METHOD: Light Stress CONDITIONS: Lab - 14h light at 15/20C with 55-70% RH METHOD NARR: Three different experiments were conducted. #1: Simulation of natural freeze thaw stress. #2: Comparison of protocols (Slow, Fast and Flash Fg). #3: Comparison of two freezing rates on a single leaflet (Slow and Fast Freeze). Photosynthesis, respiration and ion leakage (membrane permeability) were measured. RESULTS NARR: Respiration (R) photosynthesis (PS) aniffered markedly in their sensitivity to freeze-thaw stress. Various freeze-thaw protocols had dramatically different effects on R, PS and MP while min. tissue temps remained steady. PS was much more sensitive to freeze-thaw s showed the largest decline while supercooling had no inhibition. Chloroplast, mitochondrial and cell membrane function differ in their sensitivity to realistic freeze-thaw stress. The conclusions are highly dependent on the freeze-tSlight increases in freezing rates above those normally occuring in nature can mean the difference between cell survival and death. AUTHOR EXPLANATION: Climatological data demonstrates that air cooling rates in the subz 2C/hour even during extreme drops in temp. in Wisconsin. Stress associated with ice formation, not simply tissue temp. is an important factor in freezing injury.