Phase transitions in microsomal membranes from chilling sensitive and chilling resistant tomato plants and fruit

Abstract

The thermal response of tonoplast enriched microsomal membranes from the leaves and mature green fruit pericarp of two tomato varieties was determined by electron paramagnetic resonance (EPR), differential scanning calorimetry (DSC) and fluorescence polarization spectroscopy. Chilling sensitive Lycopersicon esculentum cv. Heinz-722 and a chilling resistant hybrid of cv. H-722 and L. hirsutum (F-4 generation, strain 58-1), were used for comparative studies. Lipid phase transitions in the microsomal membranes were detected. Transition temperatures were determined by EPR at 12† for the chilling sensitive leaf and fruit and at 4 and 8† for the chilling resistant leaf and fruit, respectively, using 12-doxystearic acid as a spin label. Phase transitions were not detected in 1,6-diphenylhexatriene labelled membranes by fluorescence depolarization. Broad transitions (50† range) were observed by DSC in the sensitive fruit and leaves while none were evident in the resistant counterparts. In vivo chlorophyll fluroscence of the leaves showed a greater quenching of fluorescence in the sensitive leaves while ultrastructural studies of the fruit indicated a loss of cytoplasmic structure in the sensitive fruit, but not in the resistant fruit. These results indicate that membrane phase transition temperatures can be used as an indicator of resistance towards chilling.