RESUMO
Understanding the short-term responses of mesophyll conductance (gm) and stomatal conductance (gsc) to environmental changes remains a challenging yet central aspect of plant physiology. This review synthesises our current knowledge of these short-term responses, which underpin CO2 diffusion within leaves. Recent methodological advances in measuring gm using online isotopic discrimination and chlorophyll fluorescence have improved our confidence in detecting short-term gm responses, but results need to be carefully evaluated. Environmental factors like vapour pressure deficit and CO2 concentration indirectly impact gm through gsc changes, highlighting some of the complex interactions between the two parameters. Evidence suggests that short-term responses of gm are not, or at least not fully, mechanistically linked to changes in gsc, cautioning against using gsc as a reliable proxy for gm. The overarching challenge lies in unravelling the mechanistic basis of short-term gm responses, which will contribute to the development of accurate models bridging laboratory insights with broader ecological implications. Addressing these gaps in understanding is crucial for refining predictions of gm behaviour under changing environmental conditions.
Assuntos
Células do Mesofilo , Estômatos de Plantas , Células do Mesofilo/fisiologia , Células do Mesofilo/metabolismo , Estômatos de Plantas/fisiologia , Dióxido de Carbono/metabolismo , Meio Ambiente , Folhas de Planta/fisiologia , Folhas de Planta/metabolismo , Transpiração Vegetal/fisiologiaRESUMO
C2 photosynthesis is a photosynthetic pathway in which photorespiratory CO2 release and refixation are enhanced in leaf bundle sheath (BS) tissues. The evolution of C2 photosynthesis has been hypothesized to be a major step in the origin of C4 photosynthesis, highlighting the importance of studying C2 evolution. In this study, physiological, anatomical, ultrastructural, and immunohistochemical properties of leaf photosynthetic tissues were investigated in six non-C4 Tribulus species and four C4 Tribulus species. At 42°C, T. cristatus exhibited a photosynthetic CO2 compensation point in the absence of respiration (C*) of 21 µmol mol-1, below the C3 mean C* of 73 µmol mol-1. Tribulus astrocarpus had a C* value at 42°C of 55 µmol mol-1, intermediate between the C3 species and the C2 T. cristatus. Glycine decarboxylase (GDC) allocation to BS tissues was associated with lower C*. Tribulus cristatus and T. astrocarpus allocated 86% and 30% of their GDC to the BS tissues, respectively, well above the C3 mean of 11%. Tribulus astrocarpus thus exhibits a weaker C2 (termed sub-C2) phenotype. Increased allocation of mitochondria to the BS and decreased length-to-width ratios of BS cells, were present in non-C4 species, indicating a potential role in C2 and C4 evolution.
Assuntos
Evolução Biológica , Fotossíntese , Folhas de Planta , Fotossíntese/fisiologia , Folhas de Planta/fisiologia , Folhas de Planta/metabolismo , Dióxido de Carbono/metabolismo , Glicina Desidrogenase (Descarboxilante)/metabolismoRESUMO
Gas exchange measurements enable mechanistic insights into the processes that underpin carbon and water fluxes in plant leaves which in turn inform understanding of related processes at a range of scales from individual cells to entire ecosytems. Given the importance of photosynthesis for the global climate discussion it is important to (a) foster a basic understanding of the fundamental principles underpinning the experimental methods used by the broad community, and (b) ensure best practice and correct data interpretation within the research community. In this review, we outline the biochemical and biophysical parameters of photosynthesis that can be investigated with gas exchange measurements and we provide step-by-step guidance on how to reliably measure them. We advise on best practices for using gas exchange equipment and highlight potential pitfalls in experimental design and data interpretation. The Supporting Information contains exemplary data sets, experimental protocols and data-modelling routines. This review is a community effort to equip both the experimental researcher and the data modeller with a solid understanding of the theoretical basis of gas-exchange measurements, the rationale behind different experimental protocols and the approaches to data interpretation.
