Phytohormone
Phytohormones are the plants' own ( endogenous ) organic compounds which, as primary messenger substances (so-called signal molecules), control and coordinate the growth and development of plants . In addition to the real phytohormones, there are numerous other phytochemicals that also have a growth-regulating effect, for example some phenolic compounds and steroids . However, by definition, these do not belong to the plant hormones.
Research history
The discovery of hormone-like substances in plants was a result of studies of phototropism in oat coleoptiles . The coleoptile is a shell that surrounds the cotyledon in grasses such as oats . Charles Darwin and his son Francis Darwin described in 1880 that when the growing coleoptile bends in the direction of laterally incident light, the coleoptile tip “perceives” the light stimulus and in the stretching zone further below (cf. stretching growth ) the curvature towards the light occurs. How the stimulus, which at that time was still imagined as analogous to a psychological sensation, is passed on from the tip to the extension zone, remained unclear for a long time. The influential botanist Wilhelm Pfeffer took the view that this happens via an interaction between the cells of the coleoptile. It was not until 1913 that Peter Boysen-Jensen initiated an experimental investigation of this question by showing that inserting a mica plate on the shadow side of the coleoptile prevents the curvature, while a mica plate on the light side has no effect. In 1927, Frits Warmolt Went provided the final proof that it was a matter of diffusion by placing coleoptile tips on agar plates and using these to apply the diffusing substance to capped coleoptiles. Frits AFC Went and Fritz Kögl introduced the term “phytohormone” in 1933.
Mode of action
The plant hormones are transported in the plant from the point of origin to a specific place of action, either from cell to cell (e.g. auxins ), via the conduction pathways (e.g. cytokinins ), or via the gas space between the cells ( ethylene ). Plant hormones regulate the plant's growth and development processes in close mutual interaction and can trigger, inhibit or promote them. In this way, they control and coordinate the growth of roots , shoots and leaves , the development of seeds and fruit , senescence and abscission , apical dominance , rest periods of plants, gravitropism and phototropism and many other processes.
Places of origin and the mechanism based on chemical interaction have not yet been researched very well. The target of the phytohormones are hormone-specific receptor proteins . Regulation of production: the plant hormones are either
- irreversibly inactivated by various enzymatically controlled degradation reactions,
or
- converted into biologically inactive storage forms through conjugate formation with monosaccharides or amino acids . As reversible (reactivatable) deactivation products, these conjugates have an important function in the metabolism of the plant.
While phytohormones have a broad spectrum of activity in vascular plants (the so-called pleiotropic effect), very specific effects on the differentiation of the protonema of the moss have been described , especially for auxins, cytokinins and abscisic acid . The place of education and the place of work are often not clearly separated from each other.
Classification
Chemically, phytohormones are not a uniform class of substances. 'Classic' phytohormones are divided into five groups:
- the predominantly growth-promoting auxins, cytokinins and gibberellins ,
- as well as the inhibitory phytohormones abscisic acid and ethylene.
Also play brassinosteroids , jasmonats , salicylates and systemin, the only peptide hormone, a role. Polyamines are not phytohormones because they do not only have a signaling function, are always present in the cell, act as direct reaction partners (emerge from the reaction in a changed manner, irreversibly) and are effective in high concentrations (mM). The group of substances called strigolactones has recently been accepted as a phytohormone. These regulate (also in interaction with other phytohormones) z. B. the branching from the stem axis and hyphae of arbuscular mycorrhizal fungi and the germination of seeds .
application
- Plant hormones and related growth regulators are widely used in agriculture, forestry and horticulture .
- By fumigation with ethylene to ripening unripe fruits such as accelerated bananas , oranges and lemons in closed warehouses. It is also used to induce flower formation in closed greenhouses. Nanomolecular ethylene concentrations are sufficient to accelerate the ripening process of fruits. Conversely, by continually removing ethylene from fruit warehouses, fruit can be kept fresh.
See also
literature
- Heide Theiß, Bruno Hügel: Experiments on the developmental biology of plants - phytohormones. Quelle & Meyer, Wiesbaden 1995, ISBN 3-494-01242-3 .
Web links
- Peter von Sengbusch: Phytohormones (plant hormones) and other growth regulators (2004)
- Phytohormones: The signal generators of the plant kingdom (article on Pflanzenforschung.de)
Individual evidence
- ↑ Ilse Jahn (Ed.): History of Biology . 3rd edition, Nikol special edition, Hamburg 2004, p. 522f.
- ^ Eva L. Decker, Wolfgang Frank, Eric Sarnighausen, Ralf Reski : Moss systems biology en route: Phytohormones in Physcomitrella development . In: Plant Biology. 8, 2006, pp. 397-406. doi: 10.1055 / s-2006-923952 .
- ↑ X. Xie, K. Yoneyama, K. Yoneyama: The Strigolactone Story . In: Annual Review of Phytopathology . tape 48 , April 2010, p. 93-117 , doi : 10.1146 / annurev-phyto-073009-114453 , PMID 20687831 .
- ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 2: Cm-G. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1981, ISBN 3-440-04512-9 , pp. 1203-1205.