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1.
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
2.
The genus Flaveria shows evidence of evolution in the mechanism of photosynthesis as its 21 species include C 3, C 3-C 4, C 4-like, and C 4 plants. In this study, several physiological and biochemical parameters of photosynthesis and photorespiration were measured in 18 Flaveria species representing all the photosynthetic types. The 10 species classified as C 3-C 4 intermediates showed an inverse continuum in level of photorespiration and development of the C 4 syndrome. This ranges from F. sonorensis with relatively high apparent photorespiration and lacking C 4 photosynthesis to F. Among the intermediates, the photosynthetic CO2 compensation points at 30°C and 1150 micromoles quanta per square meter per second varied from 9 to 29 microbars. The values for the three C 4-like species varied from 3 to 6 microbars, similar to those measured for the C 4 species. The activities of the photorespiratory enzymes glycolate oxidase, hydroxypyruvate reductase, and serine hydroxymethyltransferase decreased progressively from C 3 to C 3-C 4 to C 4-like and C 4 species. On the other hand, most intermediates had higher levels of phosph enolpyruvate carboxylase and NADP-malic enzyme than C 3 species, but generally lower activities compared to C 4-like and C 4 species. The levels of these C 4 enzymes are correlated with the degree of C 4 photosynthesis, based on the initial products of photosynthesis. Another indication of development of the C 4 syndrome in C 3-C 4 Flaveria species was their intermediate chlorophyll a/b ratios. The chlorophyll a/b ratios of the various Flaveria species are highly correlated with the degree of C 4 photosynthesis suggesting that the photochemical machinery is progressively altered during evolution in order to meet the specific energy requirements for operating the C 4 pathway. In the progression from C 3 to C 4 species in Flaveria, the CO 2 compensation point decreased more rapidly than did the decrease in O 2 inhibition of photosynthesis or the increase in the degree of C 4 photosynthesis. These results suggest that the reduction in photorespiration during evolution occurred initially by refixation of photorespired CO 2 and prior to substantive reduction in O 2 inhibition and development of the C 4 syndrome. However, further reduction in O 2 inhibition in some intermediates and C 4-like species is considered primarily due to the development of the C 4 syndrome. Thus, the evolution of C 3-C 4 intermediate photosynthesis likely occurred in response to environmental conditions which limit the intercellular CO 2 concentration first via refixation of photorespired CO 2, followed by development of the C 4 syndrome. 相似文献
3.
The vast majority of angiosperms, including most of the agronomically important crop plants (wheat, etc.), assimilate CO 2 through the inefficient C 3 pathway of photosynthesis. Under ambient conditions these organisms loose about 1/3 of fixed carbon via photorespiration, an energetically wasteful process. Plants with C 4 photosynthesis (such as maize) eliminate photorespiration via a biochemical CO 2-pump and thus have a larger rate of carbon gain. The genus Flaveria (yellowtops, Asteraceae) contains not only C 3 and C 4 species, but also many C 3-C 4 intermediates, which have been interpreted as evolving from C 3 to fully expressed C 4 metabolism. However, the evolutionary significance of C 3-C 4Flaveria-intermediates has long been a matter of debate. A well-resolved phylogeny of nearly all Flaveria species has recently been published. Here, we review pertinent background information and combine this novel phylogeny with physiological data. We conclude that the Flaveria species complex provides a robust model system for the study of the transition from C 3 to C 4 photosynthesis, which is arguably a macroevolutionary event. We conclude with comments relevant to the current Intelligent Design debate. 相似文献
4.
