5 Things of Stomata – Closing & Opening, Structure, Types, and Functions

What is Stomata?

Stomata are tiny openings in the epidermis of leaves such as Digitalis, Senna, and others, or in young green stems such as Ephedra, in flowers such as clove, and in fruit such as fennel and orange peel. Guard cells are a pair of kidney-shaped cells that surround these apertures.

Structure of Stomata

The stomatal configuration, which consists of a slit-like opening and guard cells, is commonly referred to as a’stoma.’ Neighboring cells, also known as subsidiary cells, are epidermal cells that surround the guard cells. These resemble the other epidermal cells in many cases, such as in Digitalis, although they differ in size, organisation, and shape in a wide variety of plants.

Types of Stomata (stomatal arrangement):

The epidermal cells surrounding the stomata have been divided into four groups based on their arrangement:

Diacytic or Caryophyllaceous (cross celled):

The stoma is accompanied by two subsidiary cells, each with a long axis that is perpendicular to the stoma’s. This stoma is also known as the Labiatae type since it is found in numerous plants belonging to the Labiatae family, including vasaka, tulsi, spearmint, and peppermint.

Anisocytic or Cruciferous (unequal celled):

The stoma is normally surrounded by three subsidiary cells, one of which is significantly smaller than the others. This form of stoma is also known as the Solanaceous type because it is found in numerous plants in the Solanaceae family, including Belladonna, Datura, Hyoscyamus, Stramonium, and Tobacco, as well as several plants in the Compositae family.

Anomocytic or Ranunculaceous (irregular celled):

The stoma is surrounded by a variety of cells that are similar to epidermal cells in Digitalis, eucalyptus, henna, lobelia, neem, and other plants.

Paracytic or Rubiaceous (parallel celled):

In Senna and many Rubiaceous plants, the stoma is frequently surrounded by two subsidiary cells with long axes parallel to the stoma.

Actinocytic (radiate celled):

As in Uva ursi, the stoma is encircled by a circle of radiating cells.

Closing and Opening of Stomata

The presence of sugar and starch in the guard cells affects the process of closing and opening the stomata.

Two guard cells surround the stomata, which control their opening and closing. During the day, stomata open to allow gas exchange and to release water vapor through transpiration. The change in turgor pressure of the guard cell causes the stomata to open and close.

Water is absorbed by the roots during the day due to increased transpiration pull, and it is transferred to various regions of the plant via the xylem. The guard cell swells and becomes turgid after receiving this water. As a result, the stomatal pore becomes open.

The guard cell becomes floppy and shrinks as the roots absorb less water at night. Stomatal pores close as a result of this.

Read: Extraction- Types, Methods, and Applications

Functions and Distributions of Stomata

In the plant body, stomata are responsible for gaseous exchange and transpiration.

The lower epidermis of a dorsiventral leaf has the most of them, whereas the top epidermis has the least. Stomata are restricted to the upper epidermis only in isobilateral leaves, and there are no stomata in submerged leaves.

Stomata are only present on the lower surface of Buchu and Neem, whereas stomata are present on both surfaces of Belladonna, Datura, Senna, and other plants.

Stoma distribution varies greatly between the upper and lower epidermis. Stomata are found in grooves or pits in the stem or leaf of desert plants and those with xerophytic characteristics, such as Ephedra, Agave, Oleander, and others.

Because the stomata immersed in pits are protected from wind gusts, this is a unique adaptation for reducing excessive evaporation.