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1.
Abstract. The photosynthetic responses to temperature in C 3, C 3-C 4 intermediate, and C 4 species in the genus Flaveria were examined in an effort to identify whether the reduced photorespiration rates characteristic of C 3-C 4 intermediate photosynthesis result in adaptive advantages at warm leaf temperatures. Reduced photorespiration rates were reflected in lower CO 2 compensation points at all temperatures examined in the C 3-C 4 intermediate, Flaveria floridana, compared to the C 3 species, F. cronquistii. The C 3-C 4 intermediate, F. floridana, exhibited a C 3-like photosynthetic temperature dependence, except for relatively higher photosynthesis rates at warm leaf temperatures compared to the C 3 species, F. cronquistii. Using models of C 3 and C 3-C 4 intermediate photosynthesis, it was predicted that by recycling photorespired CO 2 in bundle-sheath cells, as occurs in many C 3-C 4 intermediates, photosynthesis rates at 35°C could be increased by 28%, compared to a C 3 plant. Without recycling photorespired CO 2, it was calculated that in order to improve photosynthesis rates at 35°C by this amount in C 3 plants, (1) intercellular CO 2 partial pressures would have to be increased from 25 to 31 Pa, resulting in a 57% decrease in water-use efficiency, or (2) the activity of RuBP carboxylase would have to be increased by 32%, resulting in a 22% decrease in nitrogen-use efficiency. In addition to the recycling of photorespired CO 2, leaves of F. floridana appear to effectively concentrate CO 2 at the active site of RuBP carboxylase, increasing the apparent carboxylation efficiency per unit of in vitro RuBP carboxylase activity. The CO 2-concentrating activity also appears to reduce the temperature sensitivity of the carboxylation efficiency in F. floridana compared to F. cronquistii. The carboxylation efficiency per unit of RuBP carboxylase activity decreased by only 38% in F. floridana, compared to 50% in F. cronquistii, as leaf temperature was raised from 25 to 35°C. The C 3-C 4 intermediate, F. ramosissima, exhibited a photosynthetic temperature temperature response curve that was more similar to the C 4 species, F. trinervia, than the C 3 species, F. cronquistii. The C 4-like pattern is probably related to the advanced nature of C 4-like biochemical traits in F. ramosissima The results demonstrate that reductions in photorespiration rates in C 3-C 4 intermediate plants create photosynthetic advantages at warm leaf temperatures that in C 3 plants could only be achieved through substantial costs to water-use efficiency and/or nitrogen-use efficiency. 相似文献
3.
The 2H/ 1H ratio of carbon‐bound H in biolipids holds potential for probing plant lipid biosynthesis and metabolism. The biochemical mechanism underlying the isotopic differences between lipids from C 3 and C 4 plants is still poorly understood. GC‐pyrolysis‐IRMS (gas chromatography‐pyrolysis‐isotope ratio mass spectrometry) measurement of the 2H/ 1H ratio of leaf lipids from controlled and field grown plants indicates that the biochemical isotopic fractionation (ε 2H lipid_biochem) differed between C 3 and C 4 plants in a pathway‐dependent manner: ε 2H C4 > ε 2H C3 for the acetogenic pathway, ε 2H C4 < ε 2H C3 for the mevalonic acid pathway and the 1‐deoxy‐D‐xylulose 5‐phosphate pathway across all species examined. It is proposed that compartmentation of photosynthetic CO 2 fixation into C 4 mesophyll (M) and bundle sheath (BS) cells and suppression of photorespiration in C 4 M and BS cells both result in C 4 M chloroplastic pyruvate – the precursor for acetogenic pathway – being more depleted in 2H relative to pyruvate in C 3 cells. In addition, compartmentation in C 4 plants also results in (i) the transferable H of NADPH being enriched in 2H in C 4 M chloroplasts compared with that in C 3 chloroplasts for the 1‐deoxy‐D‐xylulose 5‐phosphate pathway pathway and (ii) pyruvate relatively 2H‐enriched being used for the mevalonic acid pathway in the cytosol of BS cells in comparison with that in C 3 cells. 相似文献
4.
