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1.
C4 photosynthesis in C3 rice: a theoretical analysis of biochemical and anatomical factors
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Engineering C4 photosynthesis into rice has been considered a promising strategy to increase photosynthesis and yield. A question that remains to be answered is whether expressing a C4 metabolic cycle into a C3 leaf structure and without removing the C3 background metabolism improves photosynthetic efficiency. To explore this question, we developed a 3D reaction diffusion model of bundle‐sheath and connected mesophyll cells in a C3 rice leaf. Our results show that integrating a C4 metabolic pathway into rice leaves with a C3 metabolism and mesophyll structure may lead to an improved photosynthesis under current ambient CO2 concentration. We analysed a number of physiological factors that influence the CO2 uptake rate, which include the chloroplast surface area exposed to intercellular air space, bundle‐sheath cell wall thickness, bundle‐sheath chloroplast envelope permeability, Rubisco concentration and the energy partitioning between C3 and C4 cycles. Among these, partitioning of energy between C3 and C4 photosynthesis and the partitioning of Rubisco between mesophyll and bundle‐sheath cells are decisive factors controlling photosynthetic efficiency in an engineered C3–C4 leaf. The implications of the results for the sequence of C4 evolution are also discussed. 相似文献
2.
The C4 pathway: an efficient CO2 pump 总被引:2,自引:0,他引:2
The C4 pathway is a complex combination of both biochemical and morphological specialisation, which provides an elevation of the
CO2 concentration at the site of Rubisco. We review the key parameters necessary to make the C4 pathway function efficiently, focussing on the diffusion of CO2 out of the bundle sheath compartment. Measurements of cell wall thickness show that the thickness of bundle sheath cell walls
in C4 species is similar to cell wall thickness of C3 mesophyll cells. Furthermore, NAD-ME type C4 species, which do not have suberin in their bundle sheath cell walls, do not appear to compensate for this with thicker bundle
sheath cell walls. Uncertainties in the CO2 diffusion properties of membranes, such as the plasmalemma, choroplast and mitochondrial membranes make it difficult to estimate
bundle sheath diffusion resistance from anatomical measurements, but the cytosol itself may account for more than half of
the final calculated resistance value for CO2 leakage. We conclude that the location of the site of decarboxylation, its distance from the mesophyll interface and the
physical arrangement of chloroplasts and mitochondria in the bundle sheath cell are as important to the efficiency of the
process as the properties of the bundle sheath cell wall. Using a mathemathical model of C4 photosynthesis, we also examine the relationship between bundle sheath resistance to CO2 diffusion and the biochemical capacity of the C4 photosynthetic pathway and conclude that bundle sheath resistance to CO2 diffusion must vary with biochemical capacity if the efficiency of the C4 pump is to be maintained. Finally, we construct a mathematical model of single cell C4 photosynthesis in a C3 mesophyll cell and examine the theoretical efficiency of such a C4 photosynthetic CO2 pump.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Low bundle sheath carbonic anhydrase is apparently essential for effective c(4) pathway operation 总被引:11,自引:8,他引:3
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Bundle sheath cells from leaves of a variety of C4 species contained little or no carbonic anhydrase activity. The proportion of total leaf carbonic anhydrase in extracts of bundle sheath cells closely reflected the apparent mesophyll cell contamination of bundle sheath cell extracts as measured by the proportion of the mesophyll cell marker enzymes phosphoenolpyruvate carboxylase and pyruvate,Pi dikinase. Values of about 1% or less of the total leaf activity were obtained for all three enzymes. The recorded bundle sheath carbonic anhydrase activity was compared with a calculated upper limit of carbonic anhydrase activity that would still permit efficient functioning of the C4 pathway; that is, a carbonic anhydrase level allowing a sufficiently high steady state [CO2] to suppress photorespiration. Even before correcting for mesophyll cell contamination the activity in bundle sheath cell extracts was substantially less than the calculated upper limit of carbonic anhydrase activity consistent with effective C4 function. The results accord with the notion that a deficiency of carbonic anhydrase in bundle sheath cells is vital for the efficient operation of the C4 pathway. 相似文献
4.
