Bioregulatory Effects of the Fungicidal Strobilurin Kresoxim-methyl in Wheat ( Triticum aestivum )
✍ Scribed by Grossmann, Klaus; Retzlaff, Günter
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 385 KB
- Volume
- 50
- Category
- Article
- ISSN
- 1526-498X
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✦ Synopsis
Apart from its fungicidal e †ect, the strobilurin kresoxim-methyl (BAS 490 F) was found to induce physiological and developmental alterations in wheat (T riticum aestivum L.) which are seen in connection with improved yield. In a series of biotests including heterotrophic maize and photoautotrophic algal cell suspensions, duckweed, isolated mustard shoots and germinating cress seeds, kresoxim-methyl showed a similar response pattern to standard auxins (e.g. indol-3-ylacetic acid, IAA ; 2-(1-naphthyl)acetic acid, a-NAA). Auxin-like activity of kresoxim-methyl was also found when stem explants of tobacco were cultured on a hormone-free medium. Kresoxim-methyl stimulated shoot formation, particularly at 10~7 M. The same e †ect was induced by 10~8 M IAA. The determination of phytohormone-like substances in shoots of wheat plants foliar-treated with 7 ] 10~4 M kresoxim-methyl revealed only slightly changed levels of endogenous IAA, gibberellins and abscisic acid. In contrast, the contents of dihydrozeatin riboside-type cytokinins increased to 160% of the control, while transzeatin riboside-and isopentenyladenosine-type cytokinins remained nearly unchanged. The most remarkable alterations were the reductions in 1aminocyclopropane-1-carboxylic acid (ACC) levels and ethylene formation which were demonstrated in intact plants, leaf discs and the shoots of wheat subjected to drought stress. Kresoxim-methyl a †ected the induction of ACC synthase activity which converts S-adenosyl-methionine to ACC in ethylene biosynthesis. In shoots from foliar-treated wheat plants, 10~4 M kresoxim-methyl inhibited stress-induced increases in endogenous ACC synthase activity, ACC levels and ethylene formation by approximately 50%. Reductions in ACC synthase activity and ACC levels of 30% were also obtained at low concentrations of a-NAA (10~6 M). In contrast, ACC synthase activity in vitro was not inÑuenced by adding the compounds. In wheat leaf discs, the inhibiting e †ect of kresoximmethyl, a-NAA and IAA on ethylene formation was accompanied by delayed leaf senescence, characterized by reduced chlorophyll loss. However, in contrast to kresoxim-methyl which showed only inhibitory activity on ethylene synthesis over a wide range of concentrations applied, the auxins stimulated ethylene production at high concentrations of about 10~4 M. The inhibition of ethylene biosynthesis by kresoxim-methyl, together with an increase in endogenous cytokinins could explain the retardation of senescence and the intensiÐed green leaf pigmentation in wheat exposed to this strobilurin.