Assuntos
Fotossíntese , Fotossíntese/fisiologia , Folhas de Planta/fisiologia , Folhas de Planta/metabolismo , Dióxido de Carbono/metabolismo , Plantas/metabolismoRESUMO
Photosynthetic manipulation provides new opportunities for enhancing crop yield. However, understanding and quantifying the importance of individual and multiple manipulations on the seasonal biomass growth and yield performance of target crops across variable production environments is limited. Using a state-of-the-art cross-scale model in the APSIM platform we predicted the impact of altering photosynthesis on the enzyme-limited (Ac ) and electron transport-limited (Aj ) rates, seasonal dynamics in canopy photosynthesis, biomass growth, and yield formation via large multiyear-by-location crop growth simulations. A broad list of promising strategies to improve photosynthesis for C3 wheat and C4 sorghum were simulated. In the top decile of seasonal outcomes, yield gains were predicted to be modest, ranging between 0% and 8%, depending on the manipulation and crop type. We report how photosynthetic enhancement can affect the timing and severity of water and nitrogen stress on the growing crop, resulting in nonintuitive seasonal crop dynamics and yield outcomes. We predicted that strategies enhancing Ac alone generate more consistent but smaller yield gains across all water and nitrogen environments, Aj enhancement alone generates larger gains but is undesirable in more marginal environments. Large increases in both Ac and Aj generate the highest gains across all environments. Yield outcomes of the tested manipulation strategies were predicted and compared for realistic Australian wheat and sorghum production. This study uniquely unpacks complex cross-scale interactions between photosynthesis and seasonal crop dynamics and improves understanding and quantification of the potential impact of photosynthesis traits (or lack of it) for crop improvement research.
Assuntos
Nitrogênio , Água , AustráliaRESUMO
Cuticular conductance to water (gcw ) is difficult to quantify for stomatous surfaces due to the complexity of separating cuticular and stomatal transpiration, and additional complications arise for determining adaxial and abaxial gcw . This has led to the neglect of gcw as a separate parameter in most common gas exchange measurements. Here, we describe a simple technique to simultaneously estimate adaxial and abaxial values of gcw , tested in two amphistomatous plant species. What we term the 'Red-Light method' is used to estimate gcw from gas exchange measurements and a known CO2 concentration inside the leaf during photosynthetic induction under red light. We provide an easy-to-use web application to assist with the calculation of gcw . While adaxial and abaxial gcw varies significantly between leaves of the same species we found that the ratio of adaxial/abaxial gcw (γn ) is stable within a plant species. This has implications for use of generic values of gcw when analysing gas exchange data. The Red-Light method can be used to estimate total cuticular conductance (gcw-T ) accurately with the most common setup of gas exchange instruments, i.e. a chamber mixing the adaxial and abaxial gases, allowing for a wide application of this technique.
Assuntos
Fotossíntese , Folhas de Planta , Luz , ÁguaRESUMO
Photorespiratory metabolism is essential for plants to maintain functional photosynthesis in an oxygen-containing environment. Because the oxygenation reaction of Rubisco is followed by the loss of previously fixed carbon, photorespiration is often considered a wasteful process and considerable efforts are aimed at minimizing the negative impact of photorespiration on the plant's carbon uptake. However, the photorespiratory pathway has also many positive aspects, as it is well integrated within other metabolic processes, such as nitrogen assimilation and C1 metabolism, and it is important for maintaining the redox balance of the plant. The overall effect of photorespiratory carbon loss on the net CO2 fixation of the plant is also strongly influenced by the physiology of the leaf related to CO2 diffusion. This review outlines the distinction between Rubisco oxygenation and photorespiratory CO2 release as a basis to evaluate the costs and benefits of photorespiration.
