Mode of Action of Copper 8-Quinolinolate on Alternaria kikuchiana

Abstract

Spore germination, hyphal elongation and hyphal penetration of Alternaria kikuchiana were observed on alcohol-treated epidermal strips of onion bulb. I₅₀ of copper sulfate, 8-quinolinol and copper 8-quinolinolate on germination of A. kikuchiana were 10^-3M, 10^-4M and 10^-6M respectively, and those on penetration were 3×10^-4M, 3×10^-5M and 10^-6M respectively, indicating that copper ion and 8-quinolinol acted synergistically against A. kikuchiana. The synergism was more remarkable when 8-quinolinol existed more than twice the concentration of copper ion. On the contrary, the synergism was less remarkable when copper ion existed more than a half the concentration of 8-quinolinol. 8-Quinolinol at 10^-2M accelerated state 4 respiration of rat liver mitochondria to 2.5 times and showed uncoupling effect on oxidative phosphorylation at higher than 10^-3M. 8-Quinolinol also accelerated respiration of the mitochondrial fraction of A. kikuchiana to 1.4 times at 2×10^-3M. Thus a possibility was, suggested that the inhibitory effect of 8-quinolinol on the growth of A. kikuchiana is related to the uncoupling effect. Since mitochondrial membrane is generally permeable to uncouplers, the fungal cell membrane which is similar to mitochondrial membrane by nature may also be permeable to 8-quinolinol and permit copper ion to pass the barrier along with 8-quinolinol as a complex to afford the synergistic fungicidal action of the both chemicals. Further, there is a possibility that 8-quinolinol makes it possible for copper ion to pass through mitochondrial innerr membrane of A. kikuchiana and inhibit not only 6-phosphogluconate dehydrogenase in extramitochondrial cytoplasm, but also many dehydrogenases in mitochondria.