Heat-induced oxidative activity protects suspension-cultured plant cells from low temperature damage.

A short heat pre-treatment (1 h at 38°C) was found to protect both suspension-cultured apple fruit cells and tobacco cells from cold-induced cell death. Tobacco cells were more sensitive to low temperatures than apple cells, with significant cell death after 48 h at 0 or -2°C. Real-time measurements of HO levels during the heat pre-treatment revealed a substantial burst of this reactive oxygen species in both cell types. Real-time and longer-term measurements also showed a large burst of HO production from tobacco cells, but not apple cells, when exposed to low temperatures. Lower temperatures reduced levels of peroxidase activity (both total and intracellular), with the heat pre-treatment preventing some of the cold-induced reduction of this activity in both apple and tobacco cells. The greater sensitivity to low temperature of the tobacco cells may be related to higher HO production, with the heat treatment maintaining higher peroxidase activity. The lesser sensitivity of the apple cells may be due to the lack of a HO burst and maintenance of peroxidase activity by the heat treatment. These results support a role for oxidative metabolism in the beneficial effects of heat in inducing low temperature tolerance.