auxins



auxins defined in 1951 year

auxins - auxins;
auxins - Group of plant hormones, produced by regions of active cell division and enlargement, e.g. growing tips of stems and roots, that regulate many aspects of plant growth. Promote growth by increasing rate of cell elongation, including curvature responses of organs to stimuli ofgeotropism and phototropism, and by cell division, e.g. initiation of cambium activity in association with cytokinins, adventitious root formation in cuttings; cause dominance of certain parts of plant over others, e.g. inhibition of lateral bud development by apical bud; involved in flower initiation, sex determination, fruit growth; delay leaf fall and fruit drop. Actively transported in polar (basipetal) manner in young tissues.

Auxins occurring naturally in plants include indole-3-acetic acid (IAA) and indole-3-acetonitrile (IAN). IAA has been isolated from such diverse sources as corn endosperm, fungi, bacteria, human saliva and, the richest natural source, human urine. In addition to naturally occurring auxins many substances with plant growth regulation effects, the so-called synthetic auxins, have been made in the laboratory. Some of these are now used on a very large scale for regulating some growth processes of agriculturally and horti-culturally important plants, e.g. inhibition of sprouting of potato tubers, thus lengthening period for which they can be stored, prevention of fruit drop in orchards, synchronous flowering (and thus fruiting) in pineapple, parthenocarpic fruit production, e.g. in tomato, avoiding disadvantage of poor pollination. At increased though still relatively low concentration auxins inhibit growth and death may result. Some of the synthetic auxins have differential toxicity towards different plants (toxicity of 2, 4-dichlorophenoxy-acetic acid to dicotyledonous and non-toxicity to monocotyledo-nous plants is best example) and this has been exploited very successfully in the control of weeds in cereal crops and lawns. See also: Hormone.

near auxins in Knolik


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