Ultrastructural studies of leaves of seven Panicum species in or closely related to the Laxa group and classified as C 3, C 4 or C 3-C 4 intermediate were undertaken to examine features associated with C 3 and C 4 photosynthesis. The C 3 species Panicum rivulare Trin. had few organelles in bundle sheath cell profiles (2 chloroplasts, 1.1 mitochondria, and 0.3 peroxisomes per cell section) compared to an average of 10.6 chloroplasts, 17.7 mitochondria, and 3.2 peroxisomes per bundle sheath cell profile for three C 3-C 4 species, Panicum milioides Nees ex Trin., Panicum decipiens Nees ex Trin. and Panicum schenckii Hack. However, two other C 3 species, Panicum laxum Sw. and Panicum hylaeicum Mez, contained about 0.7, 0.5, and 0.3 as many chloroplasts, mitochondria, and peroxisomes, respectively, as in bundle sheath cell profiles of the C 3-C 4 species. Chloroplasts and mitochondria in bundle sheath cells were larger than those in mesophyll cells for the C 4 species Panicum prionitis Griseb. and the C 3-C 4 species, but in C 3 species the organelles were similar in size or were smaller in the bundle sheath cells. The C 3-C 4 species and P. laxum and P. hylaeicum exhibited an unusually close association of organelles in bundle sheath cells with mitochondria frequently surrounded in profile by chloroplasts. The high concentrations in bundle sheath cells of somewhat larger organelles than in mesophyll cells correlates with the reduced photorespiration of the C 3-C 4 species. 相似文献
5.
Background and AimsLeaf venation in many C 4 species is characterized by high vein density, essential in facilitating rapid intercellular diffusion of C 4 photosynthetic metabolites between different tissues (mesophyll, bundle sheath). Greater vein density has been hypothesized to be an early step in C 4 photosynthesis evolution. Development of C 4 vein patterning is thought to occur from either accelerated or prolonged procambium formation, relative to ground tissue development. MethodsCleared and sectioned tissues of phylogenetically basal C 3 Flaveria robusta and more derived C 4 Flaveria bidentis were compared for vein pattern in mature leaves and vein pattern formation in developing leaves. Key ResultsIn mature leaves, major vein density did not differ between C 3 and C 4 Flaveria species, whereas minor veins were denser in C 4 species than in C 3 species. The developmental study showed that both major and minor vein patterning in leaves of C 3 and C 4 species were initiated at comparable stages (based on leaf length). An additional vein order in the C 4 species was observed during initiation of the higher order minor veins compared with the C 3 species. In the two species, expansion of bundle sheath and mesophyll cells occurred after vein pattern was complete and xylem differentiation was continuous in minor veins. In addition, mesophyll cells ceased dividing sooner and enlarged less in C 4 species than in C 3 species. ConclusionsLeaf vein pattern characteristic to C 4 Flaveria was achieved primarily through accelerated and earlier offset of higher order vein formation, rather than other modifications in the timing of vein pattern formation, as compared with C 3 species. Earlier cessation of mesophyll cell division and reduced expansion also contributed to greater vein density in the C 4 species. The relatively late expansion of bundle sheath and mesophyll cells shows that vein patterning precedes ground tissue development in C 4 species.Key words: Bundle sheath, C4 photosynthesis evolution, Flaveria, heterochrony, leaf development, mesophyll, vein density, vein pattern formation 相似文献
6.
