Effects of SO2 and O3 on Allocation of 14C-Labeled Photosynthate in Phaseolus vulgaris

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Abstract
A series of laboratory exposures of two varieties of bush bean (Phaseolus vulgaris L., var 274 and var 290) was conducted to determine the sensitivity of [14C]photosynthate allocation patterns to alteration by SO2 and O3. Experiments with the pollution-resistant 274 variety demonstrated short-term changes in both 14C and biomass allocation to roots of 14CO2-labeled plants but no significant effect on yield by up to 40 hours of exposure to SO2 at 0.50 microliters per liter or 4 hours of O3 at 0.40 microliters per liter. Subsequent experiments with the more sensitive 290 variety demonstrated significant alteration of photosynthesis, translocation, and partitioning of photosynthate between plant parts including developing pods. Significant increases in foliar retention of photosynthate (+40%) occurred after 8 hours of exposure to SO2 at 0.75 microliters per liter (6.0 microliters per liter-hour) and 11 hours of exposure to O3 at 0.30 microliters per liter-hour (3.3 microliters-hours). Time series sampling of labeled tissues after 14CO2 uptake showed that the disruption of translocation patterns was persistent for at least 1 week after exposures ceased. Subsequent longer-term exposures at lower concentrations of both O3 (0.0, 0.10, 0.15, and 0.20 microliters per liter) and SO2 (0.0, 0.20, and 0.40 microliters per liter) demonstrated that O3 more effectively altered allocation than SO2, that primary leaves were generally more sensitive than trifoliates, and that responses of trifoliate leaves varied with plant growth stage. Altered rates of allocation of photosynthate by leaves were generally associated with alterations of similar magnitude and opposite direction in developing pods. Collectively, these experiments suggest that allocation patterns can provide sensitive indices of incipient growth responses of pollution-stressed vegetation.