Assuntos
Dióxido de Carbono/metabolismo , Plantas/metabolismo , Ribulose-Bifosfato Carboxilase/metabolismo , Cloroplastos/metabolismo , Glicina/metabolismo , Redes e Vias Metabólicas , Nitrogênio/metabolismo , Oxigênio/metabolismo , Fotossíntese/fisiologia , Folhas de Planta/metabolismo , Proteínas de Plantas/química , Proteínas de Plantas/metabolismo , Ribulose-Bifosfato Carboxilase/química , Enxofre/metabolismoRESUMO
Bundle Sheath Defective 2, BSD2, is a stroma-targeted protein initially identified as a factor required for the biogenesis of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) in maize. Plants and algae universally have a homologous gene for BSD2 and its deficiency causes a RuBisCO-less phenotype. As RuBisCO can be the rate-limiting step in CO2 assimilation, the overexpression of BSD2 might improve photosynthesis and productivity through the accumulation of RuBisCO. To examine this hypothesis, we produced BSD2 overexpression lines in Arabidopsis. Compared with wild type, the BSD2 overexpression lines BSD2ox-2 and BSD2ox-3 expressed 4.8-fold and 8.8-fold higher BSD2 mRNA, respectively, whereas the empty-vector (EV) harbouring plants had a comparable expression level. The overexpression lines showed a significantly higher CO2 assimilation rate per available CO2 and productivity than EV plants. The maximum carboxylation rate per total catalytic site was accelerated in the overexpression lines, while the number of total catalytic sites and RuBisCO content were unaffected. We then isolated recombinant BSD2 (rBSD2) from E. coli and found that rBSD2 reduces disulfide bonds using reductants present in vivo, for example glutathione, and that rBSD2 has the ability to reactivate RuBisCO that has been inactivated by oxidants. Furthermore, 15% of RuBisCO freshly isolated from leaves of EV was oxidatively inactivated, as compared with 0% in BSD2-overexpression lines, suggesting that the overexpression of BSD2 maintains RuBisCO to be in the reduced active form in vivo. Our results demonstrated that the overexpression of BSD2 improves photosynthetic efficiency in Arabidopsis and we conclude that it is involved in mediating RuBisCO activation.
Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Fotossíntese/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Arabidopsis/fisiologia , Proteínas de Arabidopsis/metabolismo , Proteínas de Arabidopsis/fisiologia , Escherichia coli , Regulação da Expressão Gênica de Plantas , Proteínas Recombinantes , Ribulose-Bifosfato Carboxilase/metabolismoRESUMO
The Australian grass subtribe Neurachninae contains closely related species that use C3, C4, and C2 photosynthesis. To gain insight into the evolution of C4 photosynthesis in grasses, we examined leaf gas exchange, anatomy and ultrastructure, and tissue localization of Gly decarboxylase subunit P (GLDP) in nine Neurachninae species. We identified previously unrecognized variation in leaf structure and physiology within Neurachne that represents varying degrees of C3-C4 intermediacy in the Neurachninae. These include inverse correlations between the apparent photosynthetic carbon dioxide (CO2) compensation point in the absence of day respiration (C * ) and chloroplast and mitochondrial investment in the mestome sheath (MS), where CO2 is concentrated in C2 and C4 Neurachne species; width of the MS cells; frequency of plasmodesmata in the MS cell walls adjoining the parenchymatous bundle sheath; and the proportion of leaf GLDP invested in the MS tissue. Less than 12% of the leaf GLDP was allocated to the MS of completely C3 Neurachninae species with C * values of 56-61 µmol mol-1, whereas two-thirds of leaf GLDP was in the MS of Neurachne lanigera, which exhibits a newly-identified, partial C2 phenotype with C * of 44 µmol mol-1 Increased investment of GLDP in MS tissue of the C2 species was attributed to more MS mitochondria and less GLDP in mesophyll mitochondria. These results are consistent with a model where C4 evolution in Neurachninae initially occurred via an increase in organelle and GLDP content in MS cells, which generated a sink for photorespired CO2 in MS tissues.
Assuntos
Folhas de Planta/metabolismo , Proteínas de Plantas/metabolismo , Fotossíntese/genética , Fotossíntese/fisiologia , Folhas de Planta/fisiologia , Proteínas de Plantas/genética , Plasmodesmos/metabolismo , Plasmodesmos/fisiologia , Poaceae/genética , Poaceae/fisiologiaRESUMO
On the occasion of the 40th anniversary of the publication of the landmark model by Farquhar, von Caemmerer & Berry on steady-state C3 photosynthesis (known as the "FvCB model"), we review three major further developments of the model. These include: (1) limitation by triose phosphate utilization, (2) alternative electron transport pathways, and (3) photorespiration-associated nitrogen and C1 metabolisms. We discussed the relation of the third extension with the two other extensions, and some equivalent extensions to model C4 photosynthesis. In addition, the FvCB model has been coupled with CO2 -diffusion models. We review how these extensions and integration have broadened the use of the FvCB model in understanding photosynthesis, especially with regard to bioenergetic stoichiometries associated with photosynthetic quantum yields. Based on the new insights, we present caveats in applying the FvCB model. Further research needs are highlighted.