Stomatal function mediates physiological trade‐offs associated with maintaining a favourable H 2O balance in leaf tissues while acquiring CO 2 as a photosynthetic substrate. The C 3 and C 4 species appear to have different patterns of stomatal response to changing light conditions, and variation in this behaviour may have played a role in the functional diversification of the different photosynthetic pathways. In the current study, we used gain analysis theory to characterize the stomatal conductance response to light intensity in nine different C 3, C 4 and C 3‐C 4 intermediate species Flaveria species. The response of stomatal conductance ( gs) to a change in light intensity represents both a direct (related to a change in incident light intensity, I) and indirect (related to a change in intercellular CO 2 concentration, Ci) response. The slope of the line relating the change in gs to Ci was steeper in C 4 species, compared with C 3 species, with C 3‐C 4 species having an intermediate response. This response reflects the greater relative contribution of the indirect versus direct component of the gs versus I response in the C 4 species. The C 3‐C 4 species, Flaveria floridana, exhibited a C 4‐like response whereas the C 3‐C 4 species, Flaveria sonorensis and Flaveria chloraefolia, exhibited C 3‐like responses, similar to their hypothesized position along the evolutionary trajectory of the development of C 4 photosynthesis. There was a positive correlation between the relative contribution of the indirect component of the gs versus I response and water use efficiency when evaluated across all species. Assuming that the C 3‐C 4 intermediate species reflect an evolutionary progression from fully expressed C 3 ancestors, the results of the current study demonstrate an increase in the contribution of the indirect component of the gs versus I response as taxa evolve toward the C 4 extreme. The greater relative contribution of the indirect component of the stomatal response occurs through both increases in the indirect stomatal components and through decreases in the direct. Increases in the magnitude of the indirect component may be related to the maintenance of higher water use efficiencies in the intermediate evolutionary stages, before the appearance of fully integrated C 4 photosynthesis. 相似文献
7.
Summary The nature of the photosynthetic pathways of Cyperaceae found in Japan were investigated on the basis of Kranz anatomy, the CO 2 compensation concentration and previously reported data. Among 301 species (96% of all cyperaceous species recorded in the region), 58 species were classified as being C 4 plants. These C 4 species were scattered among the tribes Fimbristylideae, Lipocarpheae, Cypereae and Rhynchosporeae in the subfamily Cyperoideae. The genera Cyperus, Eleocharis and Rhynchospora included, in Japan, both C 3 and C 4 species within a single genus. Using these data, an analysis was made of the ecological characteristics and geographical distribution of the C 3 and C 4 species in Japan. Although cyperaceous species grow in markedly different environments, the majority were found in wet and aquatic areas (61%) or shaded areas, such as forest floors (20%). Most of the C 3 species were also hygrophytes (58%) and forest-living species (25%), and C 3 species growing in mesic and dry areas were relatively rare. The C 4 species inhabited wet and aquatic (75%), mesic (13%) and dry areas (6%) and showed marked ecological characteristics with respect to soil-moisture conditions, unlike other C 4 plants, although they were absent from shaded habitats. In order to determine the climatic factors that influence the relative floristic abundance of C 3 and C 4 members of the Cyperaceae in Japan, the ratios of number of C 4 species to the total number of members of Cyperaceae (C 4 percentage) in 16 representative locales were examined in terms of various climatic variables. There were strong positive correlations between the C 4 percentage and temperature. Among the C 3 groups of three subfamilies, there were different distributional trends for various temperature regimes. The C 3 subfamily Caricoideae increased its relative contribution to the cyperaceous flora with a decrease in mean annual temperature, while the C 3 subfamily Sclerioideae exhibited the opposite pattern. The C 3 group of the subfamily Cyperoideae did not show any marked change in pattern along temperature gradients, unlike the two other C 3 subfamilies, and seemed to be heterogeneous in terms of its response to temperature. The relationships between the C 4 biochemical subtypes and ecological characteristics are also discussed. 相似文献
8.
The aquatic monocot Hydrilla verticillata (L.f.) Royle is a well-documented facultative C 4 NADP-malic enzyme species in which the C 4 and Calvin cycles operate in the same cell with the specific carboxylases confined to the cytosol and chloroplast, respectively. Several key components had already been characterized at the molecular level, thus the purpose of this study was to begin to identify other, less obvious, elements that may be necessary for a functional single-cell C 4 system. Using differential display, mRNA populations from C 3 and C 4 H. verticillata leaves were screened and expression profiles compared. From this study, 65 clones were isolated and subjected to a customized macroarray analysis; 25 clones were found to be upregulated in C 4 leaves. Northern and semi-quantitative RT-PCR analyses were used for confirmation. From these screenings, 13 C 4 upregulated genes were identified. Among these one encoded a previously recognized C 4 phospho enolpyruvate carboxylase, and two encoded distinct pyruvate orthophosphate dikinase isoforms, new findings for H. verticillata. Genes that encode a transporter, an aminotransferase and two chaperonins were also upregulated. Twelve false positives, mostly housekeeping genes, were determined from the Northern/semi-quantitative RT-PCR analyses. Sequence data obtained in this study are listed in the dbEST database (DV216698 to DV216767). As a single-cell C 4 system that lacks Kranz anatomy, a better understanding of how H. verticillata operates may facilitate the design of a transgenic C 4 system in a C 3 crop species.Srinath K. Rao and Hiroshi Fukayama contributed equally to this study. 相似文献
9.
