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

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