5.
Carbon Sink-to-Source Transition Is Coordinated with Establishment of Cell-Specific Gene Expression in a C4 Plant 总被引:8,自引:1,他引:7
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Plants that use the highly efficient C4 photosynthetic pathway possess two types of specialized leaf cells, the mesophyll and bundle sheath. In mature C4 leaves, the CO2 fixation enzyme ribulose-1,5-bisphosphate carboxylase (RuBPCase) is specifically compartmentalized to the bundle sheath cells. However, in very young leaves of amaranth, a dicotyledonous C4 plant, genes encoding the large subunit and small subunit of RuBPCase are initially expressed in both photosynthetic cell types. We show here that the RuBPCase mRNAs and proteins become specifically localized to leaf bundle sheath cells during the developmental transition of the leaf from carbon sink to carbon source. Bundle sheath cell-specific expression of RuBPCase genes and the sink-to-source transition began initially at the leaf apex and progressed rapidly and coordinately toward the leaf base. These findings demonstrated that two developmental transitions, the change in photoassimilate transport status and the establishment of bundle sheath cell-specific RuBPCase gene expression, are tightly coordinated during C4 leaf development. This correlation suggests that processes associated with the accumulation and transport of photosynthetic compounds may influence patterns of photosynthetic gene expression in C4 plants. 相似文献
6.
Effects of Polyploidy on Photosynthetic Rates, Photosynthetic Enzymes, Contents of DNA, Chlorophyll, and Sizes and Numbers of Photosynthetic Cells in the C(4) Dicot Atriplex confertifolia
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Photosynthetic rates, chlorophyll content, and activities of several photosynthetic enzymes were determined per cell, per unit DNA, and per unit leaf area in five ploidal levels of the C4 dicot Atriplex confertifolia. Volumes of bundle sheath and mesophyll protoplasts were measured in enzymatic digestions of leaf tissue. Photosynthetic rates per cell, contents of DNA per cell, and activities of the bundle sheath enzymes ribulose 1,5-bisphosphate carboxylase (RuBPC) and NAD-malic enzyme per cell were correlated with ploidal level at 99% or 95% confidence levels, and the results suggested a near proportional relationship between gene dosage and gene products. There was also a high correlation between volume of mesophyll and bundle sheath cells and the ploidal level. Contents of DNA per cell, activity of RuBPC per cell, and volumes of cells were correlated with photosynthetic rate per cell at the 95% confidence level. The mesophyll cells did not respond to changes in ploidy like the bundle sheath cells. In the mesophyll cells the chlorophyll content per cell was constant at different ploidal levels, there was less increase in cell volume than in bundle sheath cells with an increase in ploidy, and there was not a significant correlation (at 95% level) of phosphoenolpyruvate carboxylase activity or content and pyruvate,Pi dikinase activity with increase in ploidy. The number of photosynthetic cells per unit leaf area progressively decreased with increasing ploidy from diploid to hexaploid, but thereafter remained constant in octaploid and decaploid plants. Numbers of cells per leaf area were not correlated with cell volumes. The mean photosynthetic rates per unit leaf area were lowest in the diploid, similar in 4×, 6×, and 8×, and highest in the decaploid. The photosynthetic rate per leaf area was highly correlated with the DNA content per leaf area. 相似文献
7.
