RESUMO
An increase of the unsaturation level of the cellular fatty acids was observed at sublethal or superoptimal temperatures in Saccharomyces cerevisiae. The hypothesis of this paper is that a high unsaturated fatty acids relative content "per se" is not a prerequisite for withstanding sublethal temperature stress in yeast but is the result of oxygen-consuming desaturase activation, with consequent reduction of oxygen and the oxygen free radicals as they form during thermal stress. In the thermotolerant strains, no increase of cellular thiobarbituric acid reactive substances (TBARSs) was observed when temperature approached the maximal growth temperature, suggesting prevention of oxidative damage. On the other hand, the values of TBARSs tripled at 42 degrees C in nonthermotolerant strains. When a sublethal hydrogen peroxide treatment preceded a rapid temperature rise, a selected thermotolerant strain responded with a relative increase of saturated fatty acids. This response, associated with an insignificant viability loss due to the double stress, suggests the induction an alternative oxygen consumption mechanism preventing excessive fatty acid unsaturation, which could be detrimental to the cells in the presence of hydrogen peroxide at sublethal temperatures.
