Secretory structures

Secretory structures (plant)

Cells or organizations of cells which produce a variety of secretions. The secreted substance may remain deposited within the secretory cell itself or may be excreted, that is, released from the cell. Substances may be excreted to the surface of the plant or into intercellular cavities or canals. Some of the many substances contained in the secretions are not further utilized by the plant (resins, rubber, tannins, and various crystals), while others take part in the functions of the plant (enzymes and hormones). Secretory structures range from single cells scattered among other kinds of cells to complex structures involving many cells; the latter are often called glands.

Epidermal hairs of many plants are secretory or glandular. Such hairs commonly have a head composed of one or more secretory cells borne on a stalk. The hair of a stinging needle is bulbous below and extends into a long, fine process above. If one touches the hair, its tip breaks off, the sharp edge penetrates the skin, and the poisonous secretion is released.

Glands secreting a sugary liquid—the nectar—in flowers pollinated by insects are called nectaries. Nectaries may occur on the floral stalk or on any floral organ: sepal, petal, stamen, or ovary.

The hydathode structures discharge water—a phenomenon called guttation—through openings in margins or tips of leaves. The water flows through the xylem to its endings in the leaf and then through the intercellular spaces of the hydathode tissue toward the openings in the epidermis. Strictly speaking, such hydathodes are not glands because they are passive with regard to the flow of water.

Some carnivorous plants have glands that produce secretions capable of digesting insects and small animals. These glands occur on leaf parts modified as insect-trapping structures. In the sundews (Drosera) the traps bear stalked glands, called tentacles. When an insect lights on the leaf, the tentacles bend down and cover the victim with a mucilaginous secretion, the enzymes of which digest the insect. See Insectivorous plants, Venus' flytrap

Resin ducts are canals lined with secretory cells that release resins into the canal. Resin ducts are common in gymnosperms and occur in various tissues of roots, stems, leaves, and reproductive structures.

Gum ducts are similar to resin ducts and may contain resins, oils, and gums. Usually, the term gum duct is used with reference to the dicotyledons, although gum ducts also may occur in the gymnosperms.

Oil ducts are intercellular canals whose secretory cells produce oils or similar substances. Such ducts may be seen, for example, in various parts of the plant of the carrot family (Umbelliferae).

Laticifers are cells or systems of cells containing latex, a milky or clear, colored or colorless liquid. Latex occurs under pressure and exudes from the plant when the latter is cut.

References in periodicals archive ?
A diversity of secretory structures is involved in the production of different compounds from secondary metabolism, documented in a number of Euphorbiaceae species (Metcalfe and Chalk 1950).
The structural similarity of colleters with other types of secretory structures led researchers to confuse them with extrafloral nectaries and resin glands (Martins et al.
However, glandular trichomes and EFNs are distinct secretory structures (EVERT, 2013).
Morphoanatomy and development of leaf secretory structures in Passiflora amethystina Mikan (Passifloraceae).
Depending on the taxonomic group under study, the essential oil can be found in various secretory structures such as glandular trichomes, cavities, ducts and oil cells.
Thus, this paper aims to provide information about the secretory structures and their contents located in the leaf, flower, root and rhizome of A.
These trichomes, whether isolated or in groups, are often secretory structures such as nectaries, oil producing or salt excreting glands (Fahn 1979).
Starch has been found to serve as the predominant energy reserve in other well-studied secretory structures (Fahn 1979, Paiva & Machado 2008), and the juxtaposition of mitochondria and amyloplasts indicate the energy need for starch hydrolysis, as discussed by Paiva & Machado (2008).
These tested exercises include instructions for preparing microscope slides and sectioning and staining plant material and chapters on complex tissues, secretory structures, reproductive organs, and related topics.
Plant gums, resins, and essential oils are often produced in large quantities by specialized secretory structures.
He provided a brief historical overview of theories concerning the development of secretory structures, and he proposed a classification scheme that was based on gland development.
Abstract: The genus Hymenaea is characterized by a great diversity of secretory structures, but there are no reports of colleters yet.