CHLOROPHYLL FLUORESCENCE AS ON INDICATOR TO DETECT DEFFERENTIAL TOLERANCE OF SNAPBEAN CULTIVARS IN RESPONSE TO O3 STRESS

The potential use of chlorophyll fluorescence (CF) induction assay as a tool for screening and characterizing the tolerance of ozone (O3), contrasting cultivars of snapbeans (Phaseolus vulgaris L.), was investigated. A range of CF parameters was examined for snapbeans treated with O3. Chlorophyll fluorescence parameters such as Fo, Fmax, and Fv, Fv/Fmax were compared in O3 tolerant and susceptible snapbeans cultivars grown under O3 stress conditions. O3-stressed leaves showed significantly higher constant-yield (Fo) but greatly reduced variable fluorescence (Fv) and decreased Fv/Fmax ratios. In the O3-sensitive cultivar snapbean cv BBL-290, O3 stress resulted in a strong inhibition of the fast and slow fluorescence-induction transients and altered the form of the kinetic curves of CF in leaves. In particular, the fluorescence quenching rate and Fv/Fmax ratios were markedly decreased in O3-stressed leaves. In contrast, leaves of the O3-resistant cultivar cv Astro showed only minor changes in CF. The values of the Fv/Fmax ratio decreased in the O3-sensitive cultivar much more drastically than the O3-resistant cultivar. Based on CF measurements, it appears that O3-induced stress blocked photosynthetic electron transport between photosystem (PS) II and PS I. The close agreement between changes in fluorescence and visual symptoms of O3-induced injury suggest that the CF patterns, the rate of fluorescence-induction transients, and the Fv/Fmax ratio can provide valuable tools to investigate the photosynthetic and metabolic mechanisms affects by O3-induced stress. Chlorophyll fluorescence analysis could also be a useful technique which could be used by plant breeders to screen large numbers of plant reapidly for air pollution sensitivity.