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Structural properties of rice leaves grown under ambient and elevated CO2 levels. (a–d) whole leaf properties of mesophyll thickness at (a) minor vein; (b) bulliform cells; and (c) interveinal distance; (d) mesophyll porosity. (e–h) Mesophyll cell (MC) properties of length (e); width (f); volume (g); and exposed mesophyll surface area, Smes (h). (i, j) Bundle sheath (BS), cell area (i) and sheath thickness (j). (k, l) Percentage of cell occupied by plastids for (k) BS cells and (l) MCs. Bars, mean values; error bars, SEM; n > 5, for mature leaf 5 from rice plants grown under ambient, 480 ppm CO2 (aCO2) or elevated, 1000 ppm CO2 (eCO2). Pairwise t‐tests were performed, with differences indicated when P < 0.05.
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Leaf structure plays an important role in photosynthesis. However, the causal relationship and the quantitative importance of any single structural parameter to the overall photosynthetic performance of a leaf remains open to debate. In this paper, we report on a mechanistic model, eLeaf, which successfully captures rice leaf photosynthetic perform...
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Citations
... Bundle sheath cells and cell-specific plastid development Kinsman and Pyke (1998) Maize Differential sensitivity of chloroplasts in mesophyll and bundle sheath cells an NADP-malic enzyme-type C 4 plant to salinity Stress Hasan et al. (2005) Rice Theoretical analysis of anatomical factors towards C 4 photosynthesis Wang et al. (2017) Rice Modelling towards altering rice leaf anatomy to improve photosynthesis Xiao et al. (2023) Reduce the vein spacing to increase the vein density in the leaf rice Rice Multi-model studies of leaf anatomical traits and vein architecture Narawatthana et al. (2023) Wheat Reduction of photosynthesis under P deficiency is mainly caused by the decreased CO 2 diffusional capacities Shu et al. (2023) Maize Accurate phenotypic identification and genetic analysis of the ear leaf veins Guo et al. (2023) Reduce the calvin cycle activity in mesophyll cell and enhance in bundle sheath cell C 3 and C 4 plants Differential control of the Calvin cycle in C 3 versus C 4 plants Burgess and Wang (2023) Maize Compartmentation of photosynthesis gene expression between mesophyll and bundle sheath cells of C 4 maize is dependent on time of day Borba et al. (2023) Reduce the photorespiration in mesophyll cells Rice Identification of lowered photorespiration and respiration rat Mubarak et al. (2023) Maize Chromatin and regulatory differentiation between bundle sheath and mesophyll cells Dai et al. (2022) Improving the quality and quantity of Rubisco Rice Breeding effects in conversion of c3 rice plant to c4 ...
Crop yields must drastically increase to meet the demands of a rapidly increasing global population. One current option being investigated is the augmentation of photosynthetic capacity by incorporating the C4 photosynthetic pathway into C3 crops such as rice to significantly increase production. Crops with improved photosynthetic mechanisms would make better use of the solar radiation that can be converted into yield. This will help to boost grain yield, reduce water loss, and increase nitrogen use efficiency, particularly in hot and dry conditions. Identifying and manipulating the genes required to install C4 photosynthesis in rice is a big challenge. However, the international C4 rice collaboration, is formed to test the possibility of incorporating the C4 mechanism into rice. This article summarizes the parameters that must be changed in rice in order for the C4 pathway to be successfully introduced. It also examines the biochemistry, physiology, molecular biology, and synthetic biology approaches between the C3 and C4 photosynthetic processes.
... Cell projection images were created using an in-house FIJI macro -each cell was orientated so that the 0 line was horizontal, and then cell outlines were superimposed. For IR64 With the constructed leaf architecture, light propagation inside the leaf was simulated by a Monte-Carlo ray tracing algorithm (Govaerts et al., 1996;Xiao et al., 2016Xiao et al., , 2023. Due to the lack of epidermal cells in these simplified models, diffuse incident rays were emitted onto the upper boundary as the light source. ...
... CO 2 reaction and diffusion inside the leaf were simulated by a partial differential system(Tholen & Zhu, 2011;Xiao et al., 2023; F I G U R E 1 Cell layers in the mesophyll of rice IR64 can be distinguished by size, shape, and orientation. (a) Representation of rice mesophyll with different cell layers highlighted from Layer 1 (touching the adaxial epidermis) to Layer 5 (touching the abaxial epidermis). ...
