Fig. 6. The role of actin cables in Spitzenkörper integrity and polarised growth. Unbudded yeast cells expressing Mlc1-YFP were induced to form hyphae, stained with Concanavalin A (Con A) conjugated to either Alexa 488 or Texas Red and treated with 10 µm Cytochalasin A (CA) and as described in the flow chart. The protocol results in the formation of young germ tubes in which the cell walls fluoresce green. Cell walls formed after CA treatment are not stained with Con A-A488 (green) but are stained with Con A-TR (red). (A-C) A CA-treated hypha. (D-F) An untreated control hypha. CA treatment results in swollen tips that are stained red but not green. Thus, the swelling arises from new isotropic growth, not from swelling of a pre-existing hyphal tip. Mlc1-YFP, which is also visible in the green channel, disappears from the tip of CA-treated cells, but remains in the typical Spitzenkörper organisation in untreated cells (D, arrow; F, inset). An Mlc1 cytokinetic ring persists in the CA-treated cells (arrow in C). The response of hyphal germ tubes to CA treatment was uniform in the culture and the images shown are typical. Bar, 5 µm.