Decline of activity and quantity of ribulose bisphosphate carboxylase/oxygenase and net photosynthesis in ozone-treated potato foliage

The effect of ozone (O₃) on ribulose bisphosphate carboxylase/oxygenase (Rubisco) activity and quantity and net photosynthesis in greenhouse-grown Solanum tuberosum L. cv `Norland' foliage was studied in relation to oxidant-induced premature senescence. Plants, 26 days old, were exposed to 0.06 to 0.08 microliters per liter O₃ from 1000 to 1600 hours for 4 days in a controlled environment chamber. On day 5, plants were exposed to a 6-hour simulated inversion in which O₃ peaked at 0.12 microliters per liter. Net photosynthesis declined in response to O₃ but recovered to near control levels 3 days after the exposure ended. Rubisco activity and quantity in control potato foliage increased and then decreased during the 12-day interval of the study. In some experiments foliage studied was physiologically mature and Rubisco activity had peaked when O₃ exposure commenced. In those cases, O₃ accelerated the decline in Rubisco activity. When less mature foliage was treated with O₃, the leaves never achieved the maximal level of Rubisco activity observed in control foliage and also exhibited more rapid decline in initial and total activity. Percent activation of Rubisco (initial/total activity) was not affected significantly by treatment. Quantity of Rubisco decreased in concert with activity. The decrease in activities is most likely due to a decrease in available protein rather than a decrease in the percentage of Rubisco activated in vivo. The reduction in the quantity of Rubisco, an important foliar storage protein, could contribute to premature senescence associated with toxicity of this air pollutant.