AUTHOR=Huang Wenmin , Han Shijuan , Xing Zhenfei , Li Wei TITLE=Responses of Leaf Anatomy and CO2 Concentrating Mechanisms of the Aquatic Plant Ottelia cordata to Variable CO2 JOURNAL=Frontiers in Plant Science VOLUME=11 YEAR=2020 URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.01261 DOI=10.3389/fpls.2020.01261 ISSN=1664-462X ABSTRACT=

Acclimation to variable CO₂ was studied in floating leaves of the freshwater monocot Ottelia cordata grown in either low or high CO₂. The most striking anatomical variations responding to high CO₂ included the enlarged upper epidermal cells and the decreased area of epidermal chloroplasts. Stomata that distributed on the upper surface, and the stomatic chamber area, showed no significant response to high CO₂. pH-drift experiments indicated that floating leaves of O. cordata were able to use bicarbonate regardless of CO₂ concentrations. Photosynthetic enzyme activities and patterns of organic acids fluctuation confirmed that floating leaves of O. cordata can operate CAM only at low CO₂, and perform C₄-like metabolism at both high and low CO₂. Overall, the present results imply that the floating leaves of O. cordata does not just rely on the atmospheric CO₂ for its inorganic carbon, but is also dependent on CO₂ and bicarbonate in the water. By showing these effects of CO₂ variation, we highlight the need for further experimental studies on the regulatory mechanisms in O. cordata floating leaves, that prevent futile cycling among the three CO₂ concentrating mechanisms (bicarbonate use, C₄, and CAM metabolism) and the strategy for exploiting atmospheric CO₂, as well as studies on the detailed biochemical pathway for C₄ and CAM metabolism in this species.