Description:
<jats:title>ABSTRACT</jats:title><jats:p>The responses of C<jats:sub>3</jats:sub> plants to rising atmospheric CO<jats:sub>2</jats:sub> levels are considered to be largely dependent on effects exerted through altered photosynthesis. In contrast, the nature of the responses of C<jats:sub>4</jats:sub> plants to high CO<jats:sub>2</jats:sub> remains controversial because of the absence of CO<jats:sub>2</jats:sub>‐dependent effects on photosynthesis. In this study, the effects of atmospheric CO<jats:sub>2</jats:sub> availability on the transcriptome, proteome and metabolome profiles of two ranks of source leaves in maize (<jats:italic>Zea mays</jats:italic> L.) were studied in plants grown under ambient CO<jats:sub>2</jats:sub> conditions (350 +/− 20 <jats:italic>µ</jats:italic>L L<jats:sup>−1</jats:sup> CO<jats:sub>2</jats:sub>) or with CO<jats:sub>2</jats:sub> enrichment (700 +/− 20 <jats:italic>µ</jats:italic>L L<jats:sup>−1</jats:sup> CO<jats:sub>2</jats:sub>). Growth at high CO<jats:sub>2</jats:sub> had no effect on photosynthesis, photorespiration, leaf C/N ratios or anthocyanin contents. However, leaf transpiration rates, carbohydrate metabolism and protein carbonyl accumulation were altered at high CO<jats:sub>2</jats:sub> in a leaf‐rank specific manner. Although no significant CO<jats:sub>2</jats:sub>‐dependent changes in the leaf transcriptome were observed, qPCR analysis revealed that the abundance of transcripts encoding a Bowman–Birk protease inhibitor and a serpin were changed by the growth CO<jats:sub>2</jats:sub> level in a leaf rank specific manner. Moreover, CO<jats:sub>2</jats:sub>‐dependent changes in the leaf proteome were most evident in the oldest source leaves. Small changes in water status may be responsible for the observed responses to high CO<jats:sub>2,</jats:sub> particularly in the older leaf ranks.</jats:p>