Fig. 6. Modulation of the microtubule cytoskeleton in response to osmotic stress. GFP–-tubulin was expressed by the atb2.nmt81GFP allele in the indicated strains at 30°C. Osmotic stress was applied by the addition of sorbitol in filter-sterilized EMM2 to a final concentration of 1.2 M. (A) Each panel shows, from left to right, a 20-second-interval series of maximal projections of untreated wild-type cells (upper panels) or cells filmed immediately after being subjected to osmotic stress (lower panels, see also supplementary material Movie 1). (B) Each panel shows, from top left to bottom right, a 3-minute-interval series of maximal projections of wild-type cells. Sorbitol was added immediately after the second (3 minute) time point (arrow). In the image boxed in red (the 36-minute time point, top right), the microtubule bundles have fragmented into a number of short microtubules occurring at a variety of angles to the long axis of the cell. Later panels show that the microtubule cytoskeleton then gradually recovers its pre-stress distribution (see also supplementary material Movie 2). (C,D) Each panel shows a maximal projection of either sty1. cells (C) or wis1.DD cells (D) taken immediately before treatment (0 sec.; left panels) or 100 seconds after treatment with pre-warmed media (control; right panels) or with pre-warmed media containing 2.4 M sorbitol (sorbitol; lower right panels) (see also supplementary material Movies 3 and 4).