DRYING INCREASES INTRACELLULAR PARTITIONING OF AMPHIPHILIC SUBSTANCESINTO THE LIPID PHASE - IMPACT ON MEMBRANE-PERMEABILITY AND SIGNIFICANCE FOR DESICCATION TOLERANCE

Previously we proposed that endogenous amphiphilic substances may part ition from the aqueous cytoplasm into the lipid phase during dehydrati on of desiccation-tolerant organ(ism)s and vice versa during rehydrati on. Their perturbing presence in membranes could thus explain the tran sient leakage from imbibing organisms. To study the mechanism of this phenomenon, amphiphilic nitroxide spin probes were introduced into the pollen of a model organism, Typha latifolia, and their partitioning b ehavior during dehydration and rehydration was analyzed by electron pa ramagnetic resonance spectroscopy. In hydrated pollen the spin probes mainly occurred in the aqueous phase; during dehydration, however, the amphiphilic spin probes partitioned into the lipid phase and had disa ppeared from the aqueous phase below 0.4 g water g(-1) dry weight. Dur ing rehydration the probes reappeared in the aqueous phase above 0.4 g water g(-1) dry weight. The partitioning back into the cytoplasm coin cided with the decrease of the initially high plasma membrane permeabi lity. A charged polar spin probe was trapped in the cytoplasm during d rying. Liposome experiments showed that partitioning of an amphiphilic spin probe into the bilayer during dehydration caused transient leaka ge during rehydration. This was also observed with endogenous amphipat hs that were extracted from pollen, implying similar partitioning beha vior. In view of the fluidizing effect on membranes and the antioxidan t properties of many endogenous amphipaths, we suggest that partitioni ng with drying may be pivotal to desiccation tolerance, despite the ri sk of imbibitional leakage.