Spindle birefringence of isolated mitotic apparatus analysed by pressure treatment

Sea-urchin zygote mitotic apparatus (MA) isolated in a glycerol/dimethylsulphoxide medium were treated with pressure. Pressure treatment had no effect on spindle birefringence when MA were in full-strength isolation medium. After placing MA in quarter-strength isolation medium, pressures of 4-0 X 10(3)-1-8 X 10(4) lbf in.-2 (2 X 76 X 10(4)-I X 24 X 10(5) k N m-2) for 15 min caused reduction of birefringence which occurred in 2 steps: firstly 20-30% of the birefringence was lost, and then, at higher pressures, the rest of the birefringence was lost. Electron microscopy suggested that pressure-induced changes were in non-microtubule material. Pressure treatment had no effect on MA isolated with hexylene glycol when the MA were pressurized in hexylene glycol; but pressure treatment did cause loss of birefringence when MA isolated in hexylene glycol were transferred immediately into glycerol/dimethylsulphoxide medium and were subsequently treated with pressure (after dilution into quarter-strength glycerol/dimethyl-sulphoxide). We discuss the differences in response between isolated MA and in vivo MA, and we discuss the possibility that 2 components contribute to MA birefringence.