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Studies of temperature stress in cultured pear cells




Wu, Min-Tze, author
Wallner, Stephen J., advisor
Ross, Cleon, committee member
Stack, Stephen, committee member
Bedford, Joel S., committee member
Hughes, Harrison G., committee member

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Studies were undertaken to examine the heat stress and freezing stress responses of cultured plant cells. Suspension- cultured pear (Pyrus communis cv. Bartlett} cells were used as the experimental materials. The response of pear 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 temperatures (those causing 50% injury} for a 20 minute exposure were 42°, 52°, and 56°C , respectively, for these viability tests. The measurements of direct response, i. e., TTC reduction and electrolyte leakage, were not adequate substitutes for regrowth tests in assessing heat injury to cultured plant cells. The pipetting of pear suspension cultures was followed by a substantial but transient decrease in heat sensitivity. During a culture cycle, pear cells were most sensitive to heat at around day three. The influence of these normal culture variables (handling and age) are potentially serious artefacts and must be well characterized in order to minimize systematic errors in measuring heat tolerance. Beyond this, they may provide clues concerning physiological factors governing the responses of cells to heat. Both elevated growth temperature and brief heat shock increased the heat tolerance of pear cells. Several features of heat acclimation induced by these two methods were compared. Based on these comparisons, it was concluded that heat acclimation in response to growth at 30°C and to heat shock occurred via different mechanisms. The effect of low temperature on heat tolerance and high temperature on freezing tolerance of pear cells was also examined. The heat acclimation induced by elevated growth temperature increased freezing tolerance, but cold acclimation did not increase heat tolerance. It seems likely that some component(s) of cold and heat acclimation may be the same. This indicates that studies of response to different stimuli may help in clarifying mechanisms of temperature acclimation. The only potential mechanism examined in this study was the role of extracellular polysaccharides in cell response to freezing stress. Extracellular macromolecules from non-acclimated cultures aggregated irreversibly during freezing, while those from acclimated cultures did not. The aggregation of polysaccharides may be related to the observation that macromolecules from a non-acclimated medium increased the freezing injury of pear cells. Analyses of polysaccharides from acclimated and non-acclimated cultures indicated that the polysaccharides were changed during cold acclimation.


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Plants -- Effect of temperature on


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