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1.
The amphibious leafless sedge Eleocharis retroflexa ssp. chaetaria expresses C4-like biochemical characteristics in both the terrestrial and submerged forms. Culms of the terrestrial form have Kranz anatomy, whereas those of the submerged form have Kranz-like anatomy combined with anatomical features of aquatic plant leaves. We examined the immunolocalization of C3 and C4 enzymes in culms of the two forms. In both forms, phosphoenolpyruvate carboxylase; pyruvate, Pi dikinase; and NAD-malic enzyme were compartmentalized between the mesophyll (M) and Kranz cells, but their levels were somewhat reduced in the submerged form. In the terrestrial form, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) occurred mainly in the Kranz cells, and weakly in the M chloroplasts. In the submerged form, the rubisco occurred at higher levels in the M cells than in the terrestrial form. In both forms, the C4 pattern of enzyme expression was clearer in the M cells adjacent to Kranz cells than in distant M cells. During the transition from terrestrial to submerged conditions, the enzyme expression pattern changed in submerged mature culms that had been formed in air before submergence, and matched that in culms newly developed underwater. It seems that effects of both environmental and developmental factors overlap in the C4 pattern expression in this plant. 相似文献
2.
Photosynthetic pathways (e.g. C3, C4) and morphological functional types (e.g. trees, shrubs, high perennial grasses, perennial forbs) were identified for the native species from the Saskatchewan mixed
prairie, using the data from references published between 1950 and 2003. Of the total 219 identified species in 145 genera
and 45 families, 208 species in 137 genera and 44 families were found with C3 photosynthesis, and most of these species are dominants (e.g. Agropyron dasystachyum Hook. and Stipa spartea var. curtiseta Hitchc.). 11 species in 10 genera and 3 families were identified with C4 photosynthesis (e.g. Atriplex argentea Nutt., Andropogon scoparius Michx., Boutelou gracilis Lag., Calamovilfa longifolia Hook.). The amount of total identified C4 species in the region is much less than that from the South Dakota mixed prairie (27 species). Gramineae is the leading family with C4 photosynthesis (8 species), Chenopodiaceae ranks the second (2 species). Relatively less forb types [50 % perennial forbs (PEF) and 12 % annual forbs (ANF)] and more
graminoid types (25 %) composition suggested that the rangelands in the region are relatively stable. Lacking of the knowledge
on the optimal traits for PFTs classification in the region, further studies (e.g. C3 and C4 plant identification and optimal trait selection) are needed to explore the relationships between PFTs and vegetation variations,
as well as land-use and climate changes. 相似文献
3.
The increasing CO2 concentration in Earths atmosphere is expected to cause a greater decline in the nutritional quality of C3 than C4 plants. As a compensatory response, herbivorous insects may increase their feeding disproportionately on C3 plants. These hypotheses were tested by growing the grasses Lolium multiflorum C3) and Bouteloua curtipendula C4) at ambient (370 ppm) and elevated (740 ppm) CO2 levels in open top chambers in the field, and comparing the growth and digestive efficiencies of the generalist grasshopper Melanoplus sanguinipes on each of the four plant × CO2 treatment combinations. As expected, the nutritional quality of the C3 grass declined to a greater extent than did that of the C4 grass at elevated CO2; protein levels declined in the C3 grass, while levels of carbohydrates (sugar, fructan and starch) increased. However, M. sanguinipes did not significantly increase its consumption rate to compensate for the lower nutritional quality of the C3 grass grown under elevated CO2. Instead, these grasshoppers appear to use post-ingestive mechanisms to maintain their growth rates on the C3 grass under elevated CO2. Consumption rates of the C3 and C4 grasses were also similar, demonstrating a lack of compensatory feeding on the C4 grass. We also examined the relative efficiencies of nutrient utilization from a C3 and C4 grass by M. sanguinipes to test the basis for the C4 plant avoidance hypothesis. Contrary to this hypothesis, neither protein nor sugar was digested with a lower efficiency from the C4 grass than from the C3 grass. A novel finding of this study is that fructan, a potentially large carbohydrate source in C3 grasses, is utilized by grasshoppers. Based on the higher nutrient levels in the C3 grass and the better growth performance of M. sanguinipes on this grass at both CO2 levels, we conclude that C3 grasses are likely to remain better host plants than C4 grasses in future CO2 conditions. 相似文献
4.
