ABSTRACT
As a unicellular organism yeast is exposed to many types of environmental insult, including sudden changes in temperature, desiccation, oxidative and osmotic stress, exposure to high salt or heavy metal ions or toxic chemicals. In order to combat these insults yeast cells have evolved a wide range of responses to many different types of stress, including osmotic, heat, oxidative, starvation, low pH and organic solvents (including the toxic effects of ethanol). Some of these defences are intrinsic (constitutive) and depend on the prior physiological or metabolic conditions under which the yeast has been grown, especially important are the growth phase and the stage of the organism in its life cycle. Other defence systems are inducible following stress. The inducible responses differ from one stress to another, but it is now clear that these can be overlapping, so that acquisition of resistance to one form of stress leads to cross resistance to others. The existence of regulatory pathways leading to induction of resistance comes from a range of sensing systems, identified by signal transduction pathways and the transcription factors they influence; these form an important part of the stress responses in yeast and are presently very actively under study. More recently, it has been recognised that complex processes such as cell division are sensitive to stressinduced damage to the cells. Often the stress response can lead to cell cycle arrest while the cell sorts out the damage induced.
