Influences of subcellular Ca redistribution induced by γ irradiation on the fruit firmness of refrigerated blueberries

To investigate influences of intracellular calcium (Ca) redistribution induced by irradiation treatments on the firmness of refrigerated blueberries, 'Bluecrop' blueberry fruit were irradiated with gamma (γ) ray at doses of 0.5, 1.0, and 2.5 kGy and unirradiated fruit served as the control (CK). The influences of different irradiation doses on changes in intracellular Ca2+ fluorescence signals and subcellular Ca distribution were evaluated, as well as correlations of these changes with the firmness of refrigerated blueberry fruit. Results showed that irradiation treatment could induce blueberry pulp cells to produce Ca2+ fluorescence signals and increase the intracellular Ca2+ concentration. In addition, the greater the dose during irradiation, the more significant its effect. In the refrigeration period, the intracellular Ca distribution had no effect on fruit firmness of blueberries irradiated at 0.5 kGy. Whereas, irradiated at 1.0 and 2.5 kGy could make Ca content increase in cell walls and decrease in organelle and cytoplasm, thus promoting Ca accumulation in cell wall at early stage of storage. Subcellular Ca redistribution induced by irradiation at 1.0 kGy was not related to the fruit firmness of refrigerated blueberries, but irradiation at 2.5 kGy could promote the migration of intracellular Ca to cell wall, which exerted a positive effect on the fruit firmness of refrigerated blueberries.