Anthocyanin accumulation in the illuminated surface of maize leaves enhances protection from photo-inhibitory risks at low temperature, without further limitation to photosynthesis

At suboptimal temperatures, anthocyanins accumulate in the illuminated leaf surface of some maize genotypes and, if the anthocyanins shade chloroplasts, they can effectively reduce the risk of photo-inhibition but also photo-synthesis. To investigate this phenomenon, gas exchange, fluorescence, superoxide dismutase activity and xantho-phyll composition of anthocyanin-containing HOPI and anthocyanin-deficient W22 maize genotypes were measured in either white or red light, where the latter is not absorbed by anthocyanins. Despite differences in light absorption in chloroplasts, photosynthesis did not differ between HOPI and W22 under either light source, suggesting that neither CO2 supply nor photochemistry were more limiting in red leaves than in green leaves. In fact, no major differences in transpiration were detected. The DeltaF/F-m (photosystem II quantum yield) of HOPI in white light was higher than in red light and higher than DeltaF/F-m of W22 with either light source. This probably compensated for the lower white light absorption of HOPI chloroplasts compared with W22 because of the presence of anthocyanins and led to similar rates of calculated electron transport for both genotypes. After exposure to high white light at 5 degreesC, xanthophyll de-epoxidation and superoxide dismutase activity were lower in HOPI than in W22. Further, HOPI could be exposed to a much higher irradiance than W22 before F-v/F-m was reduced to that of W22.