Yeast cell response to water stress: Structural-and-functional changes and protective reactions

Anhydrobiosis is one of the most interesting phenomena of nature showing practically unlimited potentials of live organisms to survive extreme conditions of environment. Its investigations gave a lot of new information for the better understanding of water significance for the maintenance of cell viability. Using yeast cells as a simple and very convenient model the main structural and functional changes of different organelles upon strong desiccation of the eucaryotic organisms were revealed. Special attention was concentrated on the state and functional activity of nuclear, mitochondria!, vacuolar and plasma membranes. The potential possibility to improve the resistance of membranes to dehydration was shown. A variety of intracellular protective reactions directed to the maintenance of organism viability was established. The main of them are the following: chromatin and mitochondrial DNA condensation at the early stages of dehydration procedure which causes to suppression of transcriptional activity and stabilisation of DNA structure and conformation, separation by the membranes of significant portions of damaged cytoplasm and non-chromosomal regions of nucleus, synthesis and accumulation of trehalose and polyols by cells. The obtained results led us to the conclusion on the main factors affecting cell viability under extreme conditions of water stress, including intracellular nucleic acids stability level, maximum possible preservation of membrane molecular organisation, cell ability to realise a number of protective reactions at the beginning of dehydration process. It is shown the changes in cell characteristics linked with the water stress provide additional possibilities for the survival of whole yeast population on the one hand, and could be used for the directed influence of microorganisms' metabolism on the other hand.