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1.
Chloroplast photorelocation movement is extensively studied in C 3 but not C 4 plants. C 4 plants have two types of photosynthetic cells: mesophyll and bundle sheath cells. Mesophyll chloroplasts are randomly distributed along cell walls, whereas bundle sheath chloroplasts are located close to the vascular tissues or mesophyll cells depending on the plant species. The cell-specific C 4 chloroplast arrangement is established during cell maturation, and is maintained throughout the life of the cell. However, only mesophyll chloroplasts can change their positions in response to environmental stresses. The migration pattern is unique to C 4 plants and differs from that of C 3 chloroplasts. in this mini-review, we highlight the cell-specific disposition of chloroplasts in C 4 plants and discuss the possible physiological significances.Key words: abscisic acid, aggregative movement, avoidance movement, blue light, bundle sheath cell, C4 plant, chloroplast, cytoskeleton, environmental stress, mesophyll cellChloroplasts can change their intracellular positions to optimize photosynthetic activity and/or reduce photodamage occurring in response to light irradiation. On treating with high-intensity light, the chloroplasts move away from the light to minimize photodamage (avoidance response). Meanwhile, on irradiating with low-intensity light, they move toward the light source to maximize photosynthesis (accumulation response). These chloroplast-photorelocation movements are observed in a wide variety of plant species from green algae to seed plants, 1–3 although little attention has been paid to C 4 plants. There is a report stating that monocotyledonous C 4 plants showed changes in the light transmission of leaves in response to blue light, 4 although the direction of migration of the chloroplasts is not described.C 4 plants have two types of photosynthetic cells: mesophyll (M) cells and bundle sheath (BS) cells, which have numerous well-developed chloroplasts. BS cells surround the vascular tissues, while M cells encircle the cylinders of the BS cells (). The C 4 dicarboxylate cycle of photosynthetic carbon assimilation is distributed between the two cell types, and acts as a CO 2 pump to concentrate CO 2 in the BS chloroplasts. 5,6 C 4 plants are divided into three subtypes on the basis of decarboxylating enzymes: NADP-malic enzyme (ME), NAD-ME and phospho enolpyruvate carboxykinase. Although the M chloroplasts of all C 4 species are randomly distributed along the cell walls, BS chloroplasts are located either in a centripetal (close to the vascular tissue) or in a centrifugal (close to M cells) position, depending on the species (). 7 Thus, C 4 M and BS cells have different systems for chloroplast positioning: an M cell-specific system for dispersing chloroplasts and a BS cell-specific system for holding chloroplasts in a centripetal or centrifugal disposition. Open in a separate windowThe intracellular arrangement of chloroplasts in finger millet ( Eleusine coracana), an NAD-ME-type C 4 plant. (A) Light micrograph of a transverse section of a leaf blade from a control plant. Bundle sheath (BS) cells surround the vascular tissues, while mesophyll (M) cells encircle the cylinders of the BS cells. BS chloroplasts are well developed, and are located in a centripetal position, whereas M chloroplasts are randomly distributed along the cell walls. B, bundle sheath cell; M, mesophyll cell; V, vascular bundle. (B) Transverse section of a leaf blade from a drought-stressed plant. Most M chloroplasts are aggregatively distributed toward the BS side, while the centripetal arrangement of BS chloroplasts is unchanged. (C and D) Transverse sections of leaf segments irradiated with blue light of intensity 500 µmol m −2 s −1 with or without 30 µM ABA for 8 h (C and D, respectively). The adaxial side of each leaf section (upper side in the photograph) was illuminated. In the absence of ABA, M chloroplasts exhibited avoidance movement on the illuminated side and aggregative movement on the opposite side. In the presence of ABA, aggregative movement was observed on both sides. Scale bars = 50 µm. 相似文献
2.