Nancy G. Dengler Ronald E. Dengler Petra M. Donnelly Michael F. Filosa 《American journal of botany》1995,82(3):318-327
Immunolocalization of the bundle sheath-specific enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCase), and of the mesophyll-specific enzyme, phosphoenolpyruvate carboxylase (PEPCase), was used to follow development of the C4 pattern of photosynthetic enzyme expression during leaf growth in Atriplex rosea. The leaf tissue used for this characterization was also used in a parallel ultrastructural study, so that the temporal coordination of developmental changes in enzyme expression and cell structure could be monitored. Bundle sheath-specific accumulation of RuBPCase occurs early, at the time that bundle sheath tissue is delimited from the ground meristem, and follows the order of vein initiation. PEPCase proteins were detected 2–4 days after the first appearance of RuBPCase. PEPCase accumulation is restricted to ground meristem cells that are in direct contact with bundle sheath tissue and that will become C4 mesophyll; PEPCase was never found in more distant ground tissue. This pattern suggests that, while bundle sheath-specific accumulation of RuBPCase coincides with formation of the appropriate precursor cells, PEPCase expression is delayed until mesophyll tissue reaches a critical developmental stage. Cell-specific expression of both photosynthetic enzymes occurs well before the striking anatomical divergence of bundle sheath and mesophyll tissues, suggesting that biochemical compartmentation might serve as a developmental signal for subsequent structural differentiation. 相似文献
8.
Photosynthesis in Flaveria brownii, a C(4)-Like Species: Leaf Anatomy, Characteristics of CO(2) Exchange, Compartmentation of Photosynthetic Enzymes, and Metabolism of CO(2)
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Light microscopic examination of leaf cross-sections showed that Flaveria brownii A. M. Powell exhibits Kranz anatomy, in which distinct, chloroplast-containing bundle sheath cells are surrounded by two types of mesophyll cells. Smaller mesophyll cells containing many chloroplasts are arranged around the bundle sheath cells. Larger, spongy mesophyll cells, having fewer chloroplasts, are located between the smaller mesophyll cells and the epidermis. F. brownii has very low CO2 compensation points at different O2 levels, which is typical of C4 plants, yet it does show about 4% inhibition of net photosynthesis by 21% O2 at 30°C. Protoplasts of the three photosynthetic leaf cell types were isolated according to relative differences in their buoyant densities. On a chlorophyll basis, the activities of phosphoenolpyruvate carboxylase and pyruvate, Pi dikinase (carboxylation phase of C4 pathway) were highest in the larger mesophyll protoplasts, intermediate in the smaller mesophyll protoplasts, and lowest, but still present, in the bundle sheath protoplasts. In contrast, activities of ribulose 1,5-bisphosphate carboxylase, other C3 cycle enzymes, and NADP-malic enzyme showed a reverse gradation, although there were significant activities of these enzymes in mesophyll cells. As indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the banding pattern of certain polypeptides of the total soluble proteins from the three cell types also supported the distribution pattern obtained by activity assays of these enzymes. Analysis of initial 14C products in whole leaves and extrapolation of pulse-labeling curves to zero time indicated that about 80% of the CO2 is fixed into C4 acids (malate and aspartate), whereas about 20% of the CO2 directly enters the C3 cycle. This is consistent with the high activity of enzymes for CO2 fixation by the C4 pathway and the substantial activity of enzymes of the C3 cycle in the mesophyll cells. Therefore, F. brownii appears to have some capacity for C3 photosynthesis in the mesophyll cells and should be considered a C4-like species. 相似文献
9.