The mesophyll cells of grass leaves, such as rice, are traditionally viewed as displaying a relatively uniform pattern, in contrast to the clear distinctions of palisade and spongy layers in typical eudicot leaves. This quantitative analysis of mesophyll cell size and shape in rice leaves reveals that there is an inherent pattern in which cells in the middle layer of the mesophyll are larger and less circular and have a distinct orientation of their long axis compared to mesophyll cells in other layers. Moreover, this pattern was observed in a range of rice cultivars and species. The significance of this pattern with relation to potential photosynthetic function and the implication of the widespread use of middle layer mesophyll cells as typical of the rice leaf have been investigated and discussed.
... Second, chloroplast size may also affect leaf light absorption characteristics. Light attenuation is an important component of photosynthetic efficiency, and theoretically, a uniform distribution of light across all chloroplasts is optimal for photosynthetic efficiency because of the hyperbolic shape of the photosynthetic light response (Xiao et al., 2023). Lower transmission was observed for leaves of chloroplast mutant lines with large chloroplasts (Jeong et al., 2002;Königer et al., 2008), but it is currently unclear to what extent this was caused specifically by size alterations or instead by concomitant reductions in chlorophyll content and chla : chlb ratio. ...
Improving photosynthetic efficiency has recently emerged as a promising way to increase crop production in a sustainable manner. While chloroplast size may affect photosynthetic efficiency in several ways, we aimed to explore whether chloroplast size manipulation can be a viable approach to improving photosynthetic performance.
Several tobacco (Nicotiana tabacum) lines with contrasting chloroplast sizes were generated via manipulation of chloroplast division genes to assess photosynthetic performance under steady‐state and fluctuating light. A selection of lines was included in a field trial to explore productivity.
Lines with enlarged chloroplasts underperformed in most of the measured traits. Lines with smaller and more numerous chloroplasts showed a similar efficiency compared with wild‐type (WT) tobacco. Chloroplast size only weakly affected light absorptance and light profiles within the leaf. Increasing chloroplast size decreased mesophyll conductance (gm) but decreased chloroplast size did not increase gm. Increasing chloroplast size reduced chloroplast movements and enhanced non‐photochemical quenching. The chloroplast smaller than WT appeared to be no better than WT for photosynthetic efficiency and productivity under field conditions.
The results indicate that chloroplast size manipulations are therefore unlikely to lead to higher photosynthetic efficiency or growth.
... As such, research efforts that contribute to the advancement of a 'virtual leaf' need to be assessed in terms of how they improve our limited understanding of plant physiology, not how they fail to capture complex reality. Xiao et al. (2022) exemplify an excellent approach to creating a 'virtual leaf'. The authors use different microscopy modalities (micro-CT, confocal and transmission electron microscopy) to capture leaf anatomy at different spatial scales. ...
... The authors validated their modelling assumptions with experimental data and termed the final product 'eLeaf'. Xiao et al. (2022) utilized 'eLeaf' to discover that changing leaf porosity had little influence on photosynthetic performance which aligns with the observations from Theroux- that cell size is much more important than porosity. It is worth noting that Theroux- took 3D anatomical data to estimate 2D CO 2 diffusion and Xiao et al. (2022) took 2D anatomical data to estimate 3D diffusion. ...
... Xiao et al. (2022) utilized 'eLeaf' to discover that changing leaf porosity had little influence on photosynthetic performance which aligns with the observations from Theroux- that cell size is much more important than porosity. It is worth noting that Theroux- took 3D anatomical data to estimate 2D CO 2 diffusion and Xiao et al. (2022) took 2D anatomical data to estimate 3D diffusion. As 3D modelling approaches evolve, we will gain a better understanding of what level of detail is needed to answer specific research questions. ...
When microscopy meets modelling the exciting concept of a ‘virtual leaf’ is born. The goal of a ‘virtual leaf’ is to capture complex physiology in a virtual environment, resulting in the capacity to run experiments computationally. One example of a ‘virtual leaf’ application is capturing 3D anatomy from volume microscopy data and estimating where water evaporates in the leaf and the proportions of apoplastic, symplastic and gas phase water transport. The same 3D anatomy could then be used to improve established 3D reaction-diffusion models, providing a better understanding of the transport of CO2 across the stomata, through the airspace and across the mesophyll cell wall. This viewpoint discusses recent progress that has been made in transitioning from a bulk leaf approach to a 3D understanding of leaf physiology, in particular, the movement of CO2 and H2O within the leaf.