We describe the long-term effects of a CO2 exhalation, created more than 70 years ago, on a natural C4 dominated sub-tropical grassland in terms of ecosystem structure and functioning. We tested whether long-term CO2 enrichment changes the competitive balance between plants with C3 and C4 photosynthetic pathways and how CO2 enrichment has affected species composition, plant growth responses, leaf properties and soil nutrient, carbon and water dynamics. Long-term effects of elevated CO2 on plant community composition and system processes in this sub-tropical grassland indicate very subtle changes in ecosystem functioning and no changes in species composition and dominance which could be ascribed to elevated CO2 alone. Species compositional data and soil δ13C isotopic evidence suggest no detectable effect of CO2 enrichment on C3:C4 plant mixtures and individual species dominance. Contrary to many general predictions C3 grasses did not become more abundant and C3 shrubs and trees did not invade the site. No season length stimulation of plant growth was found even after 5 years of exposure to CO2 concentrations averaging 610 μmol mol−1. Leaf properties such as total N decreased in the C3 but not C4 grass under elevated CO2 while total non-structural carbohydrate accumulation was not affected. Elevated CO2 possibly lead to increased end-of-season soil water contents and this result agrees with earlier studies despite the topographic water gradient being a confounding problem at our research site. Long-term CO2 enrichment also had little effect on soil carbon storage with no detectable changes in soil organic matter found. There were indications that potential soil respiration and N mineralization rates could be higher in soils close to the CO2 source. The conservative response of this grassland suggests that many of the reported effects of elevated CO2 on similar ecosystems could be short duration experimental artefacts that disappear under long-term elevated CO2 conditions. 相似文献
5.
Sulfate assimilation and glutathione synthesis were traditionally believed to be differentially compartmentalised in C4 plants with the synthesis of cysteine and glutathione restricted to bundle sheath and mesophyll cells, respectively. Recent
studies, however, showed that although ATP sulfurylase and adenosine 5′ phosphosulfate reductase, the key enzymes of sulfate
assimilation, are localised exclusively in bundle sheath in maize and other C4 monocot species, this is not true for the dicot C4 species of Flaveria. On the other hand, enzymes of glutathione biosynthesis were demonstrated to be active in both types of maize cells. Therefore,
in this review the recent findings on compartmentation of sulfate assimilation and glutathione metabolism in C4 plants will be summarised and the consequences for our understanding of sulfate metabolism and C4 photosynthesis will be discussed. 相似文献
6.
Spatial patterns of foliar stable carbon isotope compositions of C<Subscript>3</Subscript> plant species in the Loess Plateau of China 总被引:1,自引:0,他引:1
The spatial pattern of foliar stable carbon isotope compositions (δ13C) of dominant species and their relationships with environmental factors in seven sites, Yangling, Yongshou, Tongchuan, Fuxian,
Ansai, Mizhi and Shenmu, standing from south to north in the Loess Plateau of China, was studied. The results showed that
in the 121 C3 plant samples collected from the Loess Plateau, the foliar δ13C value ranged from −22.66‰ to −30.70‰, averaging −27.04‰. The foliar δ13C value varied significantly (P<0.01) among the seven sites, and the average δ13C value increased by about 1.69‰ from Yangling in the south to Shenmu in the north as climatic drought increased. There was
a significant difference in foliar δ13C value among three life-forms categorized from all the plant samples in the Loess Plateau (P<0.001). The trees (−26.74‰) and shrubs (−26.68‰) had similar mean δ13C values, both significantly (P<0.05) higher than the mean δ13C value of herbages (−27.69‰). It was shown that the trees and shrubs had higher WUEs and employed more conservative water-use
patterns to survive drier habitats in the Loess Plateau. Of all the C3 species in the Loess Plateau, the foliar δ13C values were significantly and negatively correlated with the mean annual rainfall (P<0.001) and mean annual temperature (P<0.05), while being significantly and positively correlated with the latitude (P<0.001) and the annual solar radiation (P<0.01). In general, the foliar δ13C values increased as the latitude and solar radiation increased and the rainfall and temperature decreased. The annual rainfall
as the main influencing factor could explain 13.3% of the spatial variations in foliar δ13C value. A 100 mm increment in annual rainfall would result in a decrease by 0.88‰ in foliar δ13C values. 相似文献
7.
