Ozone effects on high light-induced photoinhibition in Phaseolus vulgaris

In this study the response to photoinhibition of photosynthesis and subsequent recovery was examined in plants of Phaseolus vulgaris L. cultivar 'Pinto' exposed to charcoal-filtered air or to ozone (O-3) at 150 nL L-1 either for 3 h, or for 5 h. The responses were analysed using chlorophyll fluorescence imaging and by conventional fluorometry. Compared to control plants maintained in charcoal-filtered air, in plants exposed for 3 h to O-3 and then subjected to high light treatment, the results show an increased tolerance to photoinhibition. Plants exposed to the same O-3 concentration but for the longer 5-h period, were not tolerant to the photoinhibition treatment and, instead showed visible symptoms of damage (chlorosis and necrosis) clearly attributable to the longer O-3 exposure. Here the detrimental effects of O-3 aggravated the effects of the high light photoinhibitory treatment. The leaves exposed to the shorter O-3 treatment (150 nL L-1 for 3 h) developed an ability to counteract the negative effects of a high light exposure probably because the O-3 had activated an antioxidant system able to protect the photosynthetic machinery. (C) 2008 Elsevier Ireland Ltd. All rights reserved.