Acclimation vs shock response to temperature and drought stress in potato cells: a comparative analysis of molecular changes

To dissect the cellular response to water stress and compare changes induced as a generalized response with those involved in tolerance/acclimation mechanisms, molecular changes were compared in cultured potato cells after graduai exposure to polyethylene glicol (PEG)-mediated low water potential versus those induced in cells abruptly exposed to the sarne stress intensity. In acclimated potato cells, active growth was maintained under conditions of low water potential which inhibited the growth of non-acclimated cells by means of a set of metabolic changes, including proline accumulation, synthesis of de novo proteins and changes in gene expression. Structure of cellular membranes was kept in acclimated cells al an osmotic potential of -2.3 MPa, which caused extended membrane disruption when applied to non-acclimated cells. Membrane phospolipids of acclimated cells were found to contain more saturated fatty acids, causing an increase in membrane microviscosity. The steady-state level of delta-9 and delta 12 desaturase gene decreased in acclimated cells, suggesting that the variation in the level of fatty acid unsaturation was at least partially associated with down- regulationof the cxpression of these genes. The level of expression of the desaturase genes was aIso regulated by changes in growth temperature. Increase in temperature caused down- regulation of delta-9 desaturase, while delta-12 desaturase was actively expressed by decreasing the temperature.