The potential for C 4 photosynthesis was investigated in five C 3-C 4 intermediate species, one C 3 species, and one C 4 species in the genus Flaveria, using 14CO 2 pulse- 12CO 2 chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating 14CO 2 into the C 4 acids malate and aspartate, following an 8-s pulse. The proportion of 14C label in these C 4 products ranged from 50–55% to 20–26% in the C 3-C 4 intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, 14CO 2 into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C 4 photosynthesis among the intermediate species based on the apparent rate of conversion of 14C label from the C 4 cycle to the C 3 cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C 4-cycle products and an increase in percentage label in C 3-cycle products during chase periods with 12CO 2, although the rate of change was slower than in the C 4 species, F. palmeri. In these C 3-C 4 intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C 3-C 4 intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C 4-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C 4 and C 3 cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C 3 species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C 4-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O 2, the absorbed quantum yields for CO 2 uptake (in mol CO 2·[mol quanta] -1) averaged 0.053 in F. cronquistii (C 3), 0.051 in F. trinervia (Spreng.) Mohr (C 4), 0.052 in F. ramosissima (C 3-C 4), 0.051 in F. anomala (C 3-C 4), 0.050 in F. linearis (C 3-C 4), 0.046 in F. floridana (C 3-C 4), and 0.044 in F. pubescens (C 3-C 4). In 2% O 2 an enhancement of the quantum yield was observed in all of the C 3-C 4 intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O 2 were intermediate in value to the C 3 and C 4 species, indicating a co-function of the C 3 and C 4 cycles in CO 2 assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O 2 presumably reflect an ineffcient transfer of carbon from the C 4 to the C 3 cycle. The response of the quantum yield to four increasing O 2 concentrations (2–35%) showed lower levels of O 2 inhibition in the C 3-C 4 intermediate F. ramosissima, relative to the C 3 species. This indicates that the co-function of the C 3 and C 4 cycles in this intermediate species leads to an increased CO 2 concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O 2.Abbreviations PEP
phosphoenolpyruvate
- PGA
3-phosphoglycerate
- RuBP
ribulose-1,5-bisphosphate 相似文献
10.
During the last Ice age, CO2 concentration ([CO2]) was 180-200 μmol/mol compared with the modern value of 380 μmol/mol,and global temperatures were ~8 ℃ cooler. Relatively little is known about the responses of C3 and C4 species to longterm exposure to glacial conditions. Here Abutilon theophrasti Medik. (C3) and Amaranthus retroflexus L. (C4) were grown at 200 μmol/mol CO2 with current (30/24 ℃) and glacial (22/16 ℃) temperatures for 22 d. Overall, the C4 species exhibited a large growth advantage over the C3 species at low [CO2]. However, this advantage was reduced at low temperature, where the C4 species produced 5× the total mass of the C3 species versus 14× at the high temperature.This difference was due to a reduction In C4 growth at low temperature, since the C3 species exhibited similar growth between temperatures. Physiological differences between temperatures were not detected for either species, although photorespirationlnet photosynthesis was reduced in the C3 species grown at low temperature, suggesting evidence of improved carbon balance at this treatment. This system suggests that C4 species had a growth advantage over C3 species during low [CO2] of the last ice age, although concurrent reductions in temperatures may have reduced this advantage. 相似文献
11.
