IDENTIFICATION OF THIGMORESPONSIVE LOCI FOR CELL-DIFFERENTIATION IN UROMYCES GERMLINGS

The sites along Uromyces appendiculatus germ tubes that are responsive to topographical induction for appressorium formation were determined using glass micropipettes. The germ tubes were perturbed with the micropipettes at different sites and durations. The most responsive region of the germ tubes for appressorium formation was within 0-10 mu m from the cell apex where >90% of the perturbed germ tubes developed appressoria. Furthermore, only the cell surface in contact with the substratum was responsive. Appressoria could not be induced to form, under any conditions, by perturbing cell-substratum regions of the germ tubes more than 40 mu m from the apex. Maximum appressorium formation occurred when the perturbing micropipette was left in place for >20 min.