The natural occurrence and altitudinal pattern of species with C4 photosynthesis were investigated on Qinghai Plateau, Qinghai province by using stable carbon isotopes in plant leaves and
using additional data from references. A total of 58 species belonging to 10 families and 34 genera were identified using
C4 photosynthetic pathway, which is only 1.66 % of total 3 500 plant species in Qinghai province. The leading two families,
i.e. Gramineae (23 species) and Chenopodiaceae (22 species) contain 77.6 % of all C4 plants in the studied area. The number of C4 species increased from 1 600 to 2 400 m a.s.l. and then decreases quickly till 4 400 m a.s.l. with one half of C4 species distributing from 2 200 to 2 800 m a.s.l. (48 %). Eight plant species were found above 4 000 m a.s.l., but the distribution
of these species is limited to the south of Qinghai province (low latitude area) where annual mean temperature is above 0
°C, suggesting that low temperature may generally limit the distribution of C4 plants. 相似文献
8.
Hydrogen peroxide (H2O2) as a source of reactive oxygen species (ROS) significantly stimulated germination of switchgrass (Panicum virgatum L.) seeds with an optimal concentration of 20 mM at both 25 and 35°C. For non-dormant switchgrass seeds exhibiting different
levels of germination, treatment with H2O2 resulted in rapid germination (<3 days) of all germinable seeds as compared to seeds placed on water. Exposure to 20 mM H2O2 elicited simultaneous growth of the root and shoot system, resulting in more uniform seedling development. Seeds of big bluestem
(Andropogon gerardii Vitman) and indiangrass [Sorghastrum nutans (L.) Nash] also responded positively to H2O2 treatment, indicating the universality of the effect of H2O2 on seed germination in warm-season prairie grasses. For switchgrass seeds, abscisic acid (ABA) and the NADPH-oxidase inhibitor,
diphenyleneiodonium (DPI) at 20 μM retarded germination (radicle emergence), stunted root growth and partially inhibited NADPH-oxidase
activity in seeds. H2O2 reversed the inhibitory effects of DPI and ABA on germination and coleoptile elongation, but did not overcome DPI inhibition
of root elongation. Treatment with H2O2 appeared to enhance endogenous production of nitric oxide, and a scavenger of nitric oxide abolished the peroxide-responsive
stimulation of switchgrass seed germination. The activities and levels of several proteins changed earlier in seeds imbibed
on H2O2 as compared to seeds maintained on water or on ABA. These data demonstrate that seed germination of warm-season grasses is
significantly responsive to oxidative conditions and highlights the complex interplay between seed redox status, ABA, ROS
and NO in this system. 相似文献
9.
We combined measurements of short-term (during gas exchange) and long-term (from plant dry matter) carbon isotope discrimination
to estimate CO2 leakiness from bundle sheath cells in six C4 species (three grasses and three dicots) as a function of leaf insertion level, growth temperature and short-term irradiance.