Assuntos
Modelos Biológicos , Fotossíntese , Transporte de Elétrons , Redes e Vias Metabólicas , Plantas/metabolismoRESUMO
C4 plants, such as maize, strictly compartmentalize Rubisco to bundle sheath chloroplasts. The molecular basis for the restriction of Rubisco from the more abundant mesophyll chloroplasts is not fully understood. Mesophyll chloroplasts transcribe the Rubisco large subunit gene and, when normally quiescent transcription of the nuclear Rubisco small subunit gene family is overcome by ectopic expression, mesophyll chloroplasts still do not accumulate measurable Rubisco. Here we show that a combination of five ubiquitin promoter-driven nuclear transgenes expressed in maize leads to mesophyll accumulation of assembled Rubisco. These encode the Rubisco large and small subunits, Rubisco assembly factors 1 and 2, and the assembly factor Bundle sheath defective 2. In these plants, Rubisco large subunit accumulates in mesophyll cells, and appears to be assembled into a holoenzyme capable of binding the substrate analog CABP (carboxyarabinitol bisphosphate). Isotope discrimination assays suggest, however, that mesophyll Rubisco is not participating in carbon assimilation in these plants, most probably due to a lack of the substrate ribulose 1,5-bisphosphate and/or Rubisco activase. Overall, this work defines a minimal set of Rubisco assembly factors in planta and may help lead to methods of regulating the C4 pathway.
Assuntos
Ribulose-Bifosfato Carboxilase , Zea mays , Cloroplastos/metabolismo , Expressão Ectópica do Gene , Células do Mesofilo/metabolismo , Fotossíntese , Ribulose-Bifosfato Carboxilase/genética , Ribulose-Bifosfato Carboxilase/metabolismo , Zea mays/genética , Zea mays/metabolismoRESUMO
Many C4 plants, including maize, perform poorly under chilling conditions. This phenomenon has been linked in part to decreased Rubisco abundance at lower temperatures. An exception to this is chilling-tolerant Miscanthus, which is able to maintain Rubisco protein content under such conditions. The goal of this study was to investigate whether increasing Rubisco content in maize could improve performance during or following chilling stress. Here, we demonstrate that transgenic lines overexpressing Rubisco large and small subunits and the Rubisco assembly factor RAF1 (RAF1-LSSS), which have increased Rubisco content and growth under control conditions, maintain increased Rubisco content and growth during chilling stress. RAF1-LSSS plants exhibited 12% higher CO2 assimilation relative to nontransgenic controls under control growth conditions, and a 17% differential after 2 weeks of chilling stress, although assimilation rates of all genotypes were ~50% lower in chilling conditions. Chlorophyll fluorescence measurements showed RAF1-LSSS and WT plants had similar rates of photochemical quenching during chilling, suggesting Rubisco may not be the primary limiting factor that leads to poor performance in maize under chilling conditions. In contrast, RAF1-LSSS had improved photochemical quenching before and after chilling stress, suggesting that increased Rubisco may help plants recover faster from chilling conditions. Relatively increased leaf area, dry weight and plant height observed before chilling in RAF1-LSSS were also maintained during chilling. Together, these results demonstrate that an increase in Rubisco content allows maize plants to better cope with chilling stress and also improves their subsequent recovery, yet additional modifications are required to engineer chilling tolerance in maize.