C 4 photosynthesis is a complex trait resulting from a series of anatomical and biochemical modifications to the ancestral C 3 pathway. It is thought to evolve in a stepwise manner, creating intermediates with different combinations of C 4‐like components. Determining the adaptive value of these components is key to understanding how C 4 photosynthesis can gradually assemble through natural selection. Here, we decompose the photosynthetic phenotypes of numerous individuals of the grass Alloteropsis semialata, the only species known to include both C 3 and C 4 genotypes. Analyses of δ 13C, physiology and leaf anatomy demonstrate for the first time the existence of physiological C 3–C 4 intermediate individuals in the species. Based on previous phylogenetic analyses, the C 3–C 4 individuals are not hybrids between the C 3 and C 4 genotypes analysed, but instead belong to a distinct genetic lineage, and might have given rise to C 4 descendants. C 3 A. semialata, present in colder climates, likely represents a reversal from a C 3–C 4 intermediate state, indicating that, unlike C 4 photosynthesis, evolution of the C 3–C 4 phenotype is not irreversible. 相似文献
5.
C 4 photosynthesis occurs in the most productive crops and vegetation on the planet, and has become widespread because it allows increased rates of photosynthesis compared with the ancestral C 3 pathway. Leaves of C 4 plants typically possess complicated alterations to photosynthesis, such that its reactions are compartmented between mesophyll and bundle sheath cells. Despite its complexity, the C 4 pathway has arisen independently in 62 separate lineages of land plants, and so represents one of the most striking examples of convergent evolution known. We demonstrate that elements in untranslated regions (UTRs) of multiple genes important for C 4 photosynthesis contribute to the metabolic compartmentalization characteristic of a C 4 leaf. Either the 5′ or the 3′ UTR is sufficient for cell specificity, indicating that functional redundancy underlies this key aspect of C 4 gene expression. Furthermore, we show that orthologous PPDK and CA genes from the C 3 plant Arabidopsis thaliana are primed for recruitment into the C 4 pathway. Elements sufficient for M‐cell specificity in C 4 leaves are also present in both the 5′ and 3′ UTRs of these C 3A. thaliana genes. These data indicate functional latency within the UTRs of genes from C 3 species that have been recruited into the C 4 pathway. The repeated recruitment of pre‐existing cis‐elements in C 3 genes may have facilitated the evolution of C 4 photosynthesis. These data also highlight the importance of alterations in trans in producing a functional C 4 leaf, and so provide insight into both the evolution and molecular basis of this important type of photosynthesis. 相似文献
6.
The Chenopodiaceae genus Salsola contains a large number of species with C 4 photosynthesis. Along with derivative genera they have a prominent position among the desert vegetation of Asia and Africa.
About 130 species from Asia and Africa were investigated to determine the occurrence of C 3 versus C 4 syndrome in leaves and cotyledons, and to study specific anatomical and biochemical features of photosynthesis in both photosynthetic
organs. The species studied belong to all six previously identified sections of the tribe Salsoleae based on morphological
characters. Types of photosynthesis were identified using carbon 13C/ 12C isotope fractionation. The representatives of all systematic groups were investigated for mesophyll anatomy and biochemical
subtypes by determination of enzyme activity (RUBPC, PEPC, NAD- and NADP-ME and AAT) and primary photosynthetic products.
Two photosynthetic types (C 3 and C 4) and two biochemical subtypes (NAD- and NADP-ME) were identified in both leaves and cotyledons. Both Kranz and non-Kranz
type anatomy were found in leaves and cotyledons, but cotyledons had more diversity in anatomical structure. Strong relationships
between anatomical types and biochemical subtypes in leaves and cotyledons were shown. We found convincing evidence for a
similar pattern of structural and biochemical features of photosynthesis in leaves and cotyledons within systematic groups,
and evaluated their relevance at the evolutionary level. We identified six groups in tribe Salsoleae with respect to photosynthetic
types and mesophyll structure in leaves and cotyledons. Two separate lineages of biochemical and anatomical evolution within
Salsoleae were demonstrated based on studies of leaves and cotyledons. The sections Caroxylon, Malpighipila, Cardiandra and Belanthera have no C 3 species and only the NAD-ME C 4 subtype has been found in leaves. We suggest the C 4 species in the NADP-ME lineage evolved in Coccosalsola and Salsola sections, and originated in the subsection Arbuscula. Coccosalsola contains many species with C 3 and/or C 3-C 4 intermediate photosynthesis. Within these main evolutionary lineages, species of different taxonomic groups (sections and
subsections) had differences in anatomical or/and biochemical features in leaves and cotyledons. We conclude that structural
and biochemical changes in the photosynthetic apparatus in species of the tribe Salsoleae were a key factor in their evolution
and broad distribution in extreme desert environments.
