LACK OF CORRELATION BETWEEN TREHALOSE ACCUMULATION, CELL VIABILITY AND INTRACELLULAR ACIDIFICATION AS INDUCED BY VARIOUS STRESSES IN SACCHAROMYCES-CEREVISIAE

A pma1-1 mutant of Saccharomyces cerevisiae with reduced H+-ATPase act ivity and the isogenic wild-type strain accumulated high levels of tre halose in response to a temperature upshift to 40 degrees C and after addition of 10% ethanol, but only modest levels in response to a rapid drop in external ph and after addition of decanoic acid. There was, h owever, no correlation between the absolute levels of trehalose in the stressed cells and their viability. All these treatments induced a si gnificant decrease in intracellular ph, and surprisingly, this decreas e was very similar in both strains, indicating that intracellular acid ification could not be the triggering mechanism for trehalose accumula tion in response to stress, A careful investigation of metabolic param eters was carried out to explain how trehalose accumulated under the f our different stress conditions tested. No single and common mechanism for trehalose accumulation could be put forward and the transcription al activation of TPS1 was not unequivocally related to trehalose accum ulation. Another finding was that a pma1-1 mutant exhibited a two- to threefold greater capacity to accumulate trehalose than the isogenic w ild-type. This enhanced disaccharide synthesis could be attributed to a twofold higher trehalose-6-phosphate synthase activity, together wit h a fourfold higher content of intracellular UDP-Glc. In addition, thi s mutant showed 1.5-fold higher levels of ATP compared to the wild-typ e. The various stress treatments studied showed that a drop in intrace llular pH does not correlate with trehalose accumulation. It is sugges ted that plasma membrane alteration could be the physiological trigger inducing trehalose accumulation in yeast.