Plant hormones

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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

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Regarding gibberellins, this plant hormone influences germination, seedling growth, stem elongation, leaf development, bud outgrowth, flower induction, and xylem expansion (Gabriele et al., 2010; Ikezaki et al., 2010; Mauriat et al., 2011; Nadeau et al., 2011; Zhao et al., 2011; Taiz & Zeiger, 2013).
This might be due to the use of plant hormones that may modify or have an effect on the synthesis of bioactive compounds of G.
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.
Plant hormones, on the other hand, tend to be very general, and each kind of hormone may perform many different functions.
"This research is the first step in unraveling the role of several plant hormones in ripening," Davies said.
There are six classes of plant hormones: auxins, gibberellins, cytokinins, abscisic acid, ethylene, and brassinosteroids.
Stoller's Crop Health Therapy products increase crop quality and yield by balancing plant hormones throughout the growth cycle, so the plant can better withstand stress caused by unfavorable weather and pests.
These plant hormones, which travel from the roots to the rest of the plant, are regulators of aging.
Edamame is also notable for its health-promoting plant hormones, called isoflavones.
Isoflavones are a group of non-steroidal plant hormones (phyteoestrogens) that have a similar structure to human oestradiol.
Phytoestrogens: Scientists have begun to study the benefits of a group of plant hormones known as phytoestrogens.