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Stephen P Long - One of the best experts on this subject based on the ideXlab platform.
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bundle sheath chloroplast volume can house sufficient rubisco to avoid limiting c4 photosynthesis during chilling
Journal of Experimental Botany, 2019Co-Authors: Charles P Pignon, Colin P. Osborne, Marjorie R Lundgren, Stephen P LongAbstract:C4 leaves confine Rubisco to bundle sheath cells. Thus, the size of bundle sheath compartments and the total volume of chloroplasts within them limit the space available for Rubisco. Rubisco activity limits photosynthesis at low temperatures. C3 Plants counter this limitation by increasing leaf Rubisco content, yet few C4 species do the same. Because C3 Plants usually outperform C4 Plants in chilling environments, it has been suggested that there is insufficient chloroplast volume available in the bundle sheath of C4 leaves to allow such an increase in Rubisco at low temperatures. We investigated this potential limitation by measuring bundle sheath and mesophyll compartment volumes and chloroplast contents, as well as leaf thickness and inter-veinal distance, in three C4 Andropogoneae grasses: two crops (Zea mays and Saccharum officinarum) and a wild, chilling-tolerant grass (Miscanthus × giganteus). A wild C4 Paniceae grass (Alloteropsis semialata) was also included. Despite significant structural differences between species, there was no evidence of increased bundle sheath chloroplast volume per leaf area available to the chilling-tolerant species, relative to the chilling-sensitive ones. Maximal theoretical photosynthetic capacity of the leaf far exceeded the photosynthetic rates achieved even at low temperatures. C4 bundle sheath cells therefore have the chloroplast volume to house sufficient Rubisco to avoid limiting C4 photosynthesis during chilling.
Richard C. Leegood - One of the best experts on this subject based on the ideXlab platform.
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Roles of the bundle sheath cells in leaves of C3 Plants
Journal of experimental botany, 2008Co-Authors: Richard C. LeegoodAbstract:This review considers aspects of the structure and functions of the parenchymatous bundle sheath that surrounds the veins in the leaves of many C3 Plants. It includes a discussion of bundle sheath structure and its related structures (bundle sheath extensions and the paraveinal mesophyll), its relationship to the mestome sheath in some grasses, and its chloroplast content. Its metabolic roles in photosynthesis, carbohydrate synthesis and storage, the import and export of nitrogen and sulphur, and the metabolism of reactive oxygen species are discussed and are compared with the role of the bundle sheath in leaves of C4 Plants. Its role as an interface between the vasculature and the mesophyll is considered in relation to the movement of water and assimilates during leaf development, export of photosynthates, and senescence.
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C4 photosynthesis: principles of CO2 concentration and prospects for its introduction into C3 Plants
Journal of Experimental Botany, 2002Co-Authors: Richard C. LeegoodAbstract:C4 photosynthesis has a number of distinct properties that enable the capture of CO2 and its concentration in the vicinity of Rubisco, so as to reduce the oxygenase activity of Rubisco, and hence the rate of photorespiration. The aim of this review is to discuss the properties of this CO2-concentrating mechanism, and thus to indicate the minimum requirements of any genetically-engineered system. In particular, the Kranz leaf anatomy of C4 photosynthesis and the division of the C4-cycle between two cell types involves intercellular co-operation that requires modifications in regulation and transport to make C4 photosynthesis work. Some examples of these modifications are discussed. Comparisons are made with the C4-type photosynthesis found in single-celled C4-type CO2-concentrating mechanisms, such as that found in the aquatic plant, Hydrilla verticillata and the single-celled C4 system found in the terrestrial chenopod Borszczowia aralocaspica. The outcome of recent attempts to engineer C4 enzymes into C3 Plants is discussed.
Jaume Flexas - One of the best experts on this subject based on the ideXlab platform.
