The Secondary Effects of Pencycuron on the Formation of Giant Protoplasts and the Lipid Peroxidation of Rhizoctonia solani AG4

The secondary effects of pencycuron on cell membrane of Rhizoctonia solani AG4 were investigated by the observation of giant protoplast formation and lipid per¬oxidaiton. Compared to protoplasts initially produced from the strains, protoplasts of R. solani R-C (sensitive strain) and Rh-131 (non-sensitive strain) increased in their size by 2.0-3.5 times 12 h after incubation in potato-dextrose broth containing novozyme (7 mg/ml) and β-glucuronidase (60 µl/ml) with 0.6 M mannitol (pH 5.2). The increase of protoplast size in R-C was slightly inhibited from 13.8 µm without pencycuron to 10.3 µm with 1.0 µg/ml of pencycuron. However, the size of giant protoplast of Rh-131 was not affected by the pencycuron treatment. Both strains R-C and Rh-131 did not exhibit the lipid peroxidation 12 h after the application of 1.0 µg/ml pencycuron. The remarkable peroxidation of membrane lipid was observed only in R-C 24 h after pencycuron application, but not in Rh¬131. Although the inhibition of giant protoplast forma¬tion and the membrane lipid peroxidation were observed only in the sensitive strain R-C by pencycuron, it is diffi¬cult to conclude that these are the primary mechanism of pencycuron. The mild activity of pencycuron on the inhibition of giant protoplast formation and late mem¬brane lipid peroxidation in the fungicide-sensitive strain did not coincide with the dramatic activity of pencycu¬ron in R. solani. Therefore, our results suggest that inhi¬bition of giant protoplast formation and membrane lipid peroxidation is the secondary effect of pencycuron. 

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