Section 6
Chapter 5,248

Effect of inhibitors of melanin biosynthesis on appressorial penetration and reductive reactions in pyricularia oryzae and pyricularia grisea

Chida, T.; Sisler, H.D.

Pesticide Biochemistry and Physiology 29(3): 244-251


ISSN/ISBN: 0048-3575
DOI: 10.1016/0048-3575(87)90154-4
Accession: 005247012

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Appressorial penetration of onion epidermal walls by wild-type strains P-2 and O-42 of Pyricularia oryzae was more sensitive to fthalide (4,5,6,7-tetrachlorophthalide) than penetration by wild-type strain 4091-5-8 and black mutant strain BL-3 of Pyricularia grisea. Cerulenin completely blocked appressorial penetration of P. oryzae strain P-2 or P. grisea strain BL-3, but penetration capacity of these appressoria could be largely restored when 0.1 mM scytalone. Fthalide and tricyclazole inhibited the conversion of 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN) to 1,3,8-trihydroxynaphthalene (1,3,8-THN) and 1,8-dihydroxynaphthalene (1,8-DHN) as well as the conversion of scytalone to 1,8-DHN by cell-free extracts of P. oryzae or P. grisea. These inhibitors blocked the NADPH-dependent reductase reactions involved in the conversion of 1,3,6,8-THN to scytalone and the conversion of 1,3,8-THN to vermelone in the melanin biosynthetic pathway to 1,8-DHN. The two reductase reactions in extracts from P. oryzae P-2 were about 10 times as sensitive to fthalide or tricyclazole as those in extracts of P. grisea. Reductase activity with either 1,3,6,8-THN or 1,3,8-THN as substrates was present in only trace amounts in cell-free extracts of the buff mutant, P. oryzae P-2 m-1.

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