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mesophyll conductance to co2 and rubisco as targets for improving intrinsic water use efficiency in C3 Plants
Plant Cell and Environment, 2016Co-Authors: Jaume Flexas, Hipolito Medrano, Antonio Diazespejo, Miquel A Conesa, Rafael E Coopman, Cyril Douthe, Jorge Gago, Alexander Galle, Jeroni Galmes, Miquel RibascarboAbstract:Water limitation is a major global constraint for plant productivity that is likely to be exacerbated by climate change. Hence, improving plant water use efficiency (WUE) has become a major goal for the near future. At the leaf level, WUE is the ratio between photosynthesis and transpiration. Maintaining high photosynthesis under water stress, while improving WUE requires either increasing mesophyll conductance (gm ) and/or improving the biochemical capacity for CO2 assimilation-in which Rubisco properties play a key role, especially in C3 Plants at current atmospheric CO2 . The goals of the present analysis are: (1) to summarize the evidence that improving gm and/or Rubisco can result in increased WUE; (2) to review the degree of success of early attempts to genetically manipulate gm or Rubisco; (3) to analyse how gm , gsw and the Rubisco's maximum velocity (Vcmax ) co-vary across different plant species in well-watered and drought-stressed conditions; (4) to examine how these variations cause differences in WUE and what is the overall extent of variation in individual determinants of WUE; and finally, (5) to use simulation analysis to provide a theoretical framework for the possible control of WUE by gm and Rubisco catalytic constants vis-a-vis gsw under water limitations.
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diffusive and metabolic limitations to photosynthesis under drought and salinity in C3 Plants
Plant Biology, 2004Co-Authors: Jaume Flexas, Josefina Bota, Francesco Loreto, G Cornic, Thomas D. SharkeyAbstract:Drought and salinity are two widespread environmental conditions leading to low water availability for Plants. Low water availability is considered the main environmental factor limiting photosynthesis and, consequently, plant growth and yield worldwide. There has been a long-standing controversy as to whether drought and salt stresses mainly limit photosynthesis through diffusive resistances or by metabolic impairment. Reviewing in vitro and in vivo measurements, it is concluded that salt and drought stress predominantly affect diffusion of CO(2) in the leaves through a decrease of stomatal and mesophyll conductances, but not the biochemical capacity to assimilate CO(2), at mild to rather severe stress levels. The general failure of metabolism observed at more severe stress suggests the occurrence of secondary oxidative stresses, particularly under high-light conditions. Estimates of photosynthetic limitations based on the photosynthetic response to intercellular CO(2) may lead to artefactual conclusions, even if patchy stomatal closure and the relative increase of cuticular conductance are taken into account, as decreasing mesophyll conductance can cause the CO(2) concentration in chloroplasts of stressed leaves to be considerably lower than the intercellular CO(2) concentration. Measurements based on the photosynthetic response to chloroplast CO(2) often confirm that the photosynthetic capacity is preserved but photosynthesis is limited by diffusive resistances in drought and salt-stressed leaves.
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regulation of photosynthesis of C3 Plants in response to progressive drought stomatal conductance as a reference parameter
Annals of Botany, 2002Co-Authors: Hipolito Medrano, Jose Mariano Escalona, Josefina Bota, Javier Gulias, Jaume FlexasAbstract:We review the photosynthetic responses to drought in field-grown grapevines and other species. As in other plant species, the relationship between photosynthesis and leaf water potential and/or relative water content in field-grown grapevines depends on conditions during plant growth and measurements. However, when light-saturated stomatal conductance was used as the reference parameter to reflect drought intensity, a common response pattern was observed that was much less dependent on the species and conditions. Many photosynthetic parameters (e.g. electron transport rate, carboxylation efficiency, intrinsic water-use efficiency, respiration rate in the light, etc.) were also more strongly correlated with stomatal conductance than with water status itself. Moreover, steady-state chlorophyll fluorescence also showed a high dependency on stomatal conductance. This is discussed in terms of an integrated down-regulation of the whole photosynthetic process by CO2 availability in the mesophyll. A study with six Mediterranean shrubs revealed that, in spite of some marked interspecific differences, all followed the same pattern of dependence of photosynthetic processes on stomatal conductance, and this pattern was quite similar to that of grapevines. Further analysis of the available literature suggests that the above-mentioned pattern is general for C3 Plants. Even though the patterns described do not necessarily imply a cause and effect relationship, they can help our understanding of the apparent contradictions concerning stomatal vs. non-stomatal limitations to photosynthesis under drought. The significance of these findings for the improvement of water-use efficiency of crops is discussed. a 2002 Annals of Botany Company