Environmental conditions that promote photorespiration are considered to be a major driving force for the evolution of C 4 species from C 3 ancestors. The genus Flaveria contains C 3 and C 4 species as well as a variety of intermediate species. In this study, we compare the water-use efficiency of intermediate
Flaveria species to that of C 3 and C 4 species. The results indicate that under both well-watered and a drought-stress condition, C 3–C 4 and C 4-like intermediacy in Flaveria species improve water-use efficiency as compared to C 3 species. 相似文献
12.
Floristic compositions, life forms, reproductive types for forage species, and their responses to desertification in Hunshandake desert were studied. 164 species, in 30 families and 94 genera, were identified with C 3 (137 species), C 4 (25 species), and CAM (2 species) photosynthesis. Of the 25 C 4 species, 76 % were grasses and Chenopodiaceae species (hereafter chenopods). This suggests that the C 4 species mainly occurred in a few families in the desert region. The reduction of C 3 species and the increase of C 4 species with desertification indicated that C 4 species might have higher tolerance to environmental stresses ( e.g. dry and poor soil). Relatively more hemicrytophyte and therophyte forms in the desert are related to the local temperate climate and vegetation dynamics. Relatively greater proportions of C 4/C 3 and clonal species/sexual species at mobile dune showed that the C 4 species and clonal species could make greater contribution to sand land restoration in the Hunshandake desert. 相似文献
13.
Summary Analyses of carbon-assimilation patterns in response to intercellular CO 2 concentrations, and the photosynthetic water-and nitrogen-use efficiencies, were conducted for a C 3, a C 4, and three C 3–C 4 species in the genus Flaveria in order to determine some of the advantages and disadvantages of C 3–C 4 intermediate photosynthesis. Operational intercellular CO 2 partial pressures (pi), determined when the atmospheric CO 2 partial pressure (pa) was approximately 330 bar, in the C 3–C 4 species were generally equal to, or greater than, those observed in the C 3 species under well-watered or water-stressed conditions. This reflects equal, or lower, water-use efficiencies (WUEs) in the C 3–C 4 species. The only case in which higher WUEs were observed in the C 3–C 4 species, compared to the C 3 species, was when photosynthesis rates were limited by available nitrogen and were less than 12.5 mol CO 2 m -2s -1. At higher photosynthesis rates, the C 3–C 4 species exhibited lower values of photosynthesis rate for equal values of stomatal conductance (lower WUE), compared to the C 3 species. Comparing slopes for the linear regions of the relationship between leaf nitrogen content and net photosynthesis rate (taken as an index of photosynthetic nitrogen-use efficiency, NUE), the C 4 species exhibited the highest NUE, followed by the C 3–C 4 species, F. ramosissima, with the other two C 3–C 4 species and the C 3 species being equal and exhibiting the lowest NUEs. The lack of consistent advantages in NUE and WUE in the C 3–C 4 species F. pubescens and F. floridana suggest that in some C 3–C 4
Flaveria species C 4-like anatomy and biochemistry do not provide the same gas exchange advantages that we typically attribute to the CO 2-concentrating mechanism of fully-expressed C 4 plants. 相似文献
14.