Metabolism of epidermal tissues, mesophyll cells, and bundle sheath strands resolved from mature nutsedge leaves 总被引:6,自引:0,他引:6
T M Chen P Dittrich W H Campbell C C Black 《Archives of biochemistry and biophysics》1974,163(1):246-262
Mesophyll cells and bundle sheath strands were isolated from Cyperus rotundus L. leaf sections infiltrated with a mixture of cellulase and pectinase followed by a gentle mortar and pestle grind. The leaf suspension was filtered through a filter assembly and mesophyll cells and bundle sheath strands were collected on 20-μm and 80-μm nylon nets, respectively. For the isolation of leaf epidermal strips longer leaf cross sections were incubated with the enzymes and gently ground as above. Loosely attached epidermal strips were peeled off with forceps. The upper epidermis, which lacks stomata, could be clearly distinguished from the lower epidermis which contains stomata. Microscopic evidence for identification and assessment of purity is provided for each isolated tissue.Enzymes related to the C4-dicarboxylic acid cycle such as phosphoenolpyruvate carboxylase, malate dehydrogenase (NADP+), pyruvate, Pi dikinase were found to be localized, ≥98%, in mesophyll cells. Enzymes related to operating the reductive pentose phosphate cycle such as RuDP carboxylase, phosphoribulose kinase, and malic enzyme are distributed, ≥99%, in bundle sheath strands. Other photosynthetic enzymes such as aspartate aminotransferase, pyrophosphatase, adenylate kinase, and glyceraldehyde 3-P dehydrogenase (NADP+) are quite active in both mesophyll and bundle sheath tissues.Enzymes involved in photorespiration such as RuDP oxygenase, catalase, glycolate oxidase, hydroxypyruvate reductase (NAD+), and phosphoglycolate phosphatase are preferentially localized, ≥84%, in bundle sheath strands.Nitrate and nitrite reductase can be found only in mesophyll cells, while glutamate dehydrogenase is present, ≥96%, in bundle sheath strands.Starch- and sucrose-synthesizing enzymes are about equally distributed between the mesophyll and bundle sheath tissues, except that the less active phosphorylase was found mainly in bundle sheath strands. Fructose-1,6-diP aldolase, which is a key enzyme in photosynthesis and glycolysis leading to sucrose and starch synthesis, is localized, ≥90%, in bundle sheath strands. The glycolytic enzymes, phosphoglyceromutase and enolase, have the highest activity in mesophyll cells, while the mitochondrial enzyme, cytochrome c oxidase, is more active in bundle sheath strands.The distribution of total nutsedge leaf chlorophyll, protein, and PEP carboxylase activity, using the resolved leaf components, is presented. 14CO2 Fixation experiments with the intact nutsedge leaves and isolated mesophyll and bundle sheath tissues show that complete C4 photosynthesis is compartmentalized into mesophyll CO2 fixation via PEP carboxylase and bundle sheath CO2 fixation via RuDP carboxylase. These results were used to support the proposed pathway of carbon assimilation in C4-dicarboxylic acid photosynthesis and to discuss the individual metabolic characteristics of intact mesophyll cells, bundle sheath cells, and epidermal tissues. 相似文献
10.
11.
Photosynthetic Characteristics of Portulaca grandiflora, a Succulent C(4) Dicot : CELLULAR COMPARTMENTATION OF ENZYMES AND ACID METABOLISM 总被引:4,自引:4,他引:0
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The succulent, cylindrical leaves of the C4 dicot Portulaca grandiflora possess three distinct green cell types: bundle sheath cells (BSC) in radial arrangement around the vascular bundles; mesophyll cells (MC) in an outer layer adjacent to the BSC; and water storage cells (WSC) in the leaf center. Unlike typical Kranz leaf anatomy, the MC do not surround the bundle sheath tissue but occur only in the area between the bundle sheath and the epidermis. Intercellular localization of photosynthetic enzymes was characterized using protoplasts isolated enzymatically from all three green cell types. 相似文献
12.
Marjorie R. Lundgren Andrew J. Fleming 《The Plant journal : for cell and molecular biology》2020,101(4):845-857
After entering the leaf, CO2 faces an intricate pathway to the site of photosynthetic fixation embedded within the chloroplasts. The efficiency of CO2 flux is hindered by a number of structural and biochemical barriers which, together, define the ease of flow of the gas within the leaf, termed mesophyll conductance. Previous authors have identified the key elements of this pathway, raising the prospect of engineering the system to improve CO2 flux and, thus, to increase leaf photosynthetic efficiency. In this review, we provide a perspective on the potential for improving the individual elements that contribute to this complex parameter. We lay particular emphasis on generation of the cellular architecture of the leaf which sets the initial boundaries of a number of mesophyll conductance parameters, incorporating an overview of the molecular transport processes which have been proposed as major facilitators of CO2 flux across structural boundaries along the pathway. The review highlights the research areas where future effort might be invested to increase our fundamental understanding of mesophyll conductance and leaf function and, consequently, to enable translation of these findings to improve the efficiency of crop photosynthesis. 相似文献
13.
