Plant hormones


Also found in: Dictionary, Thesaurus, Medical, Legal, Financial.
Related to Plant hormones: Plant growth regulators

Plant hormones

Organic compounds other than nutrients that regulate plant development and growth. Plant hormones, which are active in very low concentrations, are produced in certain parts of the plants and are usually transported to other parts where they elicit specific biochemical, physiological, or morphological responses. They are also active in tissues where they are produced. Each plant hormone evokes many different responses. Also, the effects of different hormones overlap and may be stimulatory or inhibitory. The commonly recognized classes of plant hormones are the auxins, gibberellins, cytokinins, abscisic acid, and ethylene. Circumstantial evidence suggests that flower initiation is controlled by hypothetical hormones called florigens, but these substances remain to be identified. A number of natural or synthetic substances such as brassin, morphactin, and other growth regulators not considered to be hormones nevertheless influence plant growth and development. Each hormone performs its specific functions; however, nearly all of the measurable responses of plants to heredity or environment are controlled by interaction between two or more hormones. Such interactions may occur at various levels, including the synthesis of hormones, hormone receptors, and second messengers, as well as at the level of ultimate hormone action. Furthermore, hormonal interactions may be cooperative, antagonistic, or in balance.

The term plant growth regulator is usually used to denote a synthetic plant hormone, but most of the synthetic compounds with structures similar to those of the natural hormones have also been called hormones. For instance, the synthetic cytokinin kinetin is considered a hormone. See Abscission

There are a number of applications of plant hormones in agriculture, horticulture, and biotechnology. Synthetic auxins are used as weed killers. Auxins are also used to counteract the effects of hormones that promote the dropping of fruit from trees. Gibberellins are used extensively to increase the size of seedless grapes: when applied at the appropriate time and with the proper concentration, gibberellins cause fruits to elongate so that they are less tightly packed and less susceptible to fungal infections. Gibberellins are also used by some breweries to increase the rate of malting because they enhance starch digestion. They have also been sprayed on fruits and leaves of navel orange trees to prevent several rind disorders that appear during storage. They are used commercially to increase sugarcane growth and sugar yields. Cytokinins and auxins are used in plant cell culture, particularly in cultivating genetically engineered plants. The ability of cytokinins to retard senescence also applies to certain cut flowers and fresh vegetables. Ethylene has been used widely in promoting pineapple flowering; flowering occurs more rapidly and mature fruits appear uniformly, so that a one-harvest mechanical operation is possible. Because carbon dioxide in high concentrations inhibits ethylene production, it is often used to prevent overripening of picked fruits. Ethylene is also used for accelerating fruit ripening. See Hormone, Plant growth, Plant physiology

References in periodicals archive ?
The effect of plant hormones on cell cycle progression has been studied in various monocots and dicots (see Table 3) and it was found that linker histone H1 phosphorylation plays a significant role in this response.
The earliest recorded observation leading to the discovery of plant hormones is that of Charles Darwin.
Two other plant hormones, auxin and gibberelic acid, remained unchanged throughout berry development.
discuss each of the six classes of plant hormones, the history involved in their discovery, and their effect on specific physiological processes.
Gibberellins are a group of thirty or more closely related plant hormones that promote cell enlargement, often causing dramatic increases in plant height.
And ,partly as a result of the BSE scare, more people are eating soya, as a meat substitute, that contains female plant hormones.
Several plant hormones also have a significant effect on pigmentation during the postharvest period, especially ethylene and cytokinins.
The study did not draw conclusions from the survey findings, saying the high levels of vitellogenin could have resulted from sources other than endocrine disrupters, such as female sex hormones from humans and livestock, or plant hormones from animal feed.
An opportunity to dissect genetically the interactions between plant hormones in the regulation of plant growth and plant water relations under water deficits is lost in the classification of hormone-deficient and -insensitive mutants of Arabidopsis in terms of the relatively obscure phenotypes of "drought escape", "drought tolerance", and "drought rhizogenesis".
A team of University of Missouri plant physiologists has discovered how key plant hormones help plants deal with drought.
Other reported CCC uses include the separation of agricultural chemicals and plant hormones, antibiotics, drug metabolites, dyes, fatty acids, glycosides, lipids, and flavinoids.