The two methods for determining leakiness yielded similar results (P > 0.05) for all species except Setaria macrostachya, which may be explained by the leaf of this species not being accommodating to gas exchange. Leaf insertion level had no
effect on leakiness. At the highest growth temperature (36°C) leakiness was lower than at the two lower growth temperatures
(16°C and 26°C), between which no differences in leakiness were apparent. Higher irradiance decreased leakiness in three species,
while it had no significant effect on the others (there was an opposite trend in two species). The inverse response to increasing
irradiance was most marked in the two NAD-ME dicots (both Amaranthus species), which both showed almost 50% leakiness at low light (300 μmol quanta m−2 s−1) compared to about 30% at high light (1,600 μmol quanta m−2 s−1). NADP-ME subtype grasses had lower leakiness than NAD-ME dicots. Although there were exceptions, particularly in the effect
of irradiance on leakiness in Sorghum and Boerhavia, we conclude that conditions favourable to C4 photosynthesis (high temperature and high light) lead to a reduction in leakiness. 相似文献
10.
Plant functional types and their ecological responses to salinization in saline grasslands, Northeastern China 总被引:3,自引:0,他引:3
R.Z. Wang 《Photosynthetica》2004,42(4):511-519
Photosynthetic pathways (C3, C4, and CAM) and morphological functional types (e.g. shrubs, high perennial grasses, short perennial graminaceous plants, annual grasses, annual forbs, perennial forbs, halophytes, and hydrophytes) were identified for the species from salinity grasslands in Northeastern China, using the data from both stable carbon isotope ratios (13C) and from the references published between 1993 and 2002. 150 species, in 99 genera and 37 families, were found with C3 photosynthesis, and most of these species are dominants [e.g. Leymus chinensis (Trin.) Tzvel., Calamagrostis epigeios (L.), Suaeda corniculata (C.A. Mey.) Bunge]. 40 species in 25 genera and 8 families were identified with C4 photosynthesis [e.g. Chloris virgata Sw., Aeluropus littoralis (Gouan) Parlat] and 1 species with CAM photosynthesis. Gramineae is the leading family with C4 photosynthesis (27 species), Chenopodiaceae ranks the second (5 species). The significant increase of C4 proportions with intense salinity suggested this type plant is remarkable response to the grassland salinization in the region. 191 species were classified into eight morphological functional types and the changes of most of these types (e.g. PEF, HAL, and HPG) were consistent with habitats and vegetation dynamics in the saline grassland. My findings suggest that the photosynthetic pathways, combined with morphological functional types, are efficient means for studying the linkage between species and ecosystems in this type of saline grassland in Northeastern China.This revised version was published online in March 2005 with corrections to the page numbers. 相似文献
11.
In C4 plants, photorespiration is decreased relative to C3 plants. However, it remains unclear how much photorespiratory capacity C4 leaf tissues actually have. We thoroughly investigated the quantitative distribution of photorespiratory organelles and the immunogold localization of the P protein of glycine decarboxylase (GDC) in mesophyll (M) and bundle sheath (BS) cells of various C4 grass species. Specific differences occurred in the proportions of mitochondria and peroxisomes in the BS cells (relative to the M cells) in photosynthetic tissues surrounding a vein: lower in the NADP-malic enzyme (NADP-ME) species having poorly formed grana in the BS chloroplasts, and higher in the NAD-malic enzyme (NAD-ME) and phosphoenolpyruvate carboxykinase (PCK) species having well developed grana. In all C4 species, GDC was localized mainly in the BS mitochondria. When the total amounts of GDC in the BS mitochondria per unit leaf width were estimated from the immunogold labeling density and the quantity of mitochondria, the BSs of NADP-ME species contained less GDC than those of NAD-ME or PCK species. This trend was also verified by immunoblot analysis of leaf soluble protein. There was a high positive correlation between the degree of granal development (granal index) in the BS chloroplasts and the total amount of GDC in the BS mitochondria. The variations in the structural and biochemical features involved in photorespiration found among C4 species might reflect differences in the O2/CO2 partial pressure and in the potential photorespiratory capacity of the BS cells.Abbreviations BS Bundle sheath - GDC Glycine decarboxylase - M Mesophyll - NAD-ME NAD-malic enzyme - NADP-ME NADP-malic enzyme - PCK Phosphoenolpyruvate carboxykinase 相似文献
12.
