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.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
It was possible to verify the presence of secretory structures, of the secretory cavity type, with large rounded cavity delimited by secretory cells and with cells that project to the epidermis.
This difference in plant material sensitivity to drying temperature among species can be attributed to secretory structures and their location in plants, as well as to chemical composition of the essential oil (ARGYROPOULOS & MULLER, 2014).
Individual cells or parts of the secretory structures were first identified as a region of interest (shortly ROI) and marked by rings or rectangles.
This finding is the opposite pattern from that found in most gonochoric gobioid species, in which sperm duct-associated secretory structures have been described only in association with the male reproductive system.
Colleters are secretory structures characterized by elongated central axis formed by fundamental parenchyma, surrounded by an epidermal palisade layer (DA CUNHA & VIEIRA 1993/97).
From these researches, we could see that alkaloids of leaves are mainly distributed in epidermis (protective tissue), parenchyma, and secretory structures. In our studies, the alkaloids of leaves of Thymus quinquecostatus could be observed in the glandular trichomes.
These trichomes, whether isolated or in groups, are often secretory structures such as nectaries, oil producing or salt excreting glands (Fahn 1979).
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. These include glandular trichomes, secretory cavities, and secretory ducts.
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).