Modulation of photosystem 2 reactions mediated by aluminium toxicity in Zea mays

Two weeks old maize (Zea mays L. cv. XL-72.3) plants were submitted to 0 to 81 g m-3 Al for 20 d in a growth medium of low ionic strength. The increasing Al concentrations sharply increased chlorophyll (Chl) concentrations. The rates of photosystem 2 activities (H2O→DCPIP and DPC→DCPIP) increased at 9 g(Al) m-3 but at higher Al doses they decreased again. A slight decrease of qE and qN coupled to an increase of qP was also observed until the 27 g m-3 Al. The Al-induced decline in cytochrome (cyt) b contents per Chl unit was parallel for the b559LP and cyt b559HP forms, but on a leaf area basis more or less opposite trend in both these cyt forms was observed. Increased Al concentrations also decreased carotene and zeaxanthin contents.