A controlled environment experiment was conducted to determine the impact of enhanced carbon dioxide and temperature on competition between the C3 grasses Austrodanthonia eriantha and Vulpia myuros. Plants were grown in mixtures and monocultures to compare the responses both with and without an interspecific competitor. Temperature and CO2 were set at current levels (350 ppm CO2; 20 °C day and 10 °C night temperature), in factorial combination with enhanced levels (700 ppm CO2; 23 °C day and 13 °C night temperature). To examine the potential impact of initial seedling size on competition under elevated CO2 and temperature, the two species were combined in mixtures of differing initial sizes. Above-ground growth of all plants was enhanced by increased CO2 and temperature alone, however the combined temperature and CO2 treatment showed a sub-additive effect, where growth was less than expected based on the responses to each factor independently. Austrodanthonia in mixture with Vulpia plants of the same initial size experienced a 27 reduction in growth. Austrodanthonia grown in the presence of an initially larger Vulpia plant experienced a 58 reduction in growth. When the Vulpia plant was initially smaller than Austrodanthonia, growth of the Austrodanthonia was reduced by 16%. The growth of Vulpia appeared to be largely unaffected by the presence of Austrodanthonia. Variation in the CO2 and temperature environment did not affect the pattern of these interspecific interactions, although there was some evidence to suggest that the degree of suppression of Austrodanthonia by Vulpia was less under elevated CO2. These results do not support the initial advantage hypothesis, as Vulpia was always able to suppress Austrodanthonia, regardless of the initial relative sizes of the competitors. Furthermore, the lack of an effect of changing the CO2 or temperature environment on the direction of interspecific competition suggests that the competitiveness of the invasive Vulpia will be minimally affected by changes in atmospheric CO2 concentration or temperature. 相似文献
13.
The potential for C4 photosynthesis was investigated in five C3-C4 intermediate species, one C3 species, and one C4 species in the genus Flaveria, using 14CO2 pulse-12CO2 chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating 14CO2 into the C4 acids malate and aspartate, following an 8-s pulse. The proportion of 14C label in these C4 products ranged from 50–55% to 20–26% in the C3-C4 intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, 14CO2 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 C4 photosynthesis among the intermediate species based on the apparent rate of conversion of 14C label from the C4 cycle to the C3 cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C4-cycle products and an increase in percentage label in C3-cycle products during chase periods with 12CO2, although the rate of change was slower than in the C4 species, F. palmeri. In these C3-C4 intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C3-C4 intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C4-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 C4 and C3 cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C3 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 C4-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O2, the absorbed quantum yields for CO2 uptake (in mol CO2·[mol quanta]-1) averaged 0.053 in F. cronquistii (C3), 0.051 in F. trinervia (Spreng.) Mohr (C4), 0.052 in F. ramosissima (C3-C4), 0.051 in F. anomala (C3-C4), 0.050 in F. linearis (C3-C4), 0.046 in F. floridana (C3-C4), and 0.044 in F. pubescens (C3-C4). In 2% O2 an enhancement of the quantum yield was observed in all of the C3-C4 intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O2 were intermediate in value to the C3 and C4 species, indicating a co-function of the C3 and C4 cycles in CO2 assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O2 presumably reflect an ineffcient transfer of carbon from the C4 to the C3 cycle. The response of the quantum yield to four increasing O2 concentrations (2–35%) showed lower levels of O2 inhibition in the C3-C4 intermediate F. ramosissima, relative to the C3 species. This indicates that the co-function of the C3 and C4 cycles in this intermediate species leads to an increased CO2 concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O2.Abbreviations PEP
phosphoenolpyruvate
- PGA
3-phosphoglycerate
- RuBP
ribulose-1,5-bisphosphate 相似文献
14.
Ogle K 《Oecologia》2003,136(4):532-542
The distance between veins has the potential to affect photosynthesis in C4 grasses because photon capture and photosynthetic carbon reduction are primarily restricted to vascular bundle sheath cells (BSC). For example, BSC density should increase as interveinal distance (IVD) decreases, and thus IVD may influence