Rapid metabolite diffusion across the mesophyll (M) and bundle sheath (BS) cell interface in C 4 leaves is a key requirement for C 4 photosynthesis and occurs via plasmodesmata (PD). Here, we investigated how growth irradiance affects PD density between M and BS cells and between M cells in two C 4 species using our PD quantification method, which combines three‐dimensional laser confocal fluorescence microscopy and scanning electron microscopy. The response of leaf anatomy and physiology of NADP‐ME species, Setaria viridis and Zea mays to growth under different irradiances, low light (100 μmol m ?2 s ?1), and high light (1,000 μmol m ?2 s ?1), was observed both at seedling and established growth stages. We found that the effect of growth irradiance on C 4 leaf PD density depended on plant age and species. The high light treatment resulted in two to four‐fold greater PD density per unit leaf area than at low light, due to greater area of PD clusters and greater PD size in high light plants. These results along with our finding that the effect of light on M‐BS PD density was not tightly linked to photosynthetic capacity suggest a complex mechanism underlying the dynamic response of C 4 leaf PD formation to growth irradiance. 相似文献
3.
C4-like plants represent the penultimate stage of evolution from C3 to C4 plants. Although Coleataenia prionitis (formerly Panicum prionitis) has been described as a C4 plant, its leaf anatomy and gas exchange traits suggest that it may be a C4-like plant. Here, we reexamined the leaf structure and biochemical and physiological traits of photosynthesis in this grass. The large vascular bundles were surrounded by two layers of bundle sheath (BS): a colorless outer BS and a chloroplast-rich inner BS. Small vascular bundles, which generally had a single BS layer with various vascular structures, also occurred throughout the mesophyll together with BS cells not associated with vascular tissue. The mesophyll cells did not show a radial arrangement typical of Kranz anatomy. These features suggest that the leaf anatomy of C. prionitis is on the evolutionary pathway to a complete C4 Kranz type. Phosphoenolpyruvate carboxylase (PEPC) and pyruvate, Pi dikinase occurred in the mesophyll and outer BS. Glycine decarboxylase was confined to the inner BS. Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) accumulated in the mesophyll and both BSs. C. prionitis had biochemical traits of NADP-malic enzyme type, whereas its gas exchange traits were close to those of C4-like intermediate plants rather than C4 plants. A gas exchange study with a PEPC inhibitor suggested that Rubisco in the mesophyll could fix atmospheric CO2. These data demonstrate that C. prionitis is not a true C4 plant but should be considered as a C4-like plant. 相似文献
4.
The ability to concentrate CO 2 around Rubisco allows C 4 crops to suppress photorespiration. However, as phosphoenolpyruvate regeneration requires ATP, the energetic efficiency of the C 4 pathway at low photosynthetic flux densities (PFD) becomes a balancing act between primary fixation and concentration of CO 2 in mesophyll (M) cells, and CO 2 reduction in bundle sheath (BS) cells. At low PFD, retro‐diffusion of CO 2 from BS cells, relative to the rate of bicarbonate fixation in M cells (termed leakiness φ), is known to increase. This paper investigates whether this increase in ? could be explained by incomplete inhibition of photorespiration. The PFD response of φ was measured at various O 2 partial pressures in young Zea mays plants grown at 250 (LL) and 750 µmol m ?2 s ?1 PFD (HL). φ increased at low PFD and was positively correlated with O 2 partial pressure. Low PFD during growth caused BS conductance and interveinal distance to be lower in the LL plants, compared to the HL plants, which correlated with lower φ. Model analysis showed that incomplete inhibition of photorespiration, especially in the HL plants, and an increase in the relative contribution of mitochondrial respiration at low PFD could explain the observed increases in φ. 相似文献
5.
