Effect of Mepanipyrim on Uptake of Various Substrates and Macromolecular Biosyntheses in <i>Botrytis cinerea</i>

Abstract

Mepanipyrim, N-(4-methyl-6-prop-l-ynylpyrimidin-2-yl)aniline, hardly inhibited the mycelial respiration and the syntheses of DNA, RNA, protein, lipids and cell walls in mycelia of Botrytis cineyea at 100 eg/ml. By the treatment of mepanipyrim at 10-100 g/ml, each uptake of 14C-labeled glucose, acetate, uridine, thymidine, alanine or glucosamine by the mycelia of B. cineyea was inhibited, but no apparent uptake inhibition of these precursors was observed below 1, csg/ml. The inhibition by mepanipyrim of the active transport process across the cellular membrane may bring about a chronic deficiency in most intracellular substrates essential for growth and development. However, the effect of mepanipyrim appeared not to be strong enough to disrupt the overall functions of cell membrane in B. cineyea; because it neither stimulated the leakage of protein, phosphate, glucose and electrolytes from the cells, nor influenced the bursting rate of protoplasts by osmotic shock.

Biochemical basis of selective disease controlling activity of mepanipyrim

“…Since mepanipyrim inhibits the uptake of growth substrates such as amino acids and glucose by B. cinerea, 3) the next attempt examined the uptake of these substrates to demonstrate whether uptake inhibition is related with the difference of mycelial inhibitory activity among these pathogens.…”

“…It also has good disease control activity against the Alternaria alternata apple pathotype (leaf spot) and the powdery mildew genera Erysiphe and Podosphaera. 1,2) Mepanipyrim inhibits the uptake of growth substrates such as amino acids and glucose by B. cinerea at an effective dose of 10-100 mg/ml 3) and blocks the secretion of host-cell walldegrading enzymes at 1 mg/ml. The inhibition of protein secretion is the mode of action considered the most important mechanism in disease control.…”

“…4) While mepanipyrim markedly affects the infection process of B. cinerea at 1-10 mg/ml, especially germ tube elongation, secondary appressorium formation and penetration, it hardly inhibited spore germination and did not fully inhibit the mycelial growth of B. cinerea. 1,3) Taking advantage of its strong inhibition against germ tube elongation instead of weakly mycelial growth inhibition, the FGA-paper disc method 5) can evaluate the sensitivity of B. cinerea to mepanipyrim. In addition, assay qualities of the FGA-paper disc method were improved to use gelatin in the medium, resulting in utilizing the inhibitory activity of mepanipyrim in protease secretion.…”

“…Mepanipyrim, however, strongly affects fungal diseases caused by B. cinerea despite the weak inhibition of spore germination and mycelial growth in vitro. 1,3) The in vitro antifungal activity of mepanipyrim thus does not accurately reflect disease control efficacy in vivo.…”

Effect of culture age on mepanipyrim-mediated inhibition of pectinase secretion in Botrytis cinerea

“…7,8) Mepanipyrim also did not affect spore germination and it did not fully inhibit mycelial growth despite its strong inhibition of germ tube elongation. In our previous study, 9) mepanipyrim was assumed to generally retard the development and growth of B. cinerea rather than to kill or to fully inhibit it. For example, secondary appressoria formation of B. cinerea was delayed by 48-120 hr after incubation in the presence of 1-10 mg/ml mepanipyrim.…”