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1. Botany an epidermal pore, present in large numbers in plant leaves, that controls the passage of gases into and out of a plant
2. Zoology anatomy a mouth or mouthlike part
3. Surgery an artificial opening made in a tubular organ, esp the colon or ileum



a slitlike opening in the epidermis of aboveground organs of plants. The stoma is bordered by two guard cells, which are usually bean-shaped. The walls of the guard cells that face the stoma are thick, while the opposite walls are thin. The stoma leads to a large intercellular space, the substomatal cavity. The stoma is often surrounded by two or more cells that differ in shape from ordinary epidermal cells.

Stomata are found in the epidermis of all aboveground parts of the plant containing chlorophyll but are especially numerous in leaf epidermis (100–300 per sq mm). They regulate the exchange of gas and water vapor between the atmosphere and the cells of the plant by increasing and decreasing in width. Stomatal movement is effected by changes in the turgor of the guard cells. When turgor is increased, the thin parts of their walls stretch and are drawn away from the stoma. The walls that face the stoma are distended in the same direction, and the stoma opens. When the turgor of the guard cells decreases, the stoma closes. Change in the turgor of the guard cells occurs as a result of reversible conversion of starch, which is osmotically inactive, into osmotically active sugars. However, according to some data, potassium ions play an important, possibly leading, role in regulating the turgor of the guard cells. Scientists are currently investigating these data with the intention of formulating a new hypothesis of the mechanism of stomatal movement.

At night, the stomata of most plants are closed, and gas exchange and transpiration are minimal. During the day, when the weather is fair, the stomata are open. Carbon dioxide gas readily enters the internal tissues of the plant, and oxygen formed as a result of photosynthesis is released with water vapor into the atmosphere.



A small opening or pore in a surface.
One of the minute openings in the epidermis of higher plants which are regulated by guard cells and through which gases and water vapor are exchanged between internal spaces and the external atmosphere.
References in periodicals archive ?
When soil moisture becomes low, stomates will close to avoid excess water loss.
A similar situation occurs al Antifreeze Pond, with stomates and macrofossils indicating local spruce, but low (< 5%) pollen frequencies suggesting otherwise (Vermaire, 2005).
Turf density, percentage green turf cover, dollar spot diameter, stomate density, and trichome number and length were subject to ANOVA by location.
stomate (stomata)--Pores on the leaf surface that allow for gas exchange and permit loss of water in a process known as transpiration.
One of the ways that crops respond to water stress is to close their stomates, which results in reduced water evaporation (evapotranspiration) and increased temperature of the crop canopy.
Adults and nymphs are found on the undersides of leaves where they feed through the stomates on the contents of upper palisade parenchyma cells which results in stippling damage as well as reduced leaf photosynthesis (Buntin et al.
Blackbrush leaves are hypostomatic (Table 1), implying that stomates are located on the abaxial epidermis only.
On its surface, the specimen shows a number of fine streaks (FIGURE 5b), but nothing that could point either to some secondary branching off, to pores, stomates or other similar structures.
Stomates are present only on abaxial surface of the leaf.
1999), affirm that keeping plants in vitro produces physiological, structural, and anatomical abnormalities; such as absence of waxy cuticle, non functional stomates, photosynthetic inefficiency, and malfunctioning of hydric transport, these abnormalities resulting in elevated evapotranspiration rates.
Some suggest that when cytokinins are sprayed on plant leaves, the stomates will open wider and stay open longer, which leads to an increase in photosynthetic rates.