Dehydration-induced redistribution of amphiphilic molecules between cytoplasm and lipids is associated with desiccation tolerance in seeds

This study establishes a relationship between desiccation tolerance and the transfer of amphiphilic molecules from the cytoplasm into lipids during dr ying, using electron paramagnetic resonance spectroscopy of amphiphilic spi n probes introduced into imbibed radicles of pea (Pisum sativum) and cucumb er (Cucumis sativa) seeds. Survival following drying and a membrane integri ty assay indicated that desiccation tolerance was present during early imbi bition and lost in germinated radicles. In germinated cucumber radicles, de siccation tolerance could be re-induced by an incubation in polyethylene gl ycol (PEG) before drying. In desiccation-intolerant radicles, partitioning of spin probes into lipids during dehydration occurred at higher water cont ents compared with tolerant and PEG-induced tolerant radicles. The differen ce in partitioning behavior between desiccation-tolerant and -intolerant ti ssues could not be explained by the loss of water. Consequently, using a tw o-phase model system composed of sunflower or cucumber oil and water, physi cal properties of the aqueous solvent that may affect the partitioning of a mphiphilic spin probes were investigated. A significant relationship was fo und between the partitioning of spin probes and the viscosity of the aqueou s solvent. Moreover, in desiccation-sensitive radicles, the rise in cellula r microviscosity during drying commenced at higher water contents compared with tolerant or PEG-induced tolerant radicles, suggesting that the microvi scosity of the cytoplasm may control the partitioning behavior in dehydrati ng seeds.