The leaf alcohols cis-3-hexen-1-ol and trans-2-hexen-1-ol have been previou
sly shown to induce the wheat stem rust (Puccinia graminis f. sp. tritici)
to differentiate appressoria in a complex axenic culture medium. In this pa
per. the possible role of these chemicals in appressorium induction during
infection has been analysed further. The inductive potential of ethylene an
d three cutin monomers were also tested because they have been found to ind
uce appressoria in other fungi. Both hexenols were found to be inductive in
aqueous solution in the absence of media constituents. 0.5 1 mM trans-2-he
xen-1-ol Nas the most inductive resulting in a maximum of 51% appressorium
differentiation. trans-2-hexen-1-ol was also shown to be inductive in vapou
r form. In aqueous solution, trans-2-hexen-1-ol acted synergistically with
topographical signals by increasing the rate of appressorium induction. Com
bining the two signals also increased the total number of appresoria differ
entiated (88%). The other chemicals tested were noninductive although a bio
chemical domain rich in exposed cutin was localized around stomatal apertur
es of heat leaves. The characteristic bipolar morphology of appressoria for
med over stomata was found to be determined lj topographical signals. Overa
ll. Our data Support a role for both chemical signals (hexenols or their an
alogues) and topographical signals being involved in appressorium induction
by wheat stem rust. (C) 2001 Academic Press.