C 4 photosynthesis is a biochemical pathway that operates across mesophyll and bundle sheath (BS) cells to increase CO 2 concentration at the site of CO 2 fixation. C 4 plants benefit from high irradiance but their efficiency decreases under shade, causing a loss of productivity in crop canopies. We investigated shade acclimation responses of Setaria viridis, a model monocot of NADP-dependent malic enzyme subtype, focussing on cell-specific electron transport capacity. Plants grown under low light (LL) maintained CO 2 assimilation rates similar to high light plants but had an increased chlorophyll and light-harvesting-protein content, predominantly in BS cells. Photosystem II (PSII) protein abundance, oxygen-evolving activity and the PSII/PSI ratio were enhanced in LL BS cells, indicating a higher capacity for linear electron flow. Abundances of PSI, ATP synthase, Cytochrome b6f and the chloroplast NAD(P)H dehydrogenase complex, which constitute the BS cyclic electron flow machinery, were also increased in LL plants. A decline in PEP carboxylase activity in mesophyll cells and a consequent shortage of reducing power in BS chloroplasts were associated with a more oxidised plastoquinone pool in LL plants and the formation of PSII – light-harvesting complex II supercomplexes with an increased oxygen evolution rate. Our results suggest that the supramolecular composition of PSII in BS cells is adjusted according to the redox state of the plastoquinone pool. This discovery contributes to the understanding of the acclimation of PSII activity in C 4 plants and will support the development of strategies for crop improvement, including the engineering of C 4 photosynthesis into C 3 plants. 相似文献
7.
Photosynthetic pathway characteristics were studied in nine species of Heliotropium ( sensu lato, including Euploca), using assessments of leaf anatomy and ultrastructure, activities of PEP carboxylase and C 4 acid decarboxylases, and immunolocalization of ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco) and the P‐subunit of glycine decarboxylase (GDC). Heliotropium europaeum, Heliotropium calcicola and Heliotropium tenellum are C 3 plants, while Heliotropium texanum and Heliotropium polyphyllum are C 4 species. Heliotropium procumbens and Heliotropium karwinskyi are functionally C 3, but exhibit ‘proto‐Kranz’ anatomy where bundle sheath (BS) cells are enlarged and mitochondria primarily occur along the centripetal (inner) wall of the BS cells; GDC is present throughout the leaf. Heliotropium convolvulaceum and Heliotropium greggii are C 3–C 4 intermediates, with Kranz‐like enlargement of the BS cells, localization of mitochondria along the inner BS wall and a loss of GDC in the mesophyll (M) tissue. These C 3–C 4 species of Heliotropium probably shuttle photorespiratory glycine from the M to the BS tissue for decarboxylation. Heliotropium represents an important new model for studying C 4 evolution. Where existing models such as Flaveria emphasize diversification of C 3–C 4 intermediates, Heliotropium has numerous C 3 species expressing proto‐Kranz traits that could represent a critical initial phase in the evolutionary origin of C 4 photosynthesis. 相似文献
8.
Abstract In this study the contribution of climatic factors and phylogenetic relationships affecting the geographical distribution of C 3 and C 4 genera of the Cyperaceae in South Africa was investigated. The δ 13C values of herbarium specimens of 68 southern African species from 22 genera and eight tribes were used to assign the species to either the C 3 or C 4 photosynthetic pathway. Geographical distribution data for the Cyperaceae were used to investigate relationships between climatic factors and the number of species and proportional abundance of C 4 species per region. The number of Cyperaceae species per 2° × 2° square across South Africa varied from less than five in the north‐western regions to more than 15 in the south‐western and north‐eastern regions of South Africa where rainfall exceeds 800 mm y ‐1. Of the 68 species investigated, 28 had C 4 photosynthesis and these were scattered among nine genera of four tribes (Cypereae, Scirpeae, Abildgaardieae and Rhyncosporeae). The proportional abundance of C 4 species ranged from 14% in the winter rainfall regions of the south‐west of South Africa to 67% in the summer rainfall areas of the north‐east. The geographical distribution of species was related to their phylogenetic position such that the distributions of C 3 and C 4 species in Cypereae, Scirpeae and Schoeneae was quite distinct. Linear regression analysis showed that the transition temperatures (equal C 3 and C 4 species numbers) for the Cyperaceae were different to those obtained for the Poaceae from the same region. No strong relationships were found between the proportional abundance of C 4 species and other climate factors such as altitude and rainfall. Our analysis of the current geographical distribution of C 4 Cyperaceae in southern Africa in a phylogenetic context suggests that the ecological advantages conferred by the C 4 pathway differ amongst the different plant groups. 相似文献
9.
