Impact of ozone on the photosynthetic and metabolic properties of Zea mays

English: The impact of elevated ozone concentrations on plants has important global implications for the environment and especially for crop production. The fact that ozone can cause serious damage to crop production served as motivation for the research done during this study. One of South Africa’s most common agricultural crops, Zea mays, was chosen as test organism. The aim was to get a better understanding of the effect of ozone on maize. During this study we investigated the photosynthetic and metabolic responses of Zea mays after it had been exposed to moderate concentrations of ozone. The plants were grown in a green house until they reached the two-leave stage. Thereafter they were placed in a controlled environment growth chamber, where they were fumigated with ozone at 150ppb. After fumigation, leaves of the exposed plants were dark adapted for 15 minutes, before chlorophyll fluorescence measurement were made. Ozone fumigation resulted in an increase in the FO, compared to the control. Noticeable was also the lower FM values of fumigated plants. The photochemical quenching of the fumigated plants was significantly lower than the controls, while the opposite was seen for non-photochemical quenching. Several fluorescence indicators and quenching parameters were used to determine the photosynthesis potential following ozone exposure. We could also evaluate the quantum yield of PS II, which gives an estimate of the rate of linear electron transport. The effect of ozone fumigation on PR proteins (β-1, 3-glucanase and chitinase), phenolic acid composition and the hydrogen peroxide (H2O2) concentrations were also measured. H2O2 production was induced following the ozone exposure. The increase in H2O2 corresponded with the increases in β-1, 3-glucanase and chitinase activity and we concluded that if corresponded to an activation of the defence genes. Down-stream defence responses continued after exposure, with the synthesis of phenolic compounds, as indicated by increased phenolic acid concentrations. This was seen as a manifestation of the hyper sensitive response of Zea mays, which forms part of this crop’s defence response against ozone. We also conclude that ozone is a major stressor that could influence crop yields significantly.