Idioblast
Idioblasts are cells or cell groups scattered in a plant tissue , which differ in their structure and their tasks from the surrounding cells.
The term idioblast goes back to Julius Steiner (1844–1918), who (1874) described them as “cells that differ significantly from their neighborhood in their size, structure or content in an otherwise uniform tissue”. The word idioblast is derived from ἰδιότης (idiótes) "private person", "peculiarity", "peculiarity" (see: idiot ) and blastem (Greek "germ", "scion"). You can therefore also see them as “weirdos” in the cell structure. In "Strasburger" it is stated that the "richer the tissue structure of an organism, the higher the degree of differentiation achieved by it or the division of labor of its cell associations". The number of cell types and tissue types is a measure of the organizational level of an organism. These "weirdos" occur both in the plant tissue of the parenchyma and in the closure tissue ( epithelium ) and, more rarely, in vascular bundles . A few examples will now be given:
Idioblasts in closing tissue (epidermis)
Idioblasts stored in plant epidermis are mostly hair cells or gland cells, sometimes a combination of both, like the stinging hairs of the nettle . A particularly important task have the stoma cells of stomata for gas exchange of plants.
Idioblasts in basic tissue (parenchyma)
Many plants have so-called excretory idioblasts in the base tissue, especially in the palisade parenchyma and in the sponge parenchyma of the leaves. These often produce special phytochemicals such as essential oils , resins, alkaloids , tannins , but also mucus or milk juices (in the case of milkweed plants ). The cells form these substances by means of the endoplasmic reticulum (ER) and the Golgi apparatus and thus fill the vacuoles until they completely fill the cells. Examples are the oil cells in the avocado fruits , in the roots of the ginger , in the bark of the cinnamon tree and in many rutacea ( citrus ). The excretion of calcium oxalate , which forms surprisingly large crystal bundles in crystal idioblasts (raphids), is very widespread in leaves .
The star hair cells ( astrosklereids ) have a combination of cube-shaped salt excretions combined with strongly thickened cell walls and a star-shaped hair shape, some of which protrude bizarre into the air tissue ( aerenchyma ) of water lily leaves . Spurge plants , oleanders and rubber trees have undivided milk tubes as a special feature , for which many typical secretion cells merge at an early stage in their development. These multinucleated, branched tubes then grow through the entire parenchyma as giant cells. Such tubes then serve as storage for milk juice and can be several meters long. They belong to the largest cells of all.
Meaning of idioblasts
The idioblasts allow adaptations to various ecological conditions. Hair cells and stoma cells, for example, enable the control of water evaporation. The wax glands in the epidermis, which form the cuticle of leaves, serve the same purpose. Hydathodes that release water serve the same purpose by actively releasing water from wetland plants ( hygrophytes ).
Excretion : Plants on salty soils (e.g. the samphire on sea coasts) are able to excrete excess minerals through salt glands and thus control the osmotic pressure osmosis in the tissues.
Other cell types serve primarily to protect against herbivorous insects or vertebrates, because many secretions are either toxic ( calcium oxalate , alkaloids ) or taste bitter ( tannins ). Some of these secretions also have an anti-fungal and / or antibacterial effect.
The heavily hardened sclereids (stone cells) and the star cells (astrosklereids) must also be seen under this aspect of protection against eating. Leaking latex or resin can quickly seal injuries to tissues. Another function is to attract animals with essential oils or other fragrances for the purpose of sexual reproduction. Nectaries with sugary secretions serve as a reward for useful insects. On the other hand, such attractants can also contribute to the supply of minerals in "carnivorous plants" (for example sundew (Drosera)).
Unresolved issues
Since idioblasts are mostly scattered as single cells in uniform tissue, it also means that they must arise from or with these cells through inequitable (unequal) divisions. This inevitably raises the question of their ontogeny or gene regulation , because they obviously have a building metabolism that differs from that of the surrounding cells. Although individual cells, the idioblasts do not lie randomly in the tissue, but rather form a certain repetitive arrangement. This raises the question of how to coordinate their creation. See the article on the ontogeny of the stomata ( stoma (botany) ).
Applications
Probably since the beginning of human cultural history people have known about the special ingredients of plants and have also been using them for thousands of years for drugs, medicine and various sorcery. "Many higher plants collect extractable organic substances in sufficient quantities that are economically interesting enough to be able to serve as chemical starting material for various scientific or technical applications." The economically important plants serve the industry as a source for oils, tannins, saponins , natural Rubber , waxes , pharmaceuticals and many other special products. "
Of the 25 best-selling pharmaceutical products worldwide, 12 are derived from natural products. Assuming how widespread the secretory and excretory idioblasts are in plants, it is astonishing how few have been investigated for biologically active substances so far. Balandrin estimates that no more than 15% of the 250,000-750,000 known species of higher plants were examined for special ingredients. The chances are therefore "good to excellent that many plant ingredients with potentially useful biological or technological properties have not yet been discovered and thus unused."
Idioblasts in microscopic analysis
If substances from parts of plants z. If, for example, there is a broken leaf, these substances can often be easily identified microscopically or checked for quality and purity. Imported green tea , for example, is identified and checked by looking for the heavily branched, thick-walled Astrosklereids in the older leaves of Camellia sienensis . For the purposes of customs and drug searches ( criminalistics ), plant products are checked for hemp content ( Cannabis sativa ) by microscopically looking for so-called retort hair, which is attached to a cystolite (stone) made of calcium carbonate (CaCO 3 (limestone)) at the base. are provided.
See also
literature
- Julius Sachs : textbook of botany. 4th edition. Leipzig 1874.
- G. Wanner: Microscopic-Botanical Internship. Thieme, Stuttgart 2004, ISBN 3-13-440312-9 , p. 68f, p. 98f.
- P. Sitte et al .: Strasburger textbook of botany . 34th edition. Heidelberg 1999, ISBN 3-8274-0779-6 , pp. 117, 123, 172.
- Liselotte Langhammer: Illustrated atlas for the microscopic analysis of herbal medicinal drugs. de Gruyter, 1986, ISBN 3-11-010210-2 .
- JA Klocke, ES Wurtele, WH Bollinger: Natural plant chemicals: sources of industrial and medicinal materials MF Balandrin. In: Science. Vol. 228, No. 4704. American Association for the Advancement of Science 1985, pp. 1154-1160.
- Friedl Weber: Negative Idioblasts . Ferdinand Berger & Söhne GmbH, Horn, Austria 1958. [1] (PDF; 649 kB)
Web links
- Representation of different plant cell types and plant tissues
- Detailed description
- Microscopic analysis of plant parts and ingredients (PDF; 419 kB)