Ozone sensitivity of four Pakchoi cultivars with different leaf colors: physiological and biochemical mechanisms

Ozone (O-3) is important air pollutant inducing severe losses of horticultural production. Cultivars of the same species, but with different leaf colors, may differ in their ozone sensitivity. However, it has not been clarified yet if different leaf coloration influences such a sensitivity. In this study, two purple-leafed and two green-leafed cultivars of Pakchoi were selected for ozone fumigation (240 +/- 20 nmol mol(-1), 09:00-16:00 h). Elevated O-3 decreased chlorophyll content, increased anthocyanin (Ant) content, damaged cell membrane integrity, enhanced antioxidative enzyme activities, depressed photosynthetic rate (P (N)) and stomatal conductance (g (s)), inhibited maximal quantum yield (F-v/F-m) and effective quantum yield [Y-II] of PSII photochemistry, and caused visible injury. Purple-leafed cultivars with higher Ant contents were more tolerant than green-leafed cultivars as indicated by lower relative enhancement in malondialdehyde content and lower relative losses in P (N), g (s), F-v/F-m, and Y-II. The higher ability to synthesize Ant in the purple-leafed cultivars contributed to their higher photoprotective ability.