C 3 photosynthesis is an inefficient process, because the enzyme that lies at the heart of the Benson–Calvin cycle, ribulose 1,5-bisphosphate carboxylase-oxygenase (Rubisco) is itself a very inefficient enzyme. The oxygenase activity of Rubisco is an unavoidable side reaction that is a consequence of its reaction mechanism. The product of oxygenation, glycollate 2-P, has to be retrieved by photorespiration, a process which results in the loss of a quarter of the carbon that was originally present in glycollate 2-P. Photorespiration therefore reduces carbon gain. Purely in terms of carbon economy, there is, therefore, a strong selection pressure on plants to reduce the rate of photorespiration so as to increase carbon gain, but it also improves water- and nitrogen-use efficiency. Possibilities for the manipulation of plants to decrease the amount of photorespiration include the introduction of improved Rubisco from other species, reconfiguring photorespiration, or introducing carbon-concentrating mechanisms, such as inorganic carbon transporters, carboxysomes or pyrenoids, or engineering a full C 4 Kranz pathway using the existing evolutionary progression in C 3–C 4 intermediates as a blueprint. Possible routes and progress to suppressing photorespiration by introducing C 4 photosynthesis in C 3 crop plants will be discussed, including whether single cell C 4 photosynthesis is feasible, how the evolution of C 3–C 4 intermediates can be used as a blueprint for engineering C 4 photosynthesis, which pathway for the C 4 cycle might be introduced and the extent to which processes and structures in C 3 plant might require optimisation. 相似文献
15.
The use of mesophyll protoplast extracts from various C 4 species has provided an effective method for studying light-and substrate-dependent formation of oxaloacetate, malate, and asparate at rates equivalent to whole leaf C 4 photosynthesis. Conditions regulating the formation of the C 4 acids were studied with protoplast extracts from Digitaria sanguinalis, an NADP-malic enzyme C 4 species, Eleusineindica, an NAD-malic enzyme C 4 species, and Urochloa panicoides, a phosphoenolpyruvate (PEP) carboxykinase C 4 species. Light-dependent induction of CO 2 fixation by the mesophyll extracts of all three species was relatively low without addition of exogenous substrates. Pyruvate, alanine and α-ketoglutarate, or 3-phosphoglycerate induced high rates of CO 2 fixation in the mesophyll extracts with oxaloacetate, malate, and aspartate being the primary products. In all three species, it appears that pyruvate, alanine, or 3-phosphoglycerate may serve as effective precursors to the formation of PEP for carboxylation through PEP-carboxylase in C 4 mesophyll cells. Induction by pyruvate or alanine and α-ketoglutarate was light-dependent, whereas 3-phosphoglycerate-induced CO 2 fixation was not. 相似文献
16.
Plants using the C 4 photosynthetic pathway have greater water use efficiency (WUE) than C 3 plants of similar ecological function. Consequently, for equivalent rates of photosynthesis in identical climates, C 4 plants do not need to acquire and transport as much water as C 3 species. Because the structure of xylem tissue reflects hydraulic demand by the leaf canopy, a reduction in water transport requirements due to C 4 photosynthesis should affect the evolution of xylem characteristics in C 4 plants. In a comparison of stem hydraulic conductivity and vascular anatomy between eight C 3 and eight C 4 herbaceous species, C 4 plants had lower hydraulic conductivity per unit leaf area ( KL) than C 3 species of similar life form. When averages from all the species were pooled together, the mean KL for the C 4 species was 1.60 × 10 ?4 kg m ?1 s ?1 MPa ?1, which was only one‐third of the mean KL of 4.65 × 10 ?4 kg m ?1 s ?1 MPa ?1 determined for the C 3 species. The differences in KL between C 3 and C 4 species corresponded to the two‐ to three‐fold differences in WUE observed between C 3 and C 4 plants. In the C 4 species from arid regions, the difference in KL was associated with a lower hydraulic conductivity per xylem area, smaller and shorter vessels, and less vulnerable xylem to cavitation, indicating the C 4 species had evolved safer xylem than the C 3 species. In the plants from resource‐rich areas, such as the C 4 weed Amaranthus retroflexus, hydraulic conductivity per xylem area and xylem anatomy were similar to that of the C 3 species, but the C 4 plants had greater leaf area per xylem area. The results indicate the WUE advantage of C 4 photosynthesis allows for greater flexibility in hydraulic design and potential fitness. In resource‐rich environments in which competition is high, an existing hydraulic design can support greater leaf area, allowing for higher carbon gain, growth and competitive potential. In arid regions, C 4 plants evolved safer xylem, which can increase survival and performance during drought events. 相似文献
17.