Photosynthesis in C 3–C 4 intermediates reduces carbon loss by photorespiration through refixing photorespired CO 2 within bundle sheath cells. This is beneficial under warm temperatures where rates of photorespiration are high; however, it is unknown how photosynthesis in C 3–C 4 plants acclimates to growth under cold conditions. Therefore, the cold tolerance of the C 3–C 4 Salsola divaricata was tested to determine whether it reverts to C 3 photosynthesis when grown under low temperatures. Plants were grown under cold (15/10 °C), moderate (25/18 °C) or hot (35/25 °C) day/night temperatures and analysed to determine how photosynthesis, respiration and C 3–C 4 features acclimate to these growth conditions. The CO 2 compensation point and net rates of CO 2 assimilation in cold‐grown plants changed dramatically when measured in response to temperature. However, this was not due to the loss of C 3–C 4 intermediacy, but rather to a large increase in mitochondrial respiration supported primarily by the non‐phosphorylating alternative oxidative pathway (AOP) and, to a lesser degree, the cytochrome oxidative pathway (COP). The increase in respiration and AOP capacity in cold‐grown plants likely protects against reactive oxygen species (ROS) in mitochondria and photodamage in chloroplasts by consuming excess reductant via the alternative mitochondrial respiratory electron transport chain. 相似文献
11.
Question: The relationship between carbon‐13 in soil organic matter and C 3 and C 4 plant abundance is complicated because of differential productivity, litter fall and decomposition. As a result, applying a mass balance equation to δ 13C data from soils cannot be used to infer past C 3 and C 4 plant abundance; only the proportion of carbon derived from C 3 and C 4 plants can be estimated. In this paper, we compare δ 13C of surface soil samples with vegetation data, in order to establish whether the ratio of C 3:C 4 plants (rather than the proportion of carbon from C 3 and C 4 plants) can be inferred from soil δ 13C. Location: The Tsavo National Park, in southeastern Kenya. Methods: We compare vegetation data with δ 13C of organic matter in surface soil samples and derive regression equations relating the δ 13C of soil organic matter to C 3:C 4 plant abundance. We use these equations to interpret δ 13C data from soil profiles in terms of changes in inferred C 3:C 4 plant ratio. We compare our method of interpretation with that derived from a mass balance approach. Results: There was a statistically significant, linear relationship between the δ 13C of organic matter in surface soil samples and the natural logarithm of the ratio of C 3:C 4 plants in the 100m 2 surrounding the soil sample. Conclusions: We suggest that interpretation of δ 13C data from organic matter in soil profiles can be improved by comparing vegetation surveys with δ 13C of organic matter in surface soil samples. Our results suggest that past C 3 plant abundance might be under‐estimated if a mass balance approach is used. 相似文献
12.
