Although temperature response will follow a continuum, the change from permissive to non-permissive temperatures which occurs between 38 and 42 ˚C in apple cells (within the time course of our experiments) has been found in pear fruit cells (Wu and Wallner 1983, Ferguson et al. 1994), and is in the same range as that found for heat damage and acquisition of both heat and low temperature tolerance in whole fruit (Lurie 1998).