Extracellular Glycoprotein(s) Associated with Cellular Differentiation in Magnaporthe grisea. Jin-zhong Xiao. The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan. Akihisa Ohshima, Takashi Kamakura, Tadayuki Ishiyama, and Isamu Yamaguchi. The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan. MPMI 7:639-644. Accepted 25 May 1994. Copyright 1994 The American Phytopathological Society.

uring the infection process of Magnaporthe grisea on rice plants, the conidinl germ tube differentiates info a specific infection structure, an appressorium, for penetration into the host. Formation of appressoria was observed not only on plant leaves of various species including hosts and nonhosts, but also on synthetic solid.substrata. We reported that the hardness of the solid surface contacted by conidial germ tubes was an important parameter for differentiation (Xiao et al. 1994). Possible cellular factors involved in sensing solid surfaces and signal transduction during these early stages in pathogencsis were investigated. When germinated on a synthetic substratum, germ lubes and appressoria adhered firmly to the contact surface. Scanning electron microscopy showed abundant mucilaginous substances around germ tubes and appressoria. Conidial adhesion and appressorium formation were significantly inhibited by protease, (-mannosidase and a- glucosidase, but not by (-glucosidase, ß-galactosidasc, lipase, and chitinase. The mucilage disappeared when germinated in the presence of protease, (-mannosidase, and ß-glucosidase. Concanavalin A, a lectin binding to (-D-ninnnosc and (-D-glucose, specifically suppressed appressorium formation at concentrations higher than 10 (g/ml, but did not significantly affect conidial germination and adhesion. Mucilaginous materials were also observed around germ tubes and appressoria on various plant leaves. These data suggest that extracellular glycopro-tein(s) bind germ tubes and appressoria to a contact surface, and at least a part of those glycoprotein(s) are further involved in sensing and transmission of information about the inductive parameters for cellular differentiation. The same mechanisms are probably involved in pathogencsis in vivo.