Control of fungal plant disease using inhibitors of polyamine biosynthesis

West, Helen (1989) Control of fungal plant disease using inhibitors of polyamine biosynthesis. PhD thesis, University of Glasgow.

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Abstract

The effects of a number of inhibitors of polyamine biosynthesis on the growth of two species of biotrophic fungi, five species of necrotrophic fungi and one hemibiotroph were studied. The fungi used were: 1. Erysiphe qraminis DC. ex Merat f.sp. hordei Marchal 2. Ustilago maydis (DC.) Corda 3. Pythium ultimum Trow 4. Septoria nodorum (Berk.) Berk, apud and Br. 5. Pyrenophora teres Drechsler 5. Gaeumannomyces qraminis (Sacc.) v. Arx and Olivier f.sp. tritici Walker 7. Fusarium culmorum (W.G.Sm.) Sacc. 8. Phytophthora infestans (Montague) de Bary. The work carried out involved the following inhibitors: 1. 2-difluoromethylornithine (DFMO) 2. (E)-2-(fluoromethyl) dehydroornithine (Delta-MFM) 3. (E)-2-(fluoromethyl) dehydroornithine methyl ester (Delta-MFMO.Me) 4. (2R, 5R)-6-heptyne-2, 5-diamine (RR-MAP) 5. 2-hydrazinoornithine 6. 2-difluoromethylarginine (DFMA) 7. Methylglyoxal-bis (guanylhydrazone) (MGBG) 8. Cyclohexylamine (CHA) Compounds 1-5 are inhibitors of ornithine decarboxylase, 6 inhibits arginine decarboxylase, 7 is an inhibitor of S-adenosylmethionine decarboxylase and 8 inhibits spermidine synthase. The effects of each of these inhibitors on infection of barley leaves by mildew were examined. Leaves of barley cv. Golden Promise were sprayed with various concentrations of the inhibitors as post-inoculation treatments. DFMO, MGBG and a combination of the two were also applied as pre-inoculation treatments. All of the inhibitors significantly reduced mildew infection. With the exception of the DFMA treatments, post-inoculation sprays were more effective than pre-inoculation ones. When DFMO, MGBG and DFMA were sprayed onto leaves at different time intervals, DFMO and MGBG most effectively controlled mildew when sprayed on the third day after inoculation. DFMA was more efficient as a pre-inoculation treatment. Addition of polyamines to DFMO sprays increased mildew infection compared to that resulting from the DFMO treatment alone, although infection was less than in the control. Whereas pre-inoculation sprays of putrescine and spermidine resulted in an increase in mildew infection by the final day of measuring, the post-inoculation treatments of polyamines reduced mildew growth. Several of the inhibitors (1-4 and 5-8) were used to examine their effects on growth of the remaining fungi in vitro. This was achieved by supplementing growth media with the inhibitors and also with polyamines, both alone and in combination with DFMO. Species-dependent responses to the inhibitors were observed and although growth of some fungi (notably G. graminis) was reduced by various inhibitors, some increases in growth were noted after treatment. This was possibly a result of secondary enzyme production or overproduction of the target enzyme, leading to an initial surge of polyamine synthesis and enhanced growth. The effects of DFMO were reversed by the addition of polyamines to the growth medium. Once it had been established that the inhibitors did have an effect on fungal growth, an attempt was made to understand the processes involved in uptake of polyamines, precursors and DFMO by the fungi. F. culmorum and G. graminis were selected for this work because of their different responses to the inhibitors. Uptake of the polyamines, ornithine and arginine appeared to be biphasic, with one system operating at low substrate concentrations and another at high substrate concentrations. DFMO was taken up linearly and was non-saturable over the concentrations studied. Uptake of the amino acids and polyamines by F. culmorum was pH dependent and competition work suggests that putrescine, spermidine and ornithine have different uptake systems. However, uptake of DFMO was inhibited in the presence of putrescine, spermidine and ornithine suggesting that its uptake may not be limited to one uptake system. The reduction in uptake of putrescine and DFMO by F. culmorum when sodium azide (a respiratory inhibitor) was added suggests a partial energy requirement. This was not the case for spermidine uptake. The fungi, when grown in the presence of DFMO did not generally show enhanced uptake of polyamines as may have been expected, perhaps because the inhibitor can be rendered relatively ineffective in long term studies by intracellular decarboxylation. Exposure to MGBG, however, resulted in a decrease in uptake, possibly due to mitochondrial damage or non-specific effects of this inhibitor. Cations present within the growth and assay media affected uptake of polyamines by both F. culmorum and G. graminis, with magnesium ions causing the greatest inhibitory effects.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: D R Walters
Keywords: Plant pathology
Date of Award: 1989
Depositing User: Enlighten Team
Unique ID: glathesis:1989-72299
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 24 May 2019 15:12
Last Modified: 24 May 2019 15:12
URI: http://theses.gla.ac.uk/id/eprint/72299

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