Light- and low temperature-induced accumulation of anthocyanins attenuates the oxidation risk without limiting photosynthesis in maize leaves

Abstract

The protection of photosynthesis from the photo-oxidative risk in the maize (Zea mays L.) line HOPI, which shows a large accumulation of anthocyanins (Ant) in the illuminated leaf side, has been investigated by comparing effects of white and red light sources, this latter not being absorbed by these pigments. Plants of HOPI and of its green mutant W22, unable to synthesise anthocyanins, were grown for 25 days at 800 µmol m-2s-1 and at 25/20°C and then for two days at 18°C to enhance the leaf flushing. Both chlorophyll (Chl) a and b content was the same in the two lines while total carotenoids were slightly higher in HOPI than in W22. The anthocyanin content of red leaves was 8 µg cm-2. A photoinhibition treatment at 7°C indicated that anthocyanins accumulated in the vacuoles of the illuminated epithelial cells shade chloroplasts. A 50% reduction of the ratio between variable and maximum chlorophyll fluorescence (Fv/Fm) occurred in HOPI at a combination of low temperature with a white light that was half that in W22. This reduced the photo-oxidative risk for chloroplasts so that a lower total superoxide dismutase (SOD) activity was found in HOPI leaves with respect to W22 leaves. At the same time, anthocyanins did not shade, for their particular localisation, the chloroplasts in the guard cells and water transpiration was almost the same in the two lines. Similarly, CO2 uptake of HOPI leaves was close to that of W22. Other implications on photosynthesis of leaf anthocyanins accumulation will be discussed.