Membrane behavior as influenced by partitioning of amphiphiles during drying : a comparative study in anhydrobiotic plant systems

During cellular desiccation, reduction in volume can in principle cause amphiphilic compounds to partition from the cytoplasm into membranes, with structural perturbance as the result. Here, we studied the effect of partitioning of endogenous amphiphiles on membrane surface dynamics in desiccation-tolerant and -intolerant, higher and lower plant systems, using electron paramagnetic resonance (EPR) spin probe techniques. Labeling cells with the amphiphilic spin probe perdeuterated TEMPONE (PDT) enabled partitioning into the various phases to be followed. During drying, PDT molecules preferentially partitioned from the aqueous cytoplasm into the membrane surface and, at advanced stages of water loss, also into oil bodies. There was no specific partition behavior that could be correlated with lower/higher plants or with desiccation-tolerance. In vivo labeling with 5-doxylstearate (5-DS) enabled membrane surface fluidity to be characterized. In hydrated plants, the 5-DS spectra contained an immobile and a fluid component. The characteristics of the immobile component could not be specifically correlated with either lower or higher plants, or with desiccation tolerance. The relative contribution of the fluid component to the 5-DS spectra was higher in lower plants than in higher plants, but considerably decreased with drying in all desiccation-tolerant organisms. In contrast, the proportion of the fluid component in desiccation-sensitive wheat seedling root was higher than that in desiccation-tolerant wheat axis and considerably increased at the onset of water loss. We suggest that partitioning of amphipaths fluidize the membrane surface, but that in desiccation-tolerant systems the membranes are protected from excessive fluidization