Excretory tissues are tissues that serve to remove metabolic waste from a plant [1] .
Excretory tissues are divided into secretory and excretory . In secretory tissues, metabolic wastes are stored inside individual cells, lactarias , lysigenic containers , and in excretory tissues they are secreted outward ( glandular hairs , nectaries ) or into the intercellular space ( schizogenic containers ) [1] .
Histology
Excretory structures do not have a specific localization in the plant , they are distributed more or less diffusely and have different origins: some of them are derivatives of protoderm ( exogenous structures), others are of the main meristem , vascular meristem ( cambium and procambium ) or permanent tissues, for example, phloem ( endogenous structures). The formation of secretory structures is ahead of the development of surrounding tissues [2] .
Secretory cells are somewhat reminiscent of meristem cells. They have thin walls, are interconnected by a few plasmodesmata , are rich in cytoplasm , contain large nuclei and leukoplasts . The degree of development of other organelles is determined by functional specialization [2] .
So, if carbohydrates are involved in the secretion (as in nectaries and mucus containers), then the Golgi apparatus is well developed in the cells and plastids are numerous. If the secret is terpenoid (as in ), then the cells have plastids and a plentiful smooth endoplasmic reticulum (EPR). Finally, if the secretion is protein (as in the glands of insectivorous plants ), then the cells are characterized by a well-developed rough ESR and Golgi apparatus. In the synthesis of the secretion of lactation, it is mainly involved in EPR [3] .
Exogenous Structures
The following is a brief description of the exogenous excretory structures of plants.
| Structure | Picture | Description | Plant examples |
|---|---|---|---|
| Hydatodes | Drip liquid water is extracted ( guttation ) at low transpiration and high soil moisture. In the simplest cases, they are unicellular or multicellular hairs that look similar to ordinary hiding hairs [3] . | Gonocarium , black pepper , multi-flowered beans , some ferns , rye , nasturtium , wild strawberries , buttercup , fuchsia , primrose , colocasia , currant , bird cherry [4] | |
| Glandular hairs | It is a structure of a single or multicellular pedicle and a more or less spherical head. The head cells produce essential oils that accumulate in the cuticle and, when enough oil is accumulated, tear it apart, going outside [5] . | Nettle , belladonna [5] , pelargonium | |
| Salt glands | They are found in plants growing on saline soils ( halophytes ), and an excess of salts is secreted. They are not associated with the conducting system , they are usually located in the recesses of leaves , sometimes protruding above their surface [5] . | Some representatives of the families of piggy , verbena , cereals [5] | |
| Hydropot | Characteristic for aquatic plants . Narrow stripes or rounded groups of cells located in the epidermis . The epidermis differs from other cells in smaller sizes, simpler form and better permeability. Rich in cytoplasm; serve both for absorption and for the removal of water [6] [7] . | Vodokras [8] | |
| Digestive glands | The structure varies [9] . | Carnivorous plants ( papaver , sundew , nepentes ) [9] | |
| Nectaries | Nectaries can be floral (that is, develop in flowers ) and extra- floral , formed on vegetative organs . Morphologically very diverse: from filamentous to disc-shaped. They are associated with conducting bundles , as the sugars secreted by nectaries come from the phloem . According to the structure, they occupy an intermediate position between the external glands and hydatodes [10] . | Many flowering plants, for example, viburnum , dogwood , privet , cherries , etc. |
Endogenous structures
The following table describes some types of endogenous excretory structures of plants.
| Structure | Picture | Description | Plant examples |
|---|---|---|---|
| Idioblasts | Single or grouped cells that differ from the surrounding cells in size, shape, content, etc. Oil , mucus , myrosin (contain the enzyme myrosin ) and crystalline cells (most often contain calcium oxalate ) are isolated depending on their contents [11] . | Oil cells - in representatives of the families of kirkazonovy , laurel , pepper ; mucous - cactus , malva , linden ; myrosin - cabbage , pepper , resed ; crystalline cells are very widespread [11] . | |
| Schizogenic receptacles (intercellular spaces) | They arise due to the destruction of the pectin layer connecting the cells. The schizogenic receptacles are [12] , as well as ether-oil and mucus passages . | Umbrella , aralia , conifers , cycas , ferns ; characteristic of the family of Hypericum [13] | |
| Lysogenic receptacles (intercellular spaces) | They arise due to the dissolution of a separate group of cells. As a result, a cavity is formed, filled with secretion, developed by the dissolved cells, the remnants of their membranes and protoplasts [13] . | Eucalyptus leaves, rue , citrus pericarp [13] | |
| Schizo-lysigenic receptacles (intercellular spaces) | Development begins schizogenously, then the size increases by lysis of the surrounding cells [14] . | Resin reservoirs in the secondary phloem of plants of the cypress family [14] | |
| Millers | Endogenous structures that secrete milky sap (latex) when a plant is damaged. They can be non-segmented (unicellular) or segmented , consisting of several tubular cells connected into single-row cords [15] . | Oleander , mulberry , euphorbia , dandelion and other Asteraceae , ficus , celandine , sanguinaria , poppy [16] |
Notes
- β 1 2 Lotova, Nilova, Rudko, 2007 , p. 21.
- β 1 2 Lotova, 2010 , p. 103.
- β 1 2 Lotova, 2010 , p. 105.
- β Lotova, 2010 , p. 105-106.
- β 1 2 3 4 Lotova, 2010 , p. 107.
- β Lotova, 2010 , p. 107-108.
- β Hydropots - article from the Dictionary of Botanical Terms
- β Lotova, 2010 , p. 296.
- β 1 2 Lotova, 2010 , p. 108-109.
- β Lotova, 2010 , p. 109-110.
- β 1 2 Lotova, 2010 , p. 110-111.
- β Lotova, 2010 , p. 111-112.
- β 1 2 3 Lotova, 2010 , p. 112.
- β 1 2 Lotova, 2010 , p. 112-113.
- β Lotova, 2010 , p. 113-114.
- β Lotova, 2010 , p. 113-115.
Literature
- Lotova L.I. Botany: Morphology and anatomy of higher plants. - Ed. 4th, additional .. - M .: Book House "LIBROCOM", 2010. - 512 p. - ISBN 978-5-397-01047-4 .
- Lotova L.I., Nilova M.V., Rudko A.I. Dictionary of phytoanatomical terms: a training manual. - M .: Publishing house LCI, 2007. - 112 p. - ISBN 978-5-382-00179-1 .