The effects of elevated CO2 concentrations on cell division rates, growth patterns, and blade anatomy in young wheat plants are modulated by factors related to leaf position, vernalization, and genotype

This study demonstrates that elevated [CO2] has profound effects on cell division and expansion in developing wheat (Triticum aestivum L.) leaves and on the quantitative integration of these processes in whole-leaf growth kinetics, anatomy, and carbon content. The expression of these effects, however, is modified by intrinsic factors related to genetic makeup and leaf position, and also by exposure to low vernalizing temperatures at germination. Beyond these interactions, leaf developmental responses to elevated [CO2] in wheat share several remarkable features that were conserved across all leaves examined. Most significantly: (a) the contribution of [CO2] effects on meristem size and activity in driving differences in whole-blade growth kinetics and final dimensions; (b) an anisotropy in cellular growth responses to elevated [CO2], with final cell length and expansion in the paradermal plane being highly conserved, even when the rates and duration of cell elongation were modified, while cell cross-sectional areas were increased; (c) tissue-specific effects of elevated [CO2], with significant modifications of mesophyll anatomy, including an increased extension of intercellular air spaces and the formation of, on average, one extra cell layer, while epidermal anatomy was mostly unaltered. Our results indicate complex developmental regulations of sugar effects in expanding leaves that are subjected to genetic variation and influenced by environmental cues important in the promotion of floral initiation. They also provide insights into apparently contradictory and inconsistent conclusions of published CO2 enrichment studies in wheat.