of the Cucurbitaceae, ethylene is often associated with fruit ripening.
Tomato plant
              A Tomato plant.

Tomatoes are propagated from seeds. In temperate regions, they are generally started in greenhouses, hotbeds, or cold frames and then brought outside only when the danger of frost is past. Tomatoes are available year-round, with many crops field-grown in Florida, Texas, California, and Mexico as well as in greenhouses in the North. Many tomatoes are pickedew Jersey importer John Nix refused to pay an import tariff on his tomatoes, arguing that technically they while still green and artificially ripened on their way to market, generally in the
  (From Stern, Introductory Plant Biology, 8th ed.,  2000 McGraw-Hill Companies. Reprinted by permission.)

Harvesting a field with a
mechanical tomato harvester.

presence of ethylene.

Tomatoes are sold whole and fresh or canned and processed into soups, sauces, and ketchup. Those that are processed are mainly grown in the Midwest and the West, with the principal acreage in California. Most recently, hydroponic techniques are being used to grow tomatoes (and other crops) to full term in greenhouses. Hydroponics, originally practiced in the mid-1800s and reintroduced in 1937, grows plants in a water-based nutrient solution rather than in soil.

Genetically modified fruits and vegetables are being looked at as vehicles to deliver vaccines [for more information, see "A Needle or a Banana?"]. Along with the potato and the banana, the tomato is a potential candidate for use as one of these "edible vaccines."

References, Websites, and Further Reading

Levetin, Estelle, and Karen McMahon. 1999. Plants and society, 2d ed. New York: McGraw-Hill Companies, pp. 91-93.

Simpson, B.B., and Molly C. Ogorzaly. 2001. Economic botany: Plants in our world, 3d ed. New York: McGraw-Hill Companies.

Related Reading in Stern, Introductory Plant Biology, 8th Edition

Chapter 5: Roots and Soils
How Roots Develop; Root Structure, pp. 63-64

Chapter 6: Stems
Origin and Development of Stems, including petiole, pp. 85-87

Chapter 8: Flowers, Fruits, and Seeds
Differences Between Dicots and Monocots, including Table 8.1, pp. 129-30
Structure of Flowers, including anthers and corolla, pp. 129-32
Fruits, including fleshy fruits and berries, pp. 132-39
Accessory Fruits, p. 134

Chapter 10: Plant Metabolism
Chlorophyll, pp. 169-70
Absorption spectra of chlorophylls a, b, and carotenoids, Figure 10.7, p. 172

Chapter 11: Growth
Nutrients, Vitamins, and Hormones, pp. 188-89
Plant Hormones, pp. 189-95
Ethylene, pp. 193-94

Chapter 14: Plant Propagation and Biotechnology
Genetic Engineering or Recombinant DNA Technology, pp. 247-49
Awareness Box: Edible Vaccines from Genetically Engineered Fruits and Vegetables, pp. 252-53

Chapter 21: Introduction to Vascular Plants: Ferns and Their Relatives
Division Pterophyta-The Ferns, pp. 384-90

Chapter 22: Introduction to Seed Plants: Gymnosperms
General information, pp. 398-99
Reproduction, pp. 400-402

Chapter 23: Flowering Plants
Angiosperms, pp. 417-21

Chapter 24: Flowering Plants and Civilization
The Nightshade Family (Solanaceae), pp. 450-51

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