Received January 25, 2001 Accepted July 17, 2001 相似文献
7.
In Panicum species of the Laxa group, some of which have characteristics intermediate to C 3 and C 4 photosynthesis species, some mitochondria in leaf bundle sheath cells are surrounded by chloroplasts when viewed in profile. Serial sectioning of leaves of one Laxa species, Panicum schenckii Hack, shows that these mitochondria are enclosed by chloroplasts. Complete enclosure rather than invagination also is indicated by absence of two concentric chloroplast membranes surrounding the mitochondrial profiles. 相似文献
9.
The Chenopodiaceae is one of the families including C4 species among eudicots. In this family, the genus Chenopodium is considered to include only C3 species. However, we report here a transition from C3 photosynthesis to proto-Kranz to C3–C4 intermediate type in Chenopodium. We investigated leaf anatomical and photosynthetic traits of 15 species, of which 8 species showed non-Kranz anatomy and a CO2 compensation point (Γ) typical of C3 plants. However, 5 species showed proto-Kranz anatomy and a C3-like Γ, whereas C. strictum showed leaf anatomy and a Γ typical of C3–C4 intermediates. Chenopodium album accessions examined included both proto-Kranz and C3–C4 intermediate types, depending on locality. Glycine decarboxylase, a key photorespiratory enzyme that is involved in the decarboxylation of glycine, was located predominantly in the mesophyll (M) cells of C3 species, in both M and bundle-sheath (BS) cells in proto-Kranz species, and exclusively in BS cells in C3–C4 intermediate species. The M/BS tissue area ratio, number of chloroplasts and mitochondria per BS cell, distribution of these organelles to the centripetal region of BS cells, the degree of inner positioning (vacuolar side of chloroplasts) of mitochondria in M cells, and the size of BS mitochondria also changed with the change in glycine decarboxylase localization. All Chenopodium species examined were C3-like regarding activities and amounts of C3 and C4 photosynthetic enzymes and δ13C values, suggesting that these species perform photosynthesis without contribution of the C4 cycle. This study demonstrates that Chenopodium is not a C3 genus and is valuable for studying evolution of C3–C4 intermediates. 相似文献
10.
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
11.
Background and AimsCleomaceae is one of 19 angiosperm families in which C 4 photosynthesis has been reported. The aim of the study was to determine the type, and diversity, of structural and functional forms of C 4 in genus Cleome.MethodsPlants of Cleome species were grown from seeds, and leaves were subjected to carbon isotope analysis, light and scanning electron microscopy, western blot analysis of proteins, and in situ immunolocalization for ribulose bisphosphate carboxylase oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC). Key ResultsThree species with C 4-type carbon isotope values occurring in separate lineages in the genus ( Cleome angustifolia, C. gynandra and C. oxalidea) were shown to have features of C 4 photosynthesis in leaves and cotyledons. Immunolocalization studies show that PEPC is localized in mesophyll (M) cells and Rubisco is selectively localized in bundle sheath (BS) cells in leaves and cotyledons, characteristic of species with Kranz anatomy. Analyses of leaves for key photosynthetic enzymes show they have high expression of markers for the C 4 cycle (compared with the C 3–C 4 intermediate C. paradoxa and the C 3 species C. africana). All three are biochemically NAD-malic enzyme sub-type, with higher granal development in BS than in M chloroplasts, characteristic of this biochemical sub-type. Cleome gynandra and C. oxalidea have atriplicoid-type Kranz anatomy with multiple simple Kranz units around individual veins. However, C. angustifolia anatomy is represented by a double layer of concentric chlorenchyma forming a single compound Kranz unit by surrounding all the vascular bundles and water storage cells. ConclusionsNAD-malic enzyme-type C 4 photosynthesis evolved multiple times in the family Cleomaceae, twice with atriplicoid-type anatomy in compound leaves having flat, broad leaflets in the pantropical species C. gynandra and the Australian species C. oxalidea, and once by forming a single Kranz unit in compound leaves with semi-terete leaflets in the African species C. angustifolia. The leaf morphology of C. angustifolia, which is similar to that of the sister, C 3–C 4 intermediate African species C. paradoxa, suggests adaptation of this lineage to arid environments, which is supported by biogeographical information. 相似文献
12.