Metabolic Activities in Extracts of Mesophyll and Bundle Sheath Cells of Panicum miliaceum (L.) in Relation to the C(4) Dicarboxylic Acid Pathway of Photosynthesis 总被引:7,自引:7,他引:0
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The activities of certain enzymes related to the carbon assimilation pathway in whole leaves, mesophyll cell extracts, and bundle sheath extracts of the C4 plant Panicum miliaceum have been measured and compared on a chlorophyll basis. Enzymes of the C4 dicarboxylic acid pathway—phosphoenolpyruvate carboxylase and NADP-malic dehydrogenase—were localized in mesophyll cells. Carbonic anhydrase was also localized in mesophyll cell extracts. Ribose 5-phosphate isomerase, ribulose 5-phosphate kinase, and ribulose diphosphate carboxylase—enzymes of the reductive pentose phosphate pathway—were predominantly localized in bundle sheath extracts. High activities of aspartate and alanine transaminases and glyceraldehyde-3-P dehydrogenase were found about equally distributed between the photosynthetic cell types. P. miliaceum had low malic enzyme activity in both mesophyll and bundle sheath extracts. 相似文献
14.
Distribution of Photosynthetic Enzymes between Mesophyll, Specialized Parenchyma and Bundle Sheath Cells of Arundinella hirta
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Arundinella hirta L. is a C4 plant having an unusual C4 leaf anatomy. Besides mesophyll and bundle sheath cells, A. hirta leaves have specialized parenchyma cells which look morphologically like bundle sheath cells but which lack vascular connections and are located between veins, running parallel to them. Activities of phosphoenolpyruvate and ribulose-1,5-bisphosphate carboxylases and phosphoenolpyruvate carboxykinase, NADP-and NAD-malic enzymes were determined for whole leaf extracts and isolated mesophyll protoplasts, specialized parenchyma cells, and bundle sheath cells. The data indicate that A. hirta is a NADP-malic enzyme type C4 species. In addition, specialized parenchyma cells and bundle sheath cells are enzymatically alike. Compartmentation of enzymes followed the C4 pattern with phosphoenolpyruvate carboxylase being restricted to mesophyll cells while ribulose-1,5-bisphosphate carboxylase and decarboxylating enzymes were restricted to bundle sheath and specialized parenchyma cells. 相似文献
15.
Two-Dimensional Electrophoretic Mapping of Proteins of Bundle Sheath and Mesophyll Cells of the C(4) Grass Digitaria sanguinalis (L.) Scop. (Crabgrass) 总被引:3,自引:3,他引:0
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Two-dimensional electrophoresis was performed on proteins of bundle sheath and mesophyll cells isolated from the C4 grass Digitaria sanguinalis (L.) Scop. Two-dimensional maps of these proteins were constructed and ribulose-1,5-biphosphate carboxylase and phosphoenolpyruvate carboxylase were identified. Of the total number of proteins found in both cell types, 36% were found only in bundle sheath cells, 17% only in mesophyll cells, and 47% in both cell types. By comparison, the distributions of 48 enzymes assayed in these cell types were 35%, 21%, and 44%, respectively.
Protein patterns were also compared with C4 plants exhibiting different decarboxylation pathways and, in both bundle sheath and mesophyll cells, proteins were found which were unique to each species. Bundle sheath proteins of one C4 species were found to be more like bundle sheath proteins of another C4 species than like mesophyll proteins of the same species.
相似文献16.
