ISHS Acta Horticulturae 394: Plant Bioregulators in Horticulture
GROWTH RETARDANTS: BIOCHEMICAL FEATURES AND APPLICATIONS IN HORTICULTURE |
| Author: | W. Rademacher |
| Keywords: | Plant growth retardants, Gibberellin biosynthesis, Side effects, Applications in horticulture |
| Abstract:
Most plant growth retardants inhibit the formation of growth-active gibberellins (GAs) and can, thus, be used to reduce unwanted shoot elongation. To date, three different types of chemicals with such an effect have become known: Quaternary ammonium compounds (e.g. chlormequat chloride and mepiquat chloride) inhibit the conversion of geranylgeranyl-pyrophosphate to ent-kaurene. The following steps leading to ent-kaurenoic acid are catalyzed by monooxygenases which are cytochrome P450-dependent. Compounds with an N-containing heterocycle (e.g. anycmidol, flurprimidol, paclobutrazol and uniconazole) inhibit these enzymes. Later stages of GA metabolism involve dioxygenases which require 2-oxoglutarate as a co-substrate. Acylcylcohexanediones, such as trinexapac-ethyl or prohexadione-Ca, are structural mimics of 2-oxoglutarate and can, thus, block these reactions. Evidence is available that daminozide has a similar mode of action. Under certain conditions, side effects on related enzymatic reactions can be observed. This may affect - positively or negatively - the usefulness of a given compound in a distinct indication. Actual horticultural uses of plant growth retardants include the reduction of vegetative growth in fruit trees, grapes and other woody plant species, the regulation of turf growth and height reduction in ornamentals. In addition to morphoregulation an improved resistance against different types of climatic stress can often be observed. Acylcyclo-hexanediones, which are currently introduced into the market, appear to offer advanced solutions for some indications. | |
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