Immediate export in leaves of C 3‐C 4 intermediates were compared with their C 3 and C 4 relatives within the Panicum and Flaveria genera. At 35 Pa CO 2, photosynthesis and export were highest in C 4 species in each genera. Within the Panicum, photosynthesis and export in ‘type I’ C 3‐C 4 intermediates were greater than those in C 3 species. However, ‘type I’ C 3‐C 4 intermediates exported a similar proportion of newly fixed 14C as did C 4 species. Within the Flaveria, ‘type II’ C 3‐C 4 intermediate species had the lowest export rather than the C 3 species. At ambient CO 2, immediate export was strongly correlated with photosynthesis. However, at 90 Pa CO 2, when photosynthesis and immediate export increased in all C 3 and C 3‐C 4 intermediate species, proportionally less C was exported in all photosynthetic types than that at ambient CO 2. All species accumulated starch and sugars at both CO 2 levels. There was no correlation between immediate export and the pattern of 14C‐labelling into sugars and starch among the photosynthetic types within each genus. However, during CO 2 enrichment, C 4Panicum species accumulated sugars above the level of sugars and starch normally made at ambient CO 2, whereas the C 4Flaveria species accumulated only additional starch. 相似文献
13.
Images of chlorophyll fluorescence emitted at wavelengths above and below 700 nm were recorded from leaf sections of C 4 species using confocal laser scanning microscopy (LSM). We investigated species exhibiting both NAD-malic enzyme (NAD-ME) C 4 photosynthesis and NADP-malic enzyme (NADP-ME) C 4 photosynthesis. Comparing LSM fluorescence of leaf sections with flow-cytometrically determined fluorescence from individual chloroplasts revealed that LSM fluorescence was distorted by the optical properties of leaf sections. Leaf section fluorescence, when corrected by transmission data derived from light transmission images, agreed with flow cytometry data. The corrected LSM fluorescence yielded information on the distribution of the individual photosystems in the C 4 leaf sections: PSII concentrations in bundle sheath cells were elevated in NAD-ME species but diminished in most of the NADP-ME species investigated. The NADP-ME species, Arundinella hirta, however, showed normal PSII and increased PSI concentration in bundle sheath chloroplasts. Finally, a gradient of PSI was observed within the bundle sheath cells from Euphorbia maculata. 相似文献
14.
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
15.
Abstract Models developed to explain the biphasic response of CO 2 compensation concentration to O 2 concentration and the C 3-like carbon isotope discrimination in C 3-C 4 intermediate species are used to characterize quantitatively the steps necessary in the evolution of C 4 photosynthesis. The evolutionary stages are indicated by model outputs, CO 2 compensation concentration and δ 13C value. The transition from intermediate plants to C 4 plants requires the complete formation of C 4 cycle capacity, expressed by the models as transition from C 4 cycle limitation by phosphoenolpyruvate (PEP) regeneration rate to limitation by PEP carboxylase activity. Other steps refer to CO 2 leakage from bundle sheath cells, to further augmentations of C 4 cycle components, to the repression of ribulose-1,5-bisphos-phate carboxylase in the mesophyll cells, and to a decrease in the CO 2 affinity of the enzyme. Possibilities of extending the suggested approach to other physiological characteristics, and the adaptive significance of the steps envisaged, are discussed. 相似文献
16.
Global climate change is expected to shift regional rainfall patterns, influencing species distributions where they depend on water availability. Comparative studies have demonstrated that C 4 grasses inhabit drier habitats than C 3 relatives, but that both C 3 and C 4 photosynthesis are susceptible to drought. However, C 4 plants may show advantages in hydraulic performance in dry environments. We investigated the effects of seasonal variation in water availability on leaf physiology, using a common garden experiment in the Eastern Cape of South Africa to compare 12 locally occurring grass species from C 4 and C 3 sister lineages. Photosynthesis was always higher in the C 4 than C 3 grasses across every month, but the difference was not statistically significant during the wettest months. Surprisingly, stomatal conductance was typically lower in the C 3 than C 4 grasses, with the peak monthly average for C 3 species being similar to that of C 4 leaves. In water‐limited, rain‐fed plots, the photosynthesis of C 4 leaves was between 2.0 and 7.4 μmol m ?2 s ?1 higher, stomatal conductance almost double, and transpiration 60% higher than for C 3 plants. Although C 4 average instantaneous water‐use efficiencies were higher (2.4–8.1 mmol mol ?1) than C 3 averages (0.7–6.8 mmol mol ?1), differences were not as great as we expected and were statistically significant only as drought became established. Photosynthesis declined earlier during drought among C 3 than C 4 species, coincident with decreases in stomatal conductance and transpiration. Eventual decreases in photosynthesis among C 4 plants were linked with declining midday leaf water potentials. However, during the same phase of drought, C 3 species showed significant decreases in hydrodynamic gradients that suggested hydraulic failure. Thus, our results indicate that stomatal and hydraulic behaviour during drought enhances the differences in photosynthesis between C 4 and C 3 species. We suggest that these drought responses are important for understanding the advantages of C 4 photosynthesis under field conditions. 相似文献
17.