Mesophyll protoplasts and bundle sheath cells were prepared by enzymatic digestion of leaves of Alternanthera tenella, a C3-C4 intermediate species. The intercellular distribution of selected photosynthetic, photorespiratory and respiratory (mitochondrial) enzymes in these meso-phyll and bundle sheath cells was studied. The activity levels of photosynthetic enzymes such as PEP carboxylase (EC 4.1.1.31) or NAD-malic enzyme (EC 1.1.1.39) and photorespiratory enzymes such as glycolate oxidase (EC 1.1.3.1) or NADH-hydroxypyruvate reductase (EC 1.1.1.29) were similar in the two cell types. The activity levels of mitochondrial TCA cycle enzymes such as citrate synthase (EC 4.1.3.7) or fumarase (EC 4.2.1.2) were 2- to 3-fold higher in bundle sheath cells. On the other hand, the activity levels of mitochondrial photorespiratory enzymes, namely glycine decarboxylase (EC 2.1.2.10) and serine hydroxymethyltransferase (EC 2.1.2.1), were 6-9-fold higher in bundle sheath cells than in mesophyll protoplasts. Such preferential localization of mitochondria enriched with the glycine-decarboxylating system in the inner bundle sheath cells would result in efficient refixa-tion of CO2 from not only photorespiration but also dark respiration before its exit from the leaf. We propose that predominant localization of mitochondria specialized in glycine decarboxylation in bundle sheath cells may form the basis of reduced photorespiration in this C3-C4 intermediate species. 相似文献
17.
Potassium mediates coordination of leaf photosynthesis and hydraulic conductance by modifications of leaf anatomy 总被引:1,自引:0,他引:1
Zhifeng Lu Kailiu Xie Yonghui Pan Tao Ren Jianwei Lu Min Wang Qirong Shen Shiwei Guo 《Plant, cell & environment》2019,42(7):2231-2244
Typical symptoms of potassium deficiency, characterized as chlorosis or withered necrosis, occur concomitantly with downregulated photosynthesis and impaired leaf water transport. However, the prominent limitations and mechanisms underlying the concerted decreases of leaf photosynthesis and hydraulic conductance are poorly understood. Monocots and dicots were investigated based on responses of photosynthesis and hydraulic conductance and their components and the correlated anatomical determinants to potassium deficiency. We found a conserved pattern in which leaf photosynthesis and hydraulic conductance concurrently decreased under potassium starvation. However, monocots and dicots showed two different hydraulic‐redesign strategies: Dicots tended to show a decreased minor vein density, whereas monocots reduced the size of the bundle sheath and its extensions, rather than the minor vein density; both of these strategies may restrain xylem and outside‐xylem hydraulic conductance. Additionally, potassium‐deprived leaves developed with fewer mesophyll cell‐to‐cell connections, leading to a reduced area being available for liquid‐phase flow. Further quantitative analysis revealed that mesophyll conductance to CO2 and outside‐xylem hydraulic resistance were the major contributors to photosynthetic limitation and increased hydraulic resistance, at more than 50% and 60%, respectively. These results emphasize the importance of potassium in the coordinated regulation of leaf photosynthesis and hydraulic conductance through modifications of leaf anatomy. 相似文献
18.
Photosynthetic Enzyme Activities and Localization in Mollugo verticillata Populations Differing in the Levels of C(3) and C(4) Cycle Operation 总被引:3,自引:1,他引:2
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Ecotypic differences in the photosynthetic carbon metabolism of Mollugo verticillata were studied. Variations in C3 and C4 cycle activity are apparently due to differences in the activities of enzymes associated with each pathway. Compared to C4 plants, the activities of C4 pathway enzymes were generally lower in M. verticillata, with the exception of the decarboxylase enzyme, NAD malic enzyme. The combined total carboxylase enzyme activity of M. verticillata was greater than that of C3 plants, possibly accounting for the high photosynthetic rates of this species. Unlike either C3 or C4 plants, ribulose bisphosphate carboxylase was present in both mesophyll and bundle sheath cell chloroplasts in M. verticillata. The localization of this enzyme in both cells in this plant, in conjunction with an efficient C4 acid decarboxylation mechanism most likely localized in bundle sheath cell mitochondria, may account for intermediate photorespiration levels previously observed in this species. 相似文献
19.