Assuntos
Ribulose-Bifosfato Carboxilase , Zea mays , Temperatura Baixa , Fotossíntese , Poaceae/metabolismo , Ribulose-Bifosfato Carboxilase/metabolismo , Zea mays/genética , Zea mays/metabolismoRESUMO
More efficient gas exchange strategies under dynamic light environments have been hypothesised to contribute to the dominance of angiosperms in the vascular plant flora. However, we still lack a clear understanding of how stomatal dynamics affect photosynthetic dynamics and whether differences exist between lineages. Stomatal and photosynthetic dynamics following changes in irradiance were studied in 15 species, encompassing ferns, gymnosperms and angiosperms. We determined the effect of stomatal speed on dynamic photosynthesis and water loss. Moreover, we assessed whether dynamic behaviour followed evolutionary lineage divisions, or whether ecological adaptation to maximise light fleck use could describe dynamic behaviour. We found that species with fast stomatal opening, such as ferns, forgo less photosynthesis during photosynthetic induction. By contrast, there was no relationship between stomatal closure speed and the water wasted by transiently more-open stomata, because species with higher rates of gas exchange also showed faster stomatal closure. Shade-adapted species possessed fast-opening but slow-closing stomata, consistent with ecological adaptation to maximise light fleck use. Our results suggest dynamic behaviour follows adaptive ecological trends more strongly than evolutionary ones, but angiosperms may benefit from relatively faster photosynthetic induction by adopting a less conservative water-use strategy.
Assuntos
Luz , Fotossíntese/efeitos da radiação , Estômatos de Plantas/fisiologia , Estômatos de Plantas/efeitos da radiação , Água/metabolismo , Adaptação Fisiológica/efeitos da radiação , Gases/metabolismo , Fatores de TempoRESUMO
The arrangement of mitochondria and chloroplasts, together with the relative resistances of cell wall and chloroplast, determine the path of diffusion out of the leaf for (photo)respired CO2. Traditional photosynthesis models have assumed a tight arrangement of chloroplasts packed together against the cell wall with mitochondria located behind the chloroplasts, deep inside the cytosol. Accordingly, all (photo)respired CO2 must cross the chloroplast before diffusing out of the leaf. Different arrangements have recently been considered, where all or part of the (photo)respired CO2 diffuses through the cytosol without ever entering the chloroplast. Assumptions about the path for the (photo)respiratory flux are particularly relevant for the calculation of mesophyll conductance (gm). If (photo)respired CO2 can diffuse elsewhere besides the chloroplast, apparent gm is no longer a mere physical resistance but a flux-weighted variable sensitive to the ratio of (photo)respiration to net CO2 assimilation. We discuss existing photosynthesis models in conjunction with their treatment of the (photo)respiratory flux and present new equations applicable to the generalized case where (photo)respired CO2 can diffuse both into the chloroplast and through the cytosol. Additionally, we present a new generalized Δ13C model that incorporates this dual diffusion pathway. We assess how assumptions about the fate of (photo)respired CO2 affect the interpretation of photosynthetic data and the challenges it poses for the application of different models.
Assuntos
Isótopos de Carbono/metabolismo , Cloroplastos/metabolismo , Mitocôndrias/metabolismo , Modelos Biológicos , Fotossíntese , Células do Mesofilo/metabolismoRESUMO
Understanding stomatal and biochemical components that limit photosynthesis under different conditions is important for both the targeted improvement of photosynthesis and the elucidation of how stomata and biochemistry affect plant performance in an ecological context. Limitation analyses have not yet been extensively applied to conditions of photosynthetic induction after an increase in irradiance. Moreover, few studies have systematically assessed how well various limitation analyses actually work. Here we build on two general ways of estimating limitations, one that sequentially removes the effect of a limitation (elimination) and one that uses a tangent plane approximation (differential), by including the ternary effect and boundary layer conductance so that they are consistent with gas exchange data. We apply them to the analysis of temporal and time-integrated limitations during photosynthetic induction, calculating limitations either independent of the time course (one-step) or make use of the entire time course (stepwise). We show that the stepwise differential method is the best method to use when time steps are small enough. We further show that the differential method predicts limitations near exact when the internal CO2 concentration stays constant. This last insight has important implications for the general use of limitation analyses beyond photosynthetic induction.
