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Summary: Certain species in the Brassicaceae family exhibit high photosynthesis rates, potentially providing a valuable route toward improving agricultural productivity. However, factors contributing to their high photosynthesis rates are still unknown.We compared Hirschfeldia incana, Brassica nigra, Brassica rapa and Arabidopsis thaliana, grown under two contrasting light intensities.Hirschfeldia incana matched B. nigra and B. rapa in achieving very high photosynthesis rates under high growth‐light condition, outperforming A. thaliana. Photosynthesis was relatively more limited by maximum photosynthesis capacity in H. incana and B. rapa and by mesophyll conductance in A. thaliana and B. nigra. Leaf traits such as greater exposed mesophyll specific surface enabled by thicker leaf or high‐density small palisade cells contributed to the variation in mesophyll conductance among the species. The species exhibited contrasting leaf construction strategies and acclimation responses to low light intensity. High‐light plants distributed Chl deeper in leaf tissue, ensuring even distribution of photosynthesis capacity, unlike low‐light plants.Leaf anatomy of H. incana, B. nigra and B. rapa facilitated effective CO2 diffusion, efficient light use and provided ample volume for their high maximum photosynthetic capacity, indicating that a combination of adaptations is required to increase CO2‐assimilation rates in plants. [ABSTRACT FROM AUTHOR]

Chloroplasts movement within mesophyll cells in C4 plants is hypothesized to enhance the CO2 concentrating mechanism, but this is difficult to verify experimentally. A three-dimensional (3D) leaf model can help analyse how chloroplast movement influences the operation of the CO2 concentrating mechanism. The first volumetric reaction–diffusion model of C4 photosynthesis that incorporates detailed 3D leaf anatomy, light propagation, ATP and NADPH production, and CO2, O2 and bicarbonate concentration driven by diffusional and assimilation/emission processes was developed. It was implemented for maize leaves to simulate various chloroplast movement scenarios within mesophyll cells: the movement of all mesophyll chloroplasts towards bundle sheath cells (aggregative movement) and movement of only those of interveinal mesophyll cells towards bundle sheath cells (avoidance movement). Light absorbed by bundle sheath chloroplasts relative to mesophyll chloroplasts increased in both cases. Avoidance movement decreased light absorption by mesophyll chloroplasts considerably. Consequently, total ATP and NADPH production and net photosynthetic rate increased for aggregative movement and decreased for avoidance movement compared with the default case of no chloroplast movement at high light intensities. Leakiness increased in both chloroplast movement scenarios due to the imbalance in energy production and demand in mesophyll and bundle sheath cells. These results suggest the need to design strategies for coordinated increases in electron transport and Rubisco activities for an efficient CO2 concentrating mechanism at very high light intensities. [ABSTRACT FROM AUTHOR]

Computational tools that allow in silico analysis of the role of cell growth and division on photosynthesis are scarce. We present a freely available tool that combines a virtual leaf tissue generator and a two-dimensional microscale model of gas transport during C3 photosynthesis. A total of 270 mesophyll geometries were generated with varying degrees of growth anisotropy, growth extent, and extent of schizogenous airspace formation in the palisade mesophyll. The anatomical properties of the virtual leaf tissue and microscopic cross-sections of actual leaf tissue of tomato (Solanum lycopersicum L.) were statistically compared. Model equations for transport of CO2 in the liquid phase of the leaf tissue were discretized over the geometries. The virtual leaf tissue generator produced a leaf anatomy of tomato that was statistically similar to real tomato leaf tissue. The response of photosynthesis to intercellular CO2 predicted by a model that used the virtual leaf tissue geometry compared well with measured values. The results indicate that the light-saturated rate of photosynthesis was influenced by interactive effects of extent and directionality of cell growth and degree of airspace formation through the exposed surface of mesophyll per leaf area. The tool could be used further in investigations of improving photosynthesis and gas exchange in relation to cell growth and leaf anatomy. [ABSTRACT FROM AUTHOR]

Summary: Methods using gas exchange measurements to estimate respiration in the light (day respiration Rd) make implicit assumptions about reassimilation of (photo)respired CO2; however, this reassimilation depends on the positions of mitochondria.We used a reaction‐diffusion model without making these assumptions to analyse datasets on gas exchange, chlorophyll fluorescence and anatomy for tomato leaves. We investigated how Rd values obtained by the Kok and the Yin methods are affected by these assumptions and how those by the Laisk method are affected by the positions of mitochondria.The Kok method always underestimated Rd. Estimates of Rd by the Yin method and by the reaction‐diffusion model agreed only for nonphotorespiratory conditions. Both the Yin and Kok methods ignore reassimilation of (photo)respired CO2, and thus underestimated Rd for photorespiratory conditions, but this was less so in the Yin than in the Kok method. Estimates by the Laisk method were affected by assumed positions of mitochondria. It did not work if mitochondria were in the cytosol between the plasmamembrane and the chloroplast envelope. However, mitochondria were found to be most likely between the tonoplast and chloroplasts.Our reaction‐diffusion model effectively estimates Rd, enlightens the dependence of Rd estimates on reassimilation and clarifies (dis)advantages of existing methods. [ABSTRACT FROM AUTHOR]

The CO 2 concentration near Rubisco and, therefore, the rate of CO 2 assimilation, is influenced by both leaf anatomical factors and biochemical processes. Leaf anatomical structures act as physical barriers for CO 2 transport. Biochemical processes add or remove CO 2 along its diffusion pathway through mesophyll. We combined a model that quantifies the diffusive resistance for CO 2 using anatomical properties, a model that partitions this resistance and an extended version of the Farquhar–von Caemmerer–Berry model. We parametrized the model by gas exchange, chlorophyll fluorescence and leaf anatomical measurements from three tomato cultivars. There was generally a good agreement between the predicted and measured light and CO 2 response curves. We did a sensitivity analysis to assess how the rate of CO 2 assimilation responds to changes in various leaf anatomical properties. Next, we conducted a similar analysis for assumed diffusive properties and curvature factors. Some variables (diffusion pathway length in stroma, diffusion coefficient of the stroma, curvature factors) substantially affected the predicted CO 2 assimilation. We recommend more research on the measurements of these variables and on the development of 2-D and 3-D gas diffusion models, since these do not require the diffusion pathway length in the stroma as predefined parameter. [ABSTRACT FROM AUTHOR]