Gland (botany)
Encyclopedia
In plant
s, a gland is defined functionally as a plant structure which secretes one or more products. This may be located on or near the plant surface and secrete externally, or be internal to the plant and secrete into a canal or reservoir. Examples include glandular hairs, nectaries, hydathode
s, and the resin canals in Pinus
.
s such as Acanthus
, Aegiceras
, Aegialitis
, and Avicennia
are a distinctive multicellular trichome
, a glandular hair found on the upper leaf surface and much more densely in the abaxial indumentum. On the upper leaf surface they are sunken in shallow pits, and on the lower surface they occur scattered among long nonglandular hairs composed of three or four cells. Development of the glands resembles that of the nonglandular hairs until the three-celled stage, when the short middle stalk cell appears. The salt gland continues to develop to produce two to four vacuolated cells at the level of the epidermis, the stalk cell with an almost completely cutinized wall, and at least eight terminal cells. The terminal cells have a thin, perforated cuticle which separates from the cell walls apically, leaving an enclosed cavity between them. The secreted salt evaporates and forms visible crystals.
s of the female plant. After flower formation begins, some of the glands, especially on bracts near the flowers, develop stalks projecting them outward from the plant surface. The glands consist of a layer of disk cells, whose outer surface splits to create a large secretory cavity lined by cell wall and cuticle components. Together the disk cells and secretory cavity form a round head atop the narrow stalk. These cavities come to contain large amounts of cannabidiol
in hemp
-producing strains, or tetrahydrocannabinol
and cannabinol
in marijuana
-producing strains. These compounds appear to be produced beginning in specialized plastid
s called lipoplasts. These produce spheres of oily secretions, including terpene
s, which pass through the cell membrane and wall to accumulate as vesicles in the secretory cavity. Final reaction to cannabinoids appears to occur outside the disk cell cyctoplasm. The glands gradually darken as they mature, with loss of cannabinoids over time (perhaps to evaporation) and eventually undergo abscission
from the plant.
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s, a gland is defined functionally as a plant structure which secretes one or more products. This may be located on or near the plant surface and secrete externally, or be internal to the plant and secrete into a canal or reservoir. Examples include glandular hairs, nectaries, hydathode
Hydathode
A hydathode is a type of secretory tissue in leaves, usually of Angiosperms, that secretes water through pores in the epidermis or margin of leaves, typically at the tip of a marginal tooth or serration. They probably evolved from modified stomata...
s, and the resin canals in Pinus
Pine
Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...
.
Salt glands of the mangrove
The salt glands of mangroveMangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
s such as Acanthus
Acanthus
Acanthus , in its feminine form acantha , is the Latinised form of the ancient Greek word acanthos or akanthos, referring to the Acanthus plant. It can also be used as the prefix acantho-, meaning "thorny"...
, Aegiceras
Aegiceras
Aegiceras is a genus of trees and shrubs from Southeast Asia, Malesia, Australia and the Pacific Islands. They occur in coastal or estuarine areas.-Species:* Aegiceras corniculatum* Aegiceras ferreum* Aegiceras floridum...
, Aegialitis
Aegialitis
Aegialitis is a genus of two shrubby mangrove species, with one native to Southeast Asia and the other native to Australia and Papua New Guinea.- Description :...
, and Avicennia
Avicennia
Avicennia is a genus of flowering plants currently placed in the bear's breeches family, Acanthaceae. It contains mangrove trees, which occur in the intertidal zones of estuarine areas and are characterized by aerial roots. Species of Avicennia occur worldwide south of the Tropic of Cancer.The...
are a distinctive multicellular trichome
Trichome
Trichomes are fine outgrowths or appendages on plants and certain protists. These are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae.- Algal trichomes :...
, a glandular hair found on the upper leaf surface and much more densely in the abaxial indumentum. On the upper leaf surface they are sunken in shallow pits, and on the lower surface they occur scattered among long nonglandular hairs composed of three or four cells. Development of the glands resembles that of the nonglandular hairs until the three-celled stage, when the short middle stalk cell appears. The salt gland continues to develop to produce two to four vacuolated cells at the level of the epidermis, the stalk cell with an almost completely cutinized wall, and at least eight terminal cells. The terminal cells have a thin, perforated cuticle which separates from the cell walls apically, leaving an enclosed cavity between them. The secreted salt evaporates and forms visible crystals.
Cannabinoid-secreting glands of hemp
Cannabis plants are broadly covered with sessile glands, and other hairs throughout above-ground portions of the plant. There is a particularly high concentration of glands on the bractBract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often different from foliage leaves. They may be smaller, larger, or of a different color, shape, or texture...
s of the female plant. After flower formation begins, some of the glands, especially on bracts near the flowers, develop stalks projecting them outward from the plant surface. The glands consist of a layer of disk cells, whose outer surface splits to create a large secretory cavity lined by cell wall and cuticle components. Together the disk cells and secretory cavity form a round head atop the narrow stalk. These cavities come to contain large amounts of cannabidiol
Cannabidiol
Cannabidiol is a cannabinoid found in Cannabis. It is a major constituent of the plant, representing up to 40% in its extracts.It has displayed sedative effects in animal tests...
in hemp
Hemp
Hemp is mostly used as a name for low tetrahydrocannabinol strains of the plant Cannabis sativa, of fiber and/or oilseed varieties. In modern times, hemp has been used for industrial purposes including paper, textiles, biodegradable plastics, construction, health food and fuel with modest...
-producing strains, or tetrahydrocannabinol
Tetrahydrocannabinol
Tetrahydrocannabinol , also known as delta-9-tetrahydrocannabinol , Δ1-THC , or dronabinol, is the main chemical psychoactive substance found in the cannabis plant. It was first isolated in 1964. In pure form, it is a glassy solid when cold, and becomes viscous and sticky if warmed...
and cannabinol
Cannabinol
Cannabinol is a psychoactive substance cannabinoid found in Cannabis sativa and Cannabis indica/afghanica. It is also a metabolite of tetrahydrocannabinol . CBN acts as a weak agonist of the CB1 and CB2 receptors, with lower affinity in comparison to THC.- External links :* Compounds found in...
in marijuana
Cannabis (drug)
Cannabis, also known as marijuana among many other names, refers to any number of preparations of the Cannabis plant intended for use as a psychoactive drug or for medicinal purposes. The English term marijuana comes from the Mexican Spanish word marihuana...
-producing strains. These compounds appear to be produced beginning in specialized plastid
Plastid
Plastids are major organelles found in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell...
s called lipoplasts. These produce spheres of oily secretions, including terpene
Terpene
Terpenes are a large and diverse class of organic compounds, produced by a variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium. They are often strong smelling and thus may have had a protective...
s, which pass through the cell membrane and wall to accumulate as vesicles in the secretory cavity. Final reaction to cannabinoids appears to occur outside the disk cell cyctoplasm. The glands gradually darken as they mature, with loss of cannabinoids over time (perhaps to evaporation) and eventually undergo abscission
Abscission
Abscission is a term used in several areas of biology. In plant sciences it most commonly refers to the process by which a plant drops one or more of its parts, such as a leaf, fruit, flower or seed...
from the plant.