Endocytosis and vacuolar morphology in Saccharomyces cerevisiae are altered in response to ethanol stress or heat shock

The vital lipophilic dye N-(3-triethylammoniumpropyl)-4-[6-(4-(diethylamino )phenyl]hexatrienyl) pyridinium dibromide (FM 4-64) was used to study the e ffect of ethanol stress and heat shock on endocytosis in the yeast Saccharo myces cerevisiae. Yeast cells stained with FM 4-64 were placed in a culture chamber and the internalization of the dye was monitored by fluorescence m icroscopy during perfusion of the cells with fresh growth medium. In the ab sence of ethanol in the perfusion medium, the internalization of FM 4-64 fr om the plasma membrane to the vacuolar membrane by yeast cells harvested fr om the exponential phase of growth was completed in 30 min. The presence of 6% (v/v) ethanol in the perfusion medium had no obvious effect on the inte rnalization of FM 4-64 from the plasma membrane, but did lead to an accumul ation of the dye in endocytic intermediates. Consequently, vacuolar membran e staining was delayed. Cells stained with FM 4-64 and subjected to heat sh ock displayed a similar effect, with endocytic intermediates becoming more prominent with the severity of the heat shock. For both ethanol stress and heat shock, vacuolar morphology altered from segregated structures to a sin gle, large organelle. The findings of this study reinforce previous observa tions that ethanol stress and heat shock induce similar responses in yeast. Copyright (C) 1999 John Wiley & Sons, Ltd.