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Jane M. Petitte and Douglas P. Ormrod

The effects of SO2 and NO2, singly and in combination, on the growth and physiology of nontuberizing Solarium tuberosum L. `Russet Burbank' plants were studied in controlled conditions. Plants were exposed to 0.11 μl SO2 and/or 0.11 μl NO2/liter for 24 hours a day up to 10 days. Statistically significant effects were observed mainly in the SO2+ NO2 treatments compared with the control plants. Leaf area was reduced from day 2 onward, and root fresh and dry weights were reduced from day 4 onward. Significant reductions in leaf and stem dry weights occurred on day 6. Net CO2 exchange rates were reduced for SO2 exposed compared with control plants beginning on day 3, while water loss rates were increased with SO2 + NO2 beginning on day 3. The increases in water loss rate were possibly due to the development of cuticular injury observed as abaxial glazing on the upper and middle canopy leaves. Leaf osmotic potential (π) of plants with SO2 + NO2 became more negative within the first 24 hours of the exposure. This reduction was accompanied by an increase in reducing sugar concentration. Xylem water potential was reduced in the mature and expanding leaflets by day 2 of the SO2 + NO2 exposure. The most sensitive aspect of the action of SO2 + NO2 appeared to be the increase in reducing sugars that affected osmotic potential in the leaves. Considering the retardation of root growth, these data suggest that the pollutant gases may have interfered with partitioning of dry matter from the leaves to the roots.