Plant hormone

Phytohormones ( Greek singular φυτοορμόνη, fitoormóni, " plant hormone " ) are biochemically acting plant's own (endogenous ) organic compounds that control and coordinate the growth and development of plants as primary messengers ( called signal molecules). Since they do not meet all the criteria of actual hormones, they can also be referred to as growth regulators. In addition to the real phytohormones there are numerous other secondary plant substances that also show growth-regulatory activity, for example, some phenolic compounds and steroids. However, these are by definition not to plant hormones.

Occurrence and detection

Phytohormones are found in all higher plants. Plant hormones are formed only in small amounts. The content of the various plant hormones depends on the plant organ and its state of development. Often, not to each other the absolute concentration is decisive, but the ratio of the phytohormones. Detection and determination of phytohormones effected by various sensitive bioassay method by physico-chemical methods and immunological analysis method. Significant levels of phytohormones can be found according to current knowledge, eg hops, red clover, soy beans, chick peas and yam.

Operation

Plant hormones are transported in the plant from the origination to a specific site of action, either from cell to cell (e.g. auxins ) of the conduction paths (for example, cytokinins ) or via the gas space between the cells ( ethylene ).

They are so to speak, the nervous system of the plant, by exchanging information between the plant tissues and cause to external environmental influences a specific reaction. Plant hormones regulate in close mutual interaction of the plant growth and development processes, and can trigger inhibit or promote this. They control and coordinate in this way the growth of root, shoot and leaf, the development of seeds and fruit, senescence and abscission, the apical dominance, breaks of plants, gravitropism and phototropism and many other processes.

Places of origin and based on the chemical interaction mechanism are still poorly understood. Site of action of the plant hormones are hormone- specific receptor proteins. Regulation of production: The plant hormones are either

• Irreversibly inactivated by various enzymatically controlled degradation reactions

Or

• Forms of memory transferred by conjugation with monosaccharides or amino acids in biologically inactive. These conjugates have as reversible (once activated ) deactivation products play an important role in the metabolism of the plant.

While phytohormones in vascular plants have a broad spectrum of activity ( the so-called pleiotropic effects ), very specific effects are described on the differentiation of Protonemas of mosses, especially auxins, cytokinins and abscisic acid. Education center and site of action are often not clearly separated.

Classification

Chemically phytohormones no single class of substances. ' Classical ' phytohormones are divided into five groups:

• The predominantly growth-promoting auxins, cytokinins and gibberellins,
• As well as the inhibitory phytohormone abscisic acid and ethylene.

In addition, brassinosteroids, jasmonates, salicylates and systemin play, the only peptide hormone a role. Polyamines do not count as phytohormones, since they do not only have a signaling function in the cell are always present, act as a direct reactant ( changed are shown in the reaction, irreversible) and at high concentrations ( mM ) are effective. Recently, the substance group of strigolactones is accepted as a phytohormone. These regulate ( or in conjunction with other phytohormones ), for example, the branching of the stem axis and arbuscular mycorrhizal hyphae as well as seed germination.

Application

• Plant hormones and effectively related growth regulators are widely used in agriculture, forestry and horticulture; see gibberellic acid.
• By fumigation with ethylene to speed up the ripening of immature fruits such as bananas, oranges and lemons in closed warehouses. Also it is used for induction of flowering in closed greenhouses. To speed up the ripening process of fruits already rich nanomolecular ethylene concentrations. Similarly, one can obtain by continuous removal of ethylene from storage facilities for fruits whose freshness.