Photosynthesis was examined in leaves of Flaveria brownii A. M. Powell, grown under either 14% or 100% full sunlight. In leaves of high light grown plants, the CO 2 compensation point and the inhibition of photosynthesis by 21% O 2 were significantly lower, while activities of ribulose 1,5-bisphosphate carboxylase/oxygenase and various C 4 cycle enzymes were considerably higher than those in leaves grown in low light. Both the CO 2 compensation point and the degree of O 2 inhibition of apparent photosynthesis were relatively insensitive to the light intensity used during measurements with plants from either growth conditions. Partitioning of atmospheric CO 2 between Rubisco of the C 3 pathway and phosphoenolpyruvate carboxylase of the C 4 cycle was determined by exposing leaves to 14CO 2 for 3 to 16 seconds, and extrapolating the labeling curves of initial products to zero time. Results indicated that ~94% of the CO 2 was fixed by the C 4 cycle in high light grown plants, versus ~78% in low light grown plants. Thus, growth of F. brownii in high light increased the expressed level of C 4 photosynthesis. Consistent with the carbon partitioning patterns, photosynthetic enzyme activities (on a chlorophyll basis) in protoplasts from leaves of high light grown plants showed a more C 4-like pattern of compartmentation. Pyruvate, Pi dikinase and phosphoenolpyruvate carboxylase were more enriched in the mesophyll cells, while NADP-malic enzyme and ribulose 1,5-bisphosphate carboxylase/oxygenase were relatively more abundant in the bundle sheath cells of high light than of low light grown plants. Thus, these results indicate that F. brownii has plasticity in its utilization of different pathways of carbon assimilation, depending on the light conditions during growth. 相似文献
14.
C4 plants have a biochemical carbon concentrating mechanism (CCM) that increases CO 2 concentration around ribulose bisphosphate carboxylase oxygenase (Rubisco) in the bundle sheath (BS). Under limiting light, the activity of the CCM generally decreases, causing an increase in leakiness, ( Φ), the ratio of CO 2 retrodiffusing from the BS relative to C4 carboxylation processes. Maize plants were grown under high and low light regimes (respectively HL, 600 versus LL, 100 μE m ?2 s ?1). Short‐term acclimation of Φ was compared from isotopic discrimination (Δ), gas exchange and photochemistry. Direct measurement of respiration in the light, and ATP production rate ( JATP), allowed us use a novel approach to derive Φ, compared with the conventional fitting of measured and predicted Δ. HL grown plants responded to decreasing light intensities with the well‐documented increase in Φ. Conversely, LL plants showed a constant Φ, which has not been observed previously. We explain the pattern by two contrasting acclimation strategies: HL plants maintained a high CCM activity at LL, resulting in high CO 2 overcycling and increased Φ; LL plants acclimated by down‐regulating the CCM, effectively optimizing scarce ATP supply. This surprising plasticity may limit the impact of Φ‐dependent carbon losses in leaves becoming shaded within developing canopies. 相似文献
15.
Intact cells of Flavobacterium dehydrogenans grown on glucose or acetate did not incorporate mevalonic acid-[ 14C]. After treatment with lysozyme the protoplasts were lysed by sonication in a dilute medium containing mevalonic acid-[ 14C] and the cell-free system produced incorporated label into uncyclized C 40, monocyclic C 45 and bicyclic C 50 carotenoids of which decaprenoxanthin was the most abundant.With mevalonate-[2- 14C,4 R-4- 3H 1] the 14C: 3H ratios of the carotenoids showed that the hydrogen atoms at C-2 and C-6 of the ring and that at C-3 of the 1-hydroxy, 2-methyl but-2-ene-4-yl residues of decaprenoxanthin were derived from the 4- pro-R hydrogen atom of mevalonic acid.Mevalonate-[2- 14C,2 R-2- 3H 1] and mevalonate-[2- 14C,2 S-2- 3H 1] gave ratios which showed that the C-4 hydrogen atoms of decaprenoxanthin were derived from the 2- pro-S hydrogen atom of mevalonic acid. 相似文献
16.
Summary This study tested the hypothesis that grasses with the C 4 photosynthetic pathway are avoided as a food source by insect herbivores in natural communities. Insects were sampled from ten pairs of C 3–C 4 grasses and their distributions analyzed by paired comparisons tests. Results showed no statistically significant differences in herbivore utilization of C 3–C 4 species. However, there was a trend towards heavier utilization of C 3 species when means for both plant groups were compared. In particular, Homoptera and Diptera showed heavier usage of C 3 plants. Significant correlations between insect abundances and plant protein levels suggest that herbivores respond to the higher protein content of C 3 grasses. 13C values for six of the most common grasshopper species in the study area indicated that three species fed on C 3 plants, two species fed on C 4 plants, and one species consumed a mixture of C 3 and C 4 tissue.Welder Wildlife Refuge Contribution Number 213 相似文献
17.
