CUTICULAR AND NON-CUTICULAR SUBSTRATE INFLUENCE ON EXPRESSION OF CUTICLE-DEGRADING ENZYMES FROM CONIDIA OF AN ENTOMOPATHOGENIC FUNGUS, NOMURAEA-RILEYI

Larval cuticle from Trichoplusia ni, Helicoverpa (= Heliothis) zea, and Heliothis virescens and a cellulose substrate were used to quantify release of proteolytic, chitinolytic, and lipolytic enzymes by germinating conidia of the entomopathogenic fungus, Nomuraea rileyi. There was no significant difference in conidial viability incubated with T. ni, H. zea or cellulose substrates. Conidial viability on H. virescens cuticle, however, was significantly lower (ca. 19-25%) than the other three substrates. The presence of cuticle substrates, especially cuticle of T. ni, stimulated germination. The nature of the substrate influenced both the time and quantity of the enzymes expressed. Specific proteases (aminopeptidase, chymoelastase, trypsin) generally were expressed earlier and/or in greater quantities on cuticular than on the cellulose substrate. Although both chitinolytic enzymes (endochitinase, N-acetylglucosaminidase) were detected on all three cuticular substrates, their activity was substantially lower than that of the proteolytic enzymes. Lipase activity was only minimally present. Early concurrent release of both proteases and chitinases suggested that both may be important in the penetration of the larval integument by germinating conidia of N. rileyi. Expression of proteases and chitinases, especially aminopeptidase and endochitinase was probably a specific response to cuticle, because little or no activity was expressed on the non-host, cellulose substrate.