Adaptation of potato cells to low water potential and changes in membrane fatty acid composition and fluidity

Disruption of cellular membranes has been observed in plant tissues in response to intense water stress, with loss of membrane functionality. A stepwise adaptation allows biochemical and structural changes of cellular membranes and maintenance of membrane fluidity, which is a prerequisite of acquired tolerance (1). While an extensive literature on changes in membrane fatty acid composition induced by varying external temperatures is available (2), much less is known about the changes induced in plants under drought conditions. It has been reported that, besides variation of the major classes of lipids, the level of unsaturation of fatty acids (FA) decreases (2). The data reported deal with the changes observed in potato cells which were gradually adapted to increasing low water potentials induced by PEG 8000, which reduces free water concentration extracellularly (3). Adapted cells were able to grow actively in the presence of 20% PEG and maintained a normal ultra-structure of the main cellular and sub-cellular constituents. FA of the main extra-chloroplast phospholipids were found to be more saturated in PEG-adapted cells, compared to those in unadapted cells. These changes were associated to an increase of microviscosity of isolated protoplasts from adapted cells, as determined by steady-state fluorescence anisotropy by using diphenil-hexatriene (DPH) as a membrane probe (4).