Biology subjects

Roddy, A. B.

Publications and source records attributed to Roddy, A. B..

3 recordsLinked to original sources

bioRxiv2020

Maximum CO2 diffusion inside leaves is limited by the scaling of cell size and genome size

Maintaining high rates of photosynthesis in leaves requires efficient movement of CO2 from the atmosphere to the chloroplasts inside the leaf where it is converted into sugar. Throughout the evolution of vascular plants, CO2 diffusion across the leaf surface was maximized by reducing the sizes of the guard cells that form stomatal pores in the leaf epidermis1,2. Once inside the leaf, CO2 must diffuse through the intercellular airspace and into the mesophyll cells where photosynthesis occurs3,4. However, the diffusive interface defined by the mesophyll cells and the airspace and its coordinated evolution with other leaf traits are not well described5. Here we show that among vascular plants variation in the total amount of mesophyll surface area per unit mesophyll volume is driven primarily by cell size, the lower limit of which is defined by genome size. The higher surface area enabled by smaller cells allows for more efficient CO2 diffusion into photosynthetic mesophyll cells. Our results demonstrate that genome downsizing among the flowering plants6 was critical to restructuring the entire pathway of CO2 diffusion, facilitating high rates of CO2 supply to the leaf mesophyll cells despite declining atmospheric CO2 levels during the Cretaceous.

plant biology↗

bioRxiv2017

Water relations of Calycanthus flowers: hydraulic conductance, capacitance, and embolism resistance

Introduction Introduction Materials Methods Results Discussion Conclusions References Flowers are developmentally and morphologically complex structures whose primary function is to promote sexual reproduction (Specht & Bartlett 2009). Coevolution with animal pollinators has long been considered the primary selective agent responsible for the many, diverse forms apparent among angiosperm flowers (Sprengel 1793, 1996; Fenster et al. 2004). Yet, floral adaptations to pollinators may not be as frequent as commonly considered, and non-pollinator agents of selection, such as the resource costs of building and maintaining flowers, may also influence floral form and function (Herrera 1996; Strauss & Whittall 2006). Fo ...

ecology↗

bioRxiv2017

Genome downsizing, physiological novelty, and the global dominance of flowering plants

During the Cretaceous (145-66 Ma), early angiosperms rapidly diversified, eventually outcompeting the ferns and gymnosperms previously dominating most ecosystems. Heightened competitive abilities of angiosperms are often attributed to higher rates of transpiration facilitating faster growth. This hypothesis does not explain how angiosperms were able to develop leaves with smaller, but densely packed stomata and highly branched venation networks needed to support increased gas exchange rates. Although genome duplication and reorganization have likely facilitated angiosperm diversification, here we show that genome downsizing facilitated reductions in cell size necessary to construct leaves with a high density stomata and veins. Rapid genome downsizing during the early Cretaceous allowed angiosperms to push the frontiers of anatomical trait space. In contrast, during the same time period ferns and gymnosperms exhibited no such changes in genome size, stomatal size, or vein density. Further reinforcing the effect of genome downsizing on increased gas exchange rates, we found that species employing water-loss limiting crassulacean acid metabolism (CAM) photosynthesis, have significantly larger genomes than C3 and C4 species. By directly affecting cell size and gas exchange capacity, genome downsizing brought actual primary productivity closer to its maximum potential. These results suggest species with small genomes, exhibiting a larger range of final cell size, can more finely tune their leaf physiology to environmental conditions and inhabit a broader range of habitats.

ecology↗