title: Vacuolar membrane lesions induced by a freeze-thaw cycle in protoplasts isolated from deacclimated tubers of Jerusalem artichoke (Helianthus tuberosus L.).
abstract: The processes of freezing injury in Jerusalem artichoke (Helianthus tuberosus L.) tubers were studied using protoplasts isolated from cold-acclimated and deacclimated tubers. Prior to freezing, protoplasts were preloaded with 10 microM fluorescein diacetate (FDA) in an isotonic sorbitol solution. After freeze-thawing at various temperatures, cell viability was evaluated under a fluorescence microscope. In cold-acclimated tubers, more than 80% of protoplasts survived freezing to -20 degrees C. By contrast, in deacclimated tubers, the cell survival abruptly declined after freezing to temperatures below -5 degrees C. Thus, freezing tolerance differed significantly between protoplasts isolated from cold-acclimated and deacclimated tubers. Two distinct types of cell injury, which were caused by either damage to plasma membrane (cell-lysis type) or by damage to the vacuolar membrane (abnormal-staining type), were observed, depending on the cold hardiness and freezing temperature. In the cells of the abnormal-staining type, shrinkage of the central vacuolar space and simultaneous acidification of the cytoplasmic space were characteristically observed immediately before complete cell-rehydration during thawing. The decrease in freezing tolerance of protoplasts after deacclimation was suggested to be due mainly to destabilization of the vacuolar membrane by freeze-induced dehydration stress.
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Murai
authors.forename: S
authors.initials: S
authors.lastname: Yoshida
mesh_terms: D005615:Freezing; D007425:Intracellular Membranes; D011523:Protoplasts; D014617:Vacuoles; D014675:Vegetables