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drought inhibition of photosynthesis in C3 Plants stomatal and non stomatal limitations revisited
Annals of Botany, 2002Co-Authors: Jaume Flexas, Hipolito MedranoAbstract:There is a long-standing controversy as to whether drought limits photosynthetic CO2 assimilation through stomatal closure or by metabolic impairment in C3 Plants. Comparing results from different studies is difficult due to interspecific differences in the response of photosynthesis to leaf water potential and/or relative water content (RWC), the most commonly used parameters to assess the severity of drought. Therefore, we have used stomatal conductance (g) as a basis for comparison of metabolic processes in different studies. The logic is that, as there is a strong link between g and photosynthesis (perhaps co-regulation between them), so different relationships between RWC or water potential and photosynthetic rate and changes in metabolism in different species and studies may be 'normalized' by relating them to g. Re-analysing data from the literature using light-saturated g as a parameter indicative of water deficits in Plants shows that there is good correspondence between the onset of drought-induced inhibition of different photosynthetic sub-processes and g. Contents of ribulose bisphosphate (RuBP) and adenosine triphosphate (ATP) decrease early in drought development, at still relatively high g (higher than 150 mmol H20 m(-2) s(-1)). This suggests that RuBP regeneration and ATP synthesis are impaired. Decreased photochemistry and Rubisco activity typically occur at lower g (<100 mmol H20 m(-2) s(-1)), whereas permanent photoinhibition is only occasional, occurring at very low g (<50 mmol H20 m(-2) s(-1)). Sub-stomatal CO2 concentration decreases as g becomes smaller, but increases again at small g. The analysis suggests that stomatal closure is the earliest response to drought and the dominant limitation to photosynthesis at mild to moderate drought. However, in parallel, progressive down-regulation or inhibition of metabolic processes leads to decreased RuBP content, which becomes the dominant limitation at severe drought, and thereby inhibits photosynthetic CO2 assimilation.
Christoph Peterhänsel - One of the best experts on this subject based on the ideXlab platform.
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Best practice procedures for the establishment of a C4 cycle in transgenic C3 Plants
Journal of experimental botany, 2011Co-Authors: Christoph PeterhänselAbstract:C4 Plants established a mechanism for the concentration of CO2 in the vicinity of ribulose-1,5-bisphosphate carboxylase/oxygenase in order to saturate the enzyme with substrate and substantially to reduce the alternative fixation of O2 that results in energy losses. Transfer of the C4 mechanism to C3 Plants has been repeatedly tested, but none of the approaches so far resulted in transgenic Plants with enhanced photosynthesis or growth. Instead, often deleterious effects were observed. A true C4 cycle requires the co-ordinated activity of multiple enzymes in different cell types and in response to diverse environmental and metabolic stimuli. This review summarizes our current knowledge about the most appropriate regulatory elements and coding sequences for the establishment of C4 protein activities in C3 Plants. In addition, technological breakthroughs for the efficient transfer of the numerous genes probably required to transform a C3 plant into a C4 plant will be discussed.
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an engineered phosphoenolpyruvate carboxylase redirects carbon and nitrogen flow in transgenic potato Plants
Plant Journal, 2002Co-Authors: Thomas W Rademacher, Rainer E. Häusler, Heinz-josef Hirsch, Fritz Kreuzaler, Li Zhang, Volker Lipka, Dagmar Weier, Christoph PeterhänselAbstract:Phosphoenolpyruvate carboxylase (PEPC) plays a central role in the anaplerotic provision of carbon skeletons for amino acid biosynthesis in leaves of C3 Plants. Furthermore, in both C4 and CAM Plants photosynthetic isoforms are pivotal for the fixation of atmospheric CO2. Potato PEPC was mutated either by modifications of the N-terminal phosphorylation site or by an exchange of an internal cDNA segment for the homologous sequence of PEPC from the C4 plant Flaveria trinervia. Both modifications resulted in enzymes with lowered sensitivity to malate inhibition and an increased affinity for PEP. These effects were enhanced by a combination of both mutated sequences and pulse labelling with 14CO2 in vivo revealed clearly increased fixation into malate for this genotype. Activity levels correlated well with protein levels of the mutated PEPC. Constitutive overexpression of PEPC carrying both N-terminal and internal modifications strongly diminished plant growth and tuber yield. Metabolite analysis showed that carbon flow was re-directed from soluble sugars and starch to organic acids (malate) and amino acids, which increased four-fold compared with the wild type. The effects on leaf metabolism indicate that the engineered enzyme provides an optimised starting point for the installation of a C4-like photosynthetic pathway in C3 Plants.