The amphibious leafless sedge, Eleocharis baldwinii, expresses C 4 characteristics in the terrestrial form and intermediate characteristics between C 3 and C 4 photosynthesis in the submerged form. This study examined the immunocytochemical localization of C 3 and C 4 enzymes in culms of the two forms to elucidate the regulatory mechanism of photosynthetic metabolism and compared the activities and amounts of C 3 and C 4 enzymes with those in other Eleocharis species, E. vivipara and E. retroflexa, which show C 4 characteristics on land but C 3 and C 4 characteristics under water. The terrestrial form of E. baldwinii exhibited a C 4‐like pattern of enzyme localization. The submerged form exhibited a modified anatomy with well‐developed mesophyll cells and small Kranz cells. The C 4 enzyme levels declined conspicuously in outer mesophyll cells adjacent to the epidermis, whereas Rubisco levels increased throughout the mesophyll in the submerged form. These results suggest that intermediate photosynthesis between C 3 and C 4 photosynthesis in the submerged form results from the predominant operation of the C 3 pathway in the outer mesophyll cells and the C 4 pathway in both the inner mesophyll and Kranz cells. Differences in the degree of C 4 expression in terrestrial forms of Eleocharis species may cause the differences in the expression of photosynthetic modes under water. 相似文献
18.
The biochemistry and leaf anatomy of plants using C 4 photosynthesis promote the concentration of atmospheric CO 2 in leaf tissue that leads to improvements in growth and yield of C 4 plants over C 3 species in hot, dry, high light, and/or saline environments. C 4 plants like maize and sugarcane are significant food, fodder, and bioenergy crops. The C 4 photosynthetic pathway is an excellent example of convergent evolution, having evolved in multiple independent lineages of land plants from ancestors employing C 3 photosynthesis. In addition to C 3 and C 4 species, some plant lineages contain closely related C 3–C 4 intermediate species that demonstrate leaf anatomical, biochemical, and physiological characteristics between those of C 3 plants and species using C 4 photosynthesis. These groups of plants have been extremely useful in dissecting the modifications to leaf anatomy and molecular biology, which led to the evolution of C 4 photosynthesis. It is now clear that great variation exists in C 4 leaf anatomy, and diverse molecular mechanisms underlie C 4 biochemistry and physiology. However, all these different paths have led to the same destination—the expression of a C 4 CO 2 concentrating mechanism. Further identification of C 4 leaf anatomical traits and molecular biological components, and understanding how they are controlled and assembled will not only allow for additional insights into evolutionary convergence, but also contribute to sustainable food and bioenergy production strategies. 相似文献
19.
Sequence comparisons have shown that nucleotide sequences of the H-protein, a component of the glycine cleavage system, are only moderately conserved and can be used as molecular markers for intrageneric phylogenetic studies. We have analysed the respective cDNA sequences from 12 species of Flaveria, and a more limited set of gdcsH upstream regions. These data are discussed with respect to a phylogenetic reconstruction of Flaveria, a small genus which includes species of different photo-synthetic types, namely C 3, C 3-C 4, C 4-like and C 4. Our analysis essentially supports an earlier hypothesis, based on morphological and eco-geographical data, of the evolution of Flaveria (Powell 1978). This close agreement shows the usefulness of H-protein nucleotide sequences at a low taxonomic level. Our analysis independently confirms that C 4 photosynthesis has evolved two times in different lineages of Flaveria. Most remarkably, the C 4 taxa of Flaveria appear as derived relative to the C 3-C 4 intermediate taxa, i.e. they probably have common direct predecessors. This is the first direct evidence for a phylo-genetically intermediate position of C 3-C 4 intermediate photosynthesis. Our data also confirm the antiquity of C 3 photosynthesis in Flaveria but suggest that the collection of F. pringlei used in our experiments, although clearly of C 3 photosynthetic metabolism, possibly originated from hybridization with a more advanced taxon. 相似文献
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