Assuntos
Fotossíntese/fisiologia , Estômatos de Plantas/fisiologia , Gleiquênias/fisiologia , Modelos Biológicos , Fatores de TempoRESUMO
Mitochondrial respiration often appears to be inhibited in the light when compared with measurements in the dark. This inhibition is inferred from the response of the net CO2 assimilation rate (A) to absorbed irradiance (I), changing slope around the light compensation point (Ic ). We suggest a model that provides a plausible mechanistic explanation of this 'Kok effect'. The model uses the mathematical description of photosynthesis developed by Farquhar, von Caemmerer and Berry; it involves no inhibition of respiration rate in the light. We also describe a fitting technique for quantifying the Kok effect at low I. Changes in the chloroplastic CO2 partial pressure (Cc ) can explain curvature of A vs I, its diminution in C4 plants and at low oxygen concentrations or high carbon dioxide concentrations in C3 plants, and effects of dark respiration rate and of temperature. It also explains the apparent inhibition of respiration in the light as inferred by the Laisk approach. While there are probably other sources of curvature in A vs I, variation in Cc can largely explain the curvature at low irradiance, and suggests that interpretation of day respiration compared with dark respiration of leaves on the basis of the Kok effect needs reassessment.
Assuntos
Dióxido de Carbono/metabolismo , Cloroplastos/metabolismo , Modelos Biológicos , Processos Fotoquímicos , Cloroplastos/efeitos dos fármacos , Cloroplastos/efeitos da radiação , Luz , Oxigênio/farmacologia , Pressão Parcial , Fotossíntese/efeitos dos fármacos , Fotossíntese/efeitos da radiação , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismo , Folhas de Planta/efeitos da radiação , TemperaturaRESUMO
The biochemical model of C3 photosynthesis by Farquhar, von Caemmerer and Berry (FvCB) assumes that photosynthetic CO2 assimilation is limited by one of three biochemical processes that are not always easily discerned. This leads to improper assessments of biochemical limitations that limit the accuracy of the model predictions. We use the sensitivity of rates of CO2 assimilation and photosynthetic electron transport to changes in O2 and CO2 concentration in the chloroplast to evaluate photosynthetic limitations. Assessing the sensitivities to O2 and CO2 concentrations reduces the impact of uncertainties in the fixed parameters to a minimum and simultaneously entirely eliminates the need to determine the variable parameters of the model, such as Vcmax , J, or TP . Our analyses demonstrate that Rubisco limits carbon assimilation at high temperatures, while it is limited by triose phosphate utilization at lower temperatures and at higher CO2 concentrations. Measurements can be assigned a priori to one of the three functions of the FvCB model, allowing testing for the suitability of the selected fixed parameters of the model. This approach can improve the reliability of photosynthesis models on scales from the leaf level to estimating the global carbon budget.
Assuntos
Dióxido de Carbono/metabolismo , Ipomoea batatas/fisiologia , Oxigênio/metabolismo , Fotossíntese , Ribulose-Bifosfato Carboxilase/metabolismo , Temperatura , Clorofila/metabolismo , Transporte de Elétrons , Modelos Biológicos , Complexo de Proteína do Fotossistema II/metabolismoRESUMO
Contents 986 I. 987 II. 987 III. 988 IV. 991 V. 992 VI. 995 VII. 997 VIII. 998 References 998 SUMMARY: It has been 75 yr since leaf respiratory metabolism in the light (day respiration) was identified as a low-flux metabolic pathway that accompanies photosynthesis. In principle, it provides carbon backbones for nitrogen assimilation and evolves CO2 and thus impacts on plant carbon and nitrogen balances. However, for a long time, uncertainties have remained as to whether techniques used to measure day respiratory efflux were valid and whether day respiration responded to environmental gaseous conditions. In the past few years, significant advances have been made using carbon isotopes, 'omics' analyses and surveys of respiration rates in mesocosms or ecosystems. There is substantial evidence that day respiration should be viewed as a highly dynamic metabolic pathway that interacts with photosynthesis and photorespiration and responds to atmospheric CO2 mole fraction. The view of leaf day respiration as a constant and/or negligible parameter of net carbon exchange is now outdated and it should now be regarded as a central actor of plant carbon-use efficiency.