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Overexpression of C4-cycle enzymes in transgenic C3 Plants: a biotechnological approach to improve C3-photosynthesis
Journal of experimental botany, 2002Co-Authors: Rainer E. Häusler, Heinz-josef Hirsch, Fritz Kreuzaler, Christoph PeterhänselAbstract:The process of photorespiration diminishes the efficiency of CO2 assimilation and yield of C3-crops such as wheat, rice, soybean or potato, which are important for feeding the growing world population. Photorespiration starts with the competitive inhibition of CO2 fixation by O2 at the active site of ribulose1,5-bisphosphate carboxylase/oxygenase (Rubisco) and can result in a loss of up to 50% of the CO2 fixed in ambient air. By contrast, C4 Plants, such as maize, sugar cane and Sorghum, possess a CO2 concentrating mechanism, by which atmospheric CO2 is bound to C4-carbon compounds and shuttled from the mesophyll cells where the prefixation of bicarbonate occurs via phosphoenolpyruvate carboxylase (PEPC) into the gas-tight bundle-sheath cells, where the bound carbon is released again as CO2 and enters the Calvin cycle. However, the anatomical division into mesophyll and bundle-sheaths cells (‘Kranz’anatomy) appears not to be a prerequisite for the operation of a CO2 concentrating mechanism. Submergedaquaticmacrophytes,forinstance,caninduce aC 4-like CO2 concentrating mechanism in only one cell type when CO2 becomes limiting. A single cell C4-mechanism has also been reported recently for a terrestrial chenopod. For over 10 years researchers in laboratories around the world have attempted to improve photosynthesis and crop yield by introducing a single cell C4-cycle in C3 Plants by a transgenic approach. In the meantime, there has been substantial progress in overexpressing the key enzymes of the C4 cycle in rice, potato, and tobacco. In this review there will be a focus on biochemical and physiological consequences of the overexpression of C4-cycle genes in C3 Plants. Bearing in mind that C4-cycle enzymes are also present in C3 Plants, the pitfalls encountered when C3 metabolism is perturbed by the overexpression of individual C4 genes will also be discussed.
Marjorie R Lundgren - One of the best experts on this subject based on the ideXlab platform.
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bundle sheath chloroplast volume can house sufficient rubisco to avoid limiting c4 photosynthesis during chilling
Journal of Experimental Botany, 2019Co-Authors: Charles P Pignon, Colin P. Osborne, Marjorie R Lundgren, Stephen P LongAbstract:C4 leaves confine Rubisco to bundle sheath cells. Thus, the size of bundle sheath compartments and the total volume of chloroplasts within them limit the space available for Rubisco. Rubisco activity limits photosynthesis at low temperatures. C3 Plants counter this limitation by increasing leaf Rubisco content, yet few C4 species do the same. Because C3 Plants usually outperform C4 Plants in chilling environments, it has been suggested that there is insufficient chloroplast volume available in the bundle sheath of C4 leaves to allow such an increase in Rubisco at low temperatures. We investigated this potential limitation by measuring bundle sheath and mesophyll compartment volumes and chloroplast contents, as well as leaf thickness and inter-veinal distance, in three C4 Andropogoneae grasses: two crops (Zea mays and Saccharum officinarum) and a wild, chilling-tolerant grass (Miscanthus × giganteus). A wild C4 Paniceae grass (Alloteropsis semialata) was also included. Despite significant structural differences between species, there was no evidence of increased bundle sheath chloroplast volume per leaf area available to the chilling-tolerant species, relative to the chilling-sensitive ones. Maximal theoretical photosynthetic capacity of the leaf far exceeded the photosynthetic rates achieved even at low temperatures. C4 bundle sheath cells therefore have the chloroplast volume to house sufficient Rubisco to avoid limiting C4 photosynthesis during chilling.
