Inhibition of Gibberellin Production in the Fungi Gibberella fujikuroi and Sphaceloma manihoticola by Plant Growth Retardants

Abstract

The effect of different types of plant growth retardants on fungal gibberellin (GA) formation has been studied in cultures of Gibberella fujikuroi and Sphaceloma manihoticola. Quaternary ammonium compounds (chlormequat chloride, mepiquat chloride, Amo-1618), triazoles (uniconazole and several experimental compounds), and the norbornanodiazetine tetcyclacis inhibited GA biosynthesis in both fungal species. Concentrations between 2 x 1iO`and 10-M were required for a 50% inhibition of the production of gibberellin A3 in Gibberella fujikuroi and of giberellin A4 in Sphaceloma manihoticola. The formation of other prominent GAs was affected at a similar degree of intensity. Tetcyclacis was the most active compound in both fungi. Compared to the growth retardants mentioned above, the biological activity of chlorphonium chloride was low. The acylcyclohexanediones prohexadione and LAB 198 999 had virtually no activity. Most likely, this lack of activity is due to a rapid metabolism of the compounds in the cultures. For the triazole-type compounds and tetcyclacis, a relatively distinct correlation exists in their ability to inhibit GA formation in fungal cultures, to block ent-kaurene oxygenase in a cell-free system, and to reduce shoot growth of rice seedlings. Due to differences in their metabolic fate and species specificities, such conclusions cannot be made for the other compounds.Plant growth retardants play an important role in agriculture and horticulture in reducing unwanted shoot elongation (21). At present, five major groups have been recognized. Ethylene-releasing compounds such as ethephon reduce shoot elongation mainly by inhibiting cell division. Daminozide most likely acts by causing a more rapid inactivation of GAs1 and by inhibiting GA translocation (31). Quaternary ammonium and phosphonium compounds (e.g. CCC, mepiquat chloride, Amo-1618, and chlorphonium chloride), compounds with a nitrogen-containing heterocycle (e.g. ancymidol, tetcyclacis, paclobutrazol, uniconazole, and inabenfide), and acylcyclohexanediones (e.g. prohexadione, cimectacarb, and LAB 198 999) inhibit the biosynthesis of GAs. It is known that representatives of the latter three groups block, respectively, the cyclization of geranylgeranyl pyrophosphate via copalyl pyrophosphate into ent-kaurene, the oxidative reactions from ent-kaurene to ent-kaurenoic acid, or 3,B-hydrox-

In vitro and in vivo evidence for the inhibition of brassinosteroid synthesis by propiconazole through interference with side chain hydroxylation

“…4 Additionally, the application of chemicals that targeting GA biosynthesis represents a feasible way to control the unwanted longitudinal shoot growth of crops. 5 Paclobutrazol (Pac) 6 and uniconazole (Ucz) 7 are widely used plant growth regulators (their structures are shown in Fig. 1).…”

“…Both compounds inhibit GA biosynthesis thereby reducing plant height and inducing the morphological characteristics of GA deficient mutants. [6][7][8] Recent progress on the studies of brassinosteroid (BR) functions has indicated that BRs is a good target for bioengineering of high yield of crops. 9 Analysis the BR-deficient mutants gave evidences that BRs play a key role in promoting plant growth.…”

Reducing peat and growth regulator input in camellia pot cultivation

“…Th e most used and eff ective type of control, however, is the one that involves the application of chemical growth retardants. Several plant growth regulators labelled for use in fl oriculture, such as the triazoles and pyrimidines, were developed to reduce stem elongation by inhibiting the synthesis of gibberellins (Rademacher 1989(Rademacher , 1992Brown et al 1997). A secondary eff ect linked to the inhibition of gibberellic acid biosynthesis is, for some plant genus including Camellia, an early and enhanced fl owering (Halevy 1983).…”

Gibberellin biosynthesis inGibberella

“…The number of gibberellin genes available from plants has increased notably in the past few years (reviewed in Avalos eta/., 1997). The enzymes of the gibberellin pathway should be similar in plants and fungi, as suggested by sensitivity to the same inhibitors (Graebe, 1987;Rademacher, 1992). The identification of conserved domains in the kaurene synthase genes of various plants made possible the cloning of their counterpart in the fungus Phaeosphaeria (Kawaide et a/., 1997).…”