Compared with C 3 plants, C 4 plants possess a mechanism to concentrate CO 2 around the ribulose-1,5-bisphosphate carboxylase/oxygenase in chloroplasts of bundle sheath cells so that the carboxylation reaction work at a much more efficient rate, thereby substantially eliminate the oxygenation reaction and the resulting photorespiration. It is observed that C 4 photosynthesis is more efficient than C 3 photosynthesis under conditions of low atmospheric CO 2, heat, drought and salinity, suggesting that these factors are the important drivers to promote C 4 evolution. Although C 4 evolution took over 66 times independently, it is hypothesized that it shared the following evolutionary trajectory: 1) gene duplication followed by neofunctionalization; 2) anatomical and ultrastructral changes of leaf architecture to improve the hydraulic systems; 3) establishment of two-celled photorespiratory pump; 4) addition of transport system; 5) co-option of the duplicated genes into C 4 pathway and adaptive changes of C 4 enzymes. Based on our current understanding on C 4 evolution, several strategies for engineering C 4 rice have been proposed to increase both photosynthetic efficiency and yield significantly in order to avoid international food crisis in the future, especially in the developing countries. Here we summarize the latest progresses on the studies of C 4 evolution and discuss the strategies to introduce two-celled C 4 pathway into rice. 相似文献
18.
Aim The C 4 and crassulacean acid metabolism (CAM) pathways are adaptations to compensate for high rates of photorespiration and water and carbon deficiency. This is the first attempt to compare the relative abundance of C 3 vs. C 4 + CAM species in temperate and subtropical grasslands across a latitudinal gradient in central Argentina. We predict that under the same rainfall regime, C 4 + CAM plants will have larger soil coverage in highly saline soils than in neighbouring non‐saline ones. Location Data were taken from three phytogeographical provinces in the Santa Fe province of Argentina: Chaquenian, Pampean and Espinal. Methods The salinity of the soil was estimated through aqueous solution conductivity. The proportions of species belonging to C 3/C 4 + CAM photosynthetic pathways were compared among halophyte and non‐halophyte communities with a χ 2 homogeneity test. The sum of cover percentages corresponding to the C 3 and C 4 + CAM photosynthetic pathways were calculated and compared using analysis of variance (ANOVA). Results The soil conductivity values were higher in the halophyte than in the non‐halophyte communities for the same phytogeographical area. The C 4 + CAM plants had much higher soil coverage values in halophyte than in non‐halophyte communities in the Pampean and Espinal phytogeographical provinces. The differences were not statistically significant in the Chaquenian province. Main conclusions Soil drought provoked by soil salinity results in a much higher soil cover by C 4 + CAM plants in regions with positive to neutral water balance (i.e. Pampean and Espinal). This differential abundance pattern in C 4 + CAM functional group is not observed in areas where a pronounced water deficit exists per se (Chaquenian region), and therefore C 4 + CAM plants predominate in all environments regardless of soil salinity. Our results suggest that one of the main environmental forces driving the upsurge of C 4 species in Argentinean grasslands might have been the strong local soil salinity gradient. 相似文献
20.
Ecotypic differences in the photosynthetic carbon metabolism of Mollugo verticillata were studied. Variations in C 3 and C 4 cycle activity are apparently due to differences in the activities of enzymes associated with each pathway. Compared to C 4 plants, the activities of C 4 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 C 3 plants, possibly accounting for the high photosynthetic rates of this species. Unlike either C 3 or C 4 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 C 4 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
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