INDUCTION OF HEAT, FREEZING AND SALT TOLERANCE BY HEAT AND SALT SHOCKIN SACCHAROMYCES-CEREVISIAE

Stress tolerance of Saccharomyces cerevisiae was examined after exposu re to heat and salt shock in the presence or absence of the protein sy nthesis inhibitor cycloheximide. Cells heat-shocked (37 degrees C for 45 min) in the absence of cycloheximide demonstrated increased toleran ce of heat, freezing and salt stress. For cells heat-shocked in the pr esence of cycloheximide, heat and salt tolerance could still be induce d, although at lower levels, while induction of freezing tolerance was completely inhibited. These results indicated that while heat shock p roteins (hsps) may contribute to induced heat and salt tolerance they are not essential, although induction of freezing tolerance appears to require protein synthesis. Exposure of cells to salt shock (300 mM Na Cl for 45 min) induced stress protein synthesis and the accumulation o f glycerol, responses analogous to induction of hsp synthesis and treh alose accumulation in cells exposed to heat shock. Cells salt-shocked in the absence of cycloheximide showed a similar pattern of induced st ress tolerance as with heat, with increased tolerance of heat, salt an d freezing. Cells salt-shocked in the presence of cycloheximide contin ued to show induced heat and salt tolerance, but freezing tolerance co uld not be induced. These results lend support to the hypothesis that hsp synthesis is not essential for induced tolerance of some forms of stress and that accumulated solutes such as trehalose or glycerol may contribute to induced stress tolerance.