MadSci Network: Botany |
Many plants temporarily store starch in their chloroplasts. Students often test leaves for starch. Starch is a polymer of glucose. About 15% of flowering plant species do not store carbohydrates as starch. Wheat, barley, onion, Jersusalem artichoke and other species make fructans instead of starch. Fructans are polymers of fructose and are stored in the cell vacuole. In plants that store mainly sucrose, such as sugar cane, the sucrose is also found in the vacuole. Seeds store starch or other carbohydrates, proteins and/or oils. These nutrients are intended to nourish the developing seedling. Starch is stored in plastids termed amyloplasts. Oil storage plastids are termed elaioplasts. Protein storage plastids are termed proteinoplasts or proteoplasts. For some photos of plastids, search Visuals Unlimited. In angiosperms, the seed nutrients may be stored in the triploid (3n) endosperm, as in corn, wheat and rice; in the cotyledons of the embryo, as in bean and peanut, or in both endosperm and cotylelons. In gymnosperm seeds, such as, pine and spruce, the nutrients are in the cotyledons and the haploid (1n) female gametophyte. Seeds are the most important source of human food because of their carbohydrate, protein and oil content. Corn, wheat and rice are the world's most important crops. Corn is found in thousands of processed foods often as high fructose corn syrup or corn starch. Almost all cooking oils are obtained from seeds. Examples of cooking oils include soybean oil, corn oil, canola oil, cottonseed oil, coconut oil, peanut oil, safflower oil, sunflower oil and sesame seed oil. Many plants have specialized underground storage stems such as corms (crocus, gladiolus), tubers (potato) and rhizomes (ginger and iris). Sugarcane stores large amounts of sucrose in its aboveground stems. Many plants have roots specialized for storage, such as carrot, beet and sweet potato. Sugar beets store large amounts of sucrose in their storage roots. Bulbs store nutrients in fleshy leaves. Familiar bulbs are onion, garlic, lily, tulip, daffodil, hyacinth and amaryllis. Fruits are not really areas of nutrient storage for the plant because the plant or its offspring cannot use the stored nutrients. Nutrients stored in fruits are designed to attract animals to eat the fruit and thereby disperse the seeds. References Testing a leaf for Starch Basic Fructan Info Modified Roots, Stems and Leaves A Zillion Uses for Corn
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