The role of photosynthetic activity in the response of isolated Glycine max mesophyll cells to ozone

The hypothesis that active photosynthesis results in a more severe cellular response to ozone (O3) was tested. Using suspensions of isolated soybean (Glycine max (L.) Merr. cv. Chippewa 64) mesophyll cells, we measured photosynthetic carbon fixation rates and cell viability, as determined by fluorescein diacetate staining, before and after treatment with O3 in the light and dark in the presence or absence of NaHCO3. Ozone reduced the photosynthesis rates of isolated mesophyll cells to a greater degree than cell viability, suggesting greater sensitivity of photosynthesis. Posttreatment photosynthesis rates were higher in cells that were fumigated in media containing NaHCO3 than in cells fumigated in its absence. The only interaction detected was between the gaseous treatments and light, in which relative cell viability was reduced more by O3 in the light than in the dark, in the second experiment. The interaction was, at least in part, a reflection of experimental error. Of greater significance was the observation that the photosynthetic function could be affected equally by O3 in the dark and in the light.