第26章種子植物

Seed plants are the foundation of human diets across the world (Figure 26.22). Many societies eat almost exclusively vegetarian fare and depend solely on seed plants for their nutritional needs. A few crops (rice, wheat, and potatoes) dominate the agricultural landscape. Many crops were developed during the agricultural revolution, when human societies made the transition from nomadic hunter–gatherers to horticulture and agriculture. Cereals, rich in carbohydrates, provide the staple of many human diets. Beans and nuts supply proteins. Fats are derived from crushed seeds, as is the case for peanut and rapeseed (canola) oils, or fruits such as olives. Animal husbandry also consumes large quantities of crop plants.

Staple crops are not the only food derived from seed plants. Various fruits and vegetables provide nutrient macromolecules, vitamins, minerals, and fiber. Sugar, to sweeten dishes, is produced from the monocot sugarcane and the eudicot sugar beet. Drinks are made from infusions of tea leaves, chamomile flowers, crushed coffee beans, or powdered cocoa beans. Spices come from many different plant parts: saffron and cloves are stamens and buds, black pepper and vanilla are seeds, the bark of a bush in the Laurales family supplies cinnamon, and the herbs that flavor many dishes come from dried leaves and fruit, such as the pungent red chili pepper. The volatile oils of a number of flowers and bark provide the scent of perfumes.

Additionally, no discussion of seed plant contribution to human diet would be complete without the mention of alcohol. Fermentation of plant-derived sugars and starches is used to produce alcoholic beverages in all societies. In some cases, the beverages are derived from the fermentation of sugars from fruit, as with wines and, in other cases, from the fermentation of carbohydrates derived from seeds, as with beers. The sharing of foods and beverages also contributes to human social ritual.

Seed plants have many other uses, including providing wood as a source of timber for construction, fuel, and material to build furniture. Most paper is derived from the pulp of coniferous trees. Fibers of seed plants such as cotton, flax, and hemp are woven into cloth. Textile dyes, such as indigo, were mostly of plant origin until the advent of synthetic chemical dyes.

Lastly, it is more difficult to quantify the benefits of ornamental seed plants. These grace private and public spaces, adding beauty and serenity to human lives and inspiring painters and poets alike.

The medicinal properties of plants have been known to human societies since ancient times. There are references to the use of plants’ curative properties in Egyptian, Babylonian, and Chinese writings from 5,000 years ago. Many modern synthetic therapeutic drugs are derived or synthesized from plant secondary metabolites. Very often, the raw form of the plant or plant-based substance may be unusable even if it demonstrates helpful properties. For example, chaulmoogra oil was somewhat effective for treating leprosy, but it was difficult to apply and painful for patients. In 1915, Alice Ball (at only 23-years old), created a method for extracting the active ester compounds from the oil so that it could be absorbed by the body, creating a much more effective treatment without the negative side effects. The "Ball Technique" remained the preferred method until synthetic medicines replaced it decades later. It is important to note that the same plant extract can be a therapeutic remedy at low concentrations, become an addictive drug at higher doses, and can potentially kill at high concentrations. Table 26.3 presents a few drugs, their plants of origin, and their medicinal applications.

Plant-based medicines are critical to health, but another challenge to their use is the availability and localization of the source. In many cases, as a medicine becomes widely used, supply limitations may lead to high costs and shortages, and any unforeseen issues, such as natural disasters, create challenges with availability. In most cases, scientists and pharmaceutical producers seek synthetic versions of the chemicals, and/or ways to mass produce them outside the normal process of plant growth. Chemist Percy Julian developed ways to mass produce numerous drugs, including methods to synthesize the glaucoma treatment physostigmine, mass produce progesterone from soybeans to prevent miscarriages, and inexpensively synthesize the widely used medicines cortisone and hydrocortisone. Efforts like these greatly increased both the access and consistency of medicines.