Heat-induced protection against death of suspension-cultured apple fruit cells exposed to low temperature

Abstract

Death of suspension-cultured apple fruit cells (Malus domestica Borkh. cv. Braeburn), resulting from exposure to low temperature (1 °C), was reduced by a prior 1 h/38 °C treatment. Pre-heated chilled cells produced less ethylene, indicating lower chilling injury. Heat treatment resulted in increased transcripts for a low molecular weight (hsp17) and a 70 kDa heat shock protein (hsp), but expression weakened within 24 h following the transfer of cells to 25 °C. When cells were instead transferred to 1 °C after heat, elevated hsp gene expression persisted for up to 3 d. Flow cytometric analysis of apple cell protoplasts showed that the 1 °C treatment resulted in a subpopulation of protoplasts undergoing cell death, not observed with the 38 °C pre-treatment. Chromatin condensation did not occur with the heat treatments. These results suggest that heat-induced reduction of cell death at low temperatures may involve persistence of hsps, and low-temperature susceptibility is less likely to be associated with programmed cell death. All cells do not respond in the same way, their tolerance being associated with different states of metabolism or of the cell cycle.