FIG. 4.

Disoriented FSM extension and defective spore formation in septin mutant cells. (A) Strains JB60 (h⁻ spn5Δ) and JB61 (h⁺ spn5Δ) were grown overnight in YE medium at 30°C, mixed in equal numbers on an MM-N plate, incubated for 3 days at 25°C, collected, fixed with methanol and acetone, stained with bisbenzimide (see Materials and Methods), and visualized by DIC (left) and by DIC plus fluorescence (right). h⁻ and h⁺ wild-type strains were handled identically and are shown for comparison. Arrows, immature or defective spores with poorly defined coats and apparently without enclosed nuclei. (B) Strains THP18 (wild type) and TK144 (spn5Δ) harboring pAL(spo3-GFP) were sporulated, fixed, and examined by fluorescence microscopy. (C) Strain TK144 harboring plasmid pREP81(GFP-psy1) was grown on an EMM plate, transferred to an SSA plate, and incubated for 13 h before the beginning of time-lapse observations (see Materials and Methods). Times are indicated in minutes since the beginning of observation. Arrows, FSMs showing disoriented extension.