Heat stress responses in cultured plant cells : development and comparison of viability tests

The response of suspension-cultured pear (Pyrus communis cv Bartlett) cells to heat stress was studied using three viability tests: regrowth (culture growth during 10 days after stress); triphenyltetrazolium chloride reduction; and electrolyte leakage. Critical (50% injury) temperatures for a 20-minute exposure were 42 degrees , 52 degrees , and 56 degrees C, respectively, for these viability tests. Electrolyte leakage had the lowest temperature coefficient. Heat stress inhibition of triphenyltetrazolium chloride reducing capacity was much greater if the viability test was conducted 3 days, rather than immediately, after the stress treatment. Consistent with a major role for indirect metabolic strain in heat injury, treatment with 3.6 micromolar cycloheximide and heat stress (20 minutes at 43 degrees C) affected culture regrowth similarly. We conclude that the measurements of direct response are not adequate substitutes for regrowth tests in assessing heat injury to cultured plant cells.