In Situ Localization of Rapidly Accumulated Phenylalanine Ammonia-Lyase mRNA Around Penetration Sites of Phytophthora infestans in Potato Leaves. Beate Cuypers. Max-Planck-Institut für Züchtungsforschung, Abteilung Biochemie, D-5000 Cologne 30, West Germany. Elmon Schmelzer, and Klaus Hahlbrock. Max-Planck-Institut für Züchtungsforschung, Abteilung Biochemie, D-5000 Cologne 30, West Germany.. MPMI 1:157-160. Accepted 12 May 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988.

A combination of immunohistochemistry and in situ RNA-RNA hybridization enabled the localization of phenylalanine ammonia-lyase mRNA in young potato (Solanum tuberosum L. cv. Datura) leaf tissue infected with the late-blight fungus Phytophthora infestans. Within a few hours postinoculation, a marked increase in the mRNA concentration, relative to a low but detectable level in uninfected tissue, was observed in a halo of healthy-looking cells around fungal penetration sites. At this early stage of the infection process, fungal penetration sites already appeared as small local lesions caused by hypersensitive cell death. The response was more rapid in incompatible interactions than in compatible ones of a selected potato cultivar, carrying the P. infestans resistance gene R1, with appropriate races of the fungus.