To explore the internal factors related to the strong growth and competitive ability of weedy rice during the seedling period, we collected two biotypes of Japonica weedy rice from Northeast China, four biotypes of Indica weedy rice from Eastern China and Southern China, and two biotypes of cultivated rice, Zhendao-8 (ZD-8) and Shanyou-63 (SY-63), which were used as controls in a pot experiment. Under homogeneous garden planting conditions, we measured the vascular bundle size (VBS), vascular bundle number (VBN), leaf thickness (LT), air cavity size (ACS), stomatal size (SS), stomatal density (SD), net photosynthetic rate (Pn) and stomatal conductance (Gs) of the weedy and cultivated rice biotypes. A comprehensive analysis was performed to explore the correlation between the seedling leaf structure and the photosynthetic indices of the biotypes. The results showed the following: (1) At the seedling growth stage, the leaf structure parameters of weedy rice were significantly greater than those of ZD-8 and SY-63. (2) The Pn and Gs of weedy rice were significantly positively correlated with VBS, VBN, LT, ACS, and SD. Thus, the leaf structural features of weedy rice provide the anatomical basis for the stronger Pn and establish a strong competitive physiology at the seedling stage. Therefore, the prevention and elimination of weedy rice should start at the seedling stage.
The growing demand for global food production is likely to be a defining issue facing humanity over the next 50 years. To tackle this challenge, there is a desire to bioengineer crops with higher photosynthetic efficiencies, to increase yields. Recently, there has been a growing interest in engineering leaves with higher mesophyll conductance ( g m ), which would allow CO 2 to move more efficiently from the substomatal cavities to the chloroplast stroma. However, if crop yield gains are to be realised through this approach, it is essential that the methodological limitations associated with estimating g m are fully appreciated. In this review, we summarise these limitations, and outline the uncertainties and assumptions that can affect the final estimation of g m . Furthermore, we critically assess the predicted quantitative effect that elevating g m will have on assimilation rates in crop species. We highlight the need for more theoretical modelling to determine whether altering g m is truly a viable route to improve crop performance. Finally, we offer suggestions to guide future research on g m , which will help mitigate the uncertainty inherently associated with estimating this parameter.
Improving photosynthesis, the fundamental process by which plants convert light energy into chemical energy, is a key area of research with great potential for enhancing sustainable agricultural productivity and addressing global food security challenges. This perspective delves into the latest advancements and approaches aimed at optimizing photosynthetic efficiency. Our discussion encompasses the entire process, beginning with light harvesting and its regulation and progressing through the bottleneck of electron transfer. We then delve into the carbon reactions of photosynthesis, focusing on strategies targeting the enzymes of the Calvin-Benson-Bassham (CBB) cycle. Additionally, we explore methods to increase CO2 concentration near the Rubisco, the enzyme responsible for the first step of CBB cycle, drawing inspiration from various photosynthetic organisms, and conclude this section by examining ways to enhance CO2 delivery into leaves. Moving beyond individual processes, we discuss two approaches to identifying key targets for photosynthesis improvement: systems modeling and the study of natural variation. Finally, we revisit some of the strategies mentioned above to provide a holistic view of the improvements, analyzing their impact on nitrogen use efficiency and on canopy photosynthesis.
The microphenotype plays a key role in bridging the gap between the genotype and the complex macro phenotype. In this article, we review the advances in data acquisition and the intelligent analysis of plant microphenotyping and present applications of microphenotyping in plant science over the past two decades. We then point out several challenges in this field and suggest that cross‐scale image acquisition strategies, powerful artificial intelligence algorithms, advanced genetic analysis, and computational phenotyping need to be established and performed to better understand interactions among genotype, environment, and management. Microphenotyping has entered the era of Microphenotyping 3.0 and will largely advance functional genomics and plant science.
The growing demand for global food production is likely to be a defining issue facing humanity over the next 50 years. In order to tackle this challenge, there is a desire to bioengineer crops with higher photosynthetic efficiencies, to increase yields. Recently, there has been a growing interest in engineering leaves with higher mesophyll conductance ( g ), which would allow CO to move more efficiently from the substomatal cavities to the chloroplast stroma. However, if crop yield gains are to be realised through this approach, it is essential that the methodological limitations associated with estimating gm are fully appreciated. In this review, we summarise these limitations, and outline the uncertainties and assumptions that can affect the final estimation of g . Furthermore, we critically assess the predicted quantitative effect that elevating g will have on assimilation rates in crop species. We highlight the need for more theoretical modelling to determine whether altering g is truly a viable route to improve crop performance. Finally, we offer suggestions to guide future research on g , which will help mitigate the uncertainty inherently associated with estimating this parameter.
