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a compound produced by plants in small quantities to stimulate growth or formation. Phytohormones are diverse in structure and effect. They include auxins, gibberellins, kinins, and florigen, the composite hormonal agent that promotes flowering. Phytohormones regulate many life processes of plants, including germination, growth, the differentiation of tissues and organs, flowering, and the ripening of fruits.

Phytohormones are usually formed in one organ and transported to another organ or a different part of the same organ. In contrast to animals, plants do not have special organs for the synthesis of hormones. Certain organs are more highly saturated with particular hormones than others. Thus, the apical meristem of the stem is richer in auxins, while the leaves are richer in gibberellins and florigen, and the roots and maturing seeds are richer in kinins. Phytohormones produce a great variety of effects. Auxins, for example, can stimulate the dilation of cell walls and also cell division. Phytohormones act in a definite order, with kinins and gibberellins predominating in the early stages of development and auxins in later stages. They interact closely with one another; for example, a change in the concentration of one phytohormone influences the reaction caused by another. Natural growth inhibitors, such as abscisic acid, constitute a special group of phytohormones.

The effects of phytohormones on growth may be rapid, in which case the membrane system is involved; the phytohormones take part in processes that influence the structure of the plasma membrane. When the effects are slow, nucleic acids and proteins are involved.


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References in periodicals archive ?
In summary, suppressed GA pathway and phytohormone imbalance may be the major causes for dwarfing of the D plants.
Phytohormones are the regulatory molecules produced by plants in very low concentration.
In summary, the bacteria-associated plant growth properties shown in our experiments suggested that PGPR bacteria were able to produce phytohormone auxin (IAA) that stimulated the growth of maize and wheat crops.
Table 2: Effects of different phytohormone combinations on adventitious shoots induction and proliferation of red pitaya primary explants
Similarly, the media containing various phytohormone combinations were used for induction of shoot organogenesis for J.
The importance of preconditioning at high carbohydrate concentrations, after the increased concentration of carbohydrates in plant tissues promoted by the use of sucrose in combination with phytohormones, has been demonstrated (BHARDWAJ; MISHRA, 2005; STENVALL et al.
Phytohormone control of the tobacco anionic peroxidase promoter.
The elongation effects in mangroves has been attributed to phytohormone like gibberellins in Rhizophora mangle (Smith et al.
This is much more potent than the well known gaseous phytohormone, ethylene (Falkenstein et al.
The color maintenance of the epidermis should be related to the lower biosynthesis and ethylene action in MA (JAYAS; JEYAMKONDAN, 2002), because the color change during the ripening of plums is a process dependent on the action of this phytohormone (ARGENTA et al.
In the current study, endophytic bacteria were isolated from the four varieties of the aerobically grown rice and these isolates were studied for their ability in producing phytohormone like IAA, GA and cytokinin.