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
18.
Lower respiratory costs were hypothesized as providing an additional benefit in C 4 plants compared to C 3 plants due to less investment in proteins in C 4 leaves. Therefore, photosynthesis and dark respiration of mature leaves were compared between a number of C 4 and C 3 species. Although photosynthetic rates were generally greater in C 4 when compared to C 3 species, no differences were found in dark respiration rates of individual leaves at either the beginning or after 16 h of the dark period. The effects of nitrogen on photosynthesis and respiration of individual leaves and whole plants were also investigated in two species that occupy similar habitats, Amaranthus retroflexus (C 4) and Chenopodium album (C 3). For mature leaves of both species, there was no relationship between leaf nitrogen and leaf respiration, with leaves of both species exhibiting a similar rate of decline after 16 h of darkness. In contrast, leaf photosynthesis increased with increasing leaf nitrogen in both species, with the C 4 species displaying a greater photosynthetic response to leaf nitrogen. For whole plants of both species grown at different nitrogen levels, there was a clear linear relationship between net CO 2 uptake and CO 2 efflux in the dark. The dependence of nightly CO 2 efflux on CO 2 uptake was similar for both species, although the response of CO 2 uptake to leaf nitrogen was much steeper in the C 4 species, Amaranthus retroflexus. Rates of growth and maintenance respiration by whole plants of both species were similar, with both species displaying higher rates at higher leaf nitrogen. There were no significant differences in leaf or whole plant maintenance respiration between species at any temperature between 18 and 42°C. The data suggest no obvious differences in respiratory costs in C 4 and C 3 plants. 相似文献
19.
Photosynthetic pathway types (C 3 and C 4 species) and their dynamics along grazing gradient were determined for 42 plant species in 30 genera and 13 families from the Songnen grassland, Northeastern China. Of the total, 10 species in 9 genera and 4 families had C 4 photosynthesis; 32 species in 21 genera and 12 families had C 3 photosynthesis. The proportion of C 4 species in total plants and C 4/C 3 increased with grazing intensity, and peaked in overgrazed plot. Most of the increased C 4 species (6 of 10) along the grazed gradient were annual grasses and halophytes. This indicated that the C 4 species had greater capacity to tolerate environmental stresses ( e.g. drought and saline) caused by animal grazing in the Songnen grassland, Northeastern China. 相似文献
20.
In this report, the effects of light on the activity and allosteric properties of phospho enolpyruvate (PEP) carboxylase were examined in newly matured leaves of several C 3 and C 4 species. Illumination of previously darkened leaves increased the enzyme activity 1.1 to 1.3 fold in C 3 species and 1.4 to 2.3 fold in C 4 species, when assayed under suboptimal conditions (pH 7) without allosteric effectors. The sensitivities of PEP carboxylase to the allosteric effectors malate and glucose-6-phosphate were markedly different between C 3 and C 4 species. In the presence of 5 mM malate, the activity of the enzyme extracted from illuminated leaves was 3 to 10 fold higher than that from darkened leaves in C 4 species due to reduced malate inhibition of the enzyme from illuminated leaves, whereas it increased only slightly in C 3 species. The Ki(malate) for the enzyme increased about 3 fold by illumination in C 4 species, but increased only slightly in C 3 species. Also, the addition of the positive effector glucose-6-phosphate provided much greater protection against malate inhibition of the enzyme from C 4 species than C 3 species. Feeding nitrate to excised leaves of nitrogen deficient plants enhanced the degree of light activation of PEP carboxylase in the C 4 species maize, but had little or no effect in the C 3 species wheat. These results suggest that post-translational modification by light affects the activity and allosteric properties of PEP carboxylase to a much greater extend in C 4 than in C 3 species. 相似文献
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