Assuntos
Dióxido de Carbono/metabolismo , Folhas de Planta/metabolismo , Respiração Celular , Ecossistema , Nitrogênio/metabolismoRESUMO
Biochemical models of leaf photosynthesis, which are essential for understanding the impact of photosynthesis to changing environments, depend on accurate parameterizations. One such parameter, the photorespiratory CO2 compensation point can be measured from the intersection of several CO2 response curves measured under sub-saturating illumination. However, determining the actual intersection while accounting for experimental noise can be challenging. Additionally, leaf photosynthesis model outcomes are sensitive to the diffusion paths of CO2 released from the mitochondria. This diffusion path of CO2 includes both chloroplastic as well as cell wall resistances to CO2 , which are not readily measurable. Both the difficulties of determining the photorespiratory CO2 compensation point and the impact of multiple intercellular resistances to CO2 can be addressed through application of slope-intercept regression. This technical report summarizes an improved framework for implementing slope-intercept regression to evaluate measurements of the photorespiratory CO2 compensation point. This approach extends past work to include the cases of both Rubisco and Ribulose-1,5-bisphosphate (RuBP)-limited photosynthesis. This report further presents two interactive graphical applications and a spreadsheet-based tool to allow users to apply slope-intercept theory to their data.
Assuntos
Dióxido de Carbono/metabolismo , Fotossíntese/fisiologia , Interpretação Estatística de Dados , Modelos Biológicos , Folhas de Planta/metabolismo , Folhas de Planta/fisiologia , Fenômenos Fisiológicos Vegetais , Plantas/metabolismo , SoftwareRESUMO
Photorespiratory glycine shuttling and decarboxylation in bundle sheath (BS) cells exhibited by C2 species is proposed to be the evolutionary bridge to C4 photosynthesis in eudicots. To evaluate this in grasses, we compare anatomy, cellular localization of glycine decarboxylase (GDC), and photosynthetic physiology of a suspected C2 grass, Homolepis aturensis, with these traits in known C2 grasses, Neurachne minor and Steinchisma hians, and C3 S laxum that is sister to S hians We also use publicly available genome and RNA-sequencing data to examine the evolution of GDC subunits and enhance our understanding of the evolution of BS-specific GDC expression in C2 and C4 grasses. Our results confirm the identity of H aturensis as a C2 species; GDC is confined predominantly to the organelle-enriched BS cells in H aturensis and S hians and to mestome sheath cells of N minor Phylogenetic analyses and data obtained from immunodetection of the P-subunit of GDC are consistent with the hypothesis that the BS dominant levels of GDC in C2 and C4 species are due to changes in expression of a single GLDP gene in M and BS cells. All BS mitochondria and peroxisomes and most chloroplasts in H aturensis and S hians are situated centripetally in a pattern identical to C2 eudicots. In S laxum, which has C3-like gas exchange patterns, mitochondria and peroxisomes are positioned centripetally as they are in S hians This subcellular phenotype, also present in eudicots, is posited to initiate a facilitation cascade leading to C2 and C4 photosynthesis.
Assuntos
Glicina Desidrogenase (Descarboxilante)/metabolismo , Fotossíntese/fisiologia , Poaceae/fisiologia , Evolução Biológica , Genes de Plantas/genética , Genes de Plantas/fisiologia , Glicina Desidrogenase (Descarboxilante)/genética , Filogenia , Folhas de Planta/anatomia & histologia , Folhas de Planta/citologia , Folhas de Planta/fisiologia , Poaceae/citologia , Poaceae/enzimologia , Poaceae/metabolismo , Ribulose-Bifosfato Carboxilase/metabolismoRESUMO
Recycling of the 2-phosphoglycolate generated by the oxygenase reaction of Rubisco requires a complex and energy-consuming set of reactions collectively known as the photorespiratory cycle. Several approaches aimed at reducing the rates of photorespiratory energy or carbon loss have been proposed, based either on screening for natural variation or by means of genetic engineering. Recent work indicates that plant yield can be substantially improved by the alteration of photorespiratory fluxes or by engineering artificial bypasses to photorespiration. However, there is also evidence indicating that, under certain environmental and/or nutritional conditions, reduced photorespiratory capacity may be detrimental to plant performance. Here we summarize recent advances obtained in photorespiratory engineering and discuss prospects for these advances to be transferred to major crops to help address the globally increasing demand for food and biomass production.