Ozone exposure affects photosynthesis of pumpkin (<i>Cucurbita pepo</i>) plants

Abstract

Summary Physiological and biochemical responses of the ozone (O 3 )‐sensitive pumpkin cultivar ( Cucurbita pepo ‘Ambassador’) to O 3 exposure are reported here to determine critical O 3 concentrations related to duration of pollutant exposure. Pumpkin plants were exposed to 150 nl l −1 of O 3 for 5 h d −1 for 5 d. Gas‐exchange, chlorophyll a fluorescence and pigment‐content measurements were determined on days 1, 3, 5 for young leaves and days 1, 3, 4 for the mature leaves of control and treated plants. In both young and mature leaves, O 3 induced a significant decrease in photosynthetic rate through impacts on stomata and photochemistry. A reduction in PSII photochemistry, photochemical quenching and quantum yield, accompanied by a parallel increase in nonphotochemical quenching was detected. Following O 3 treatment the pool of xanthophyll cycle pigments and the de‐epoxidation index underwent a significant increase, whereas chlorophylls and β‐carotene were less affected. The results showed that most of the parameters were affected by O 3 after 1 d of exposure and indicated an overall effect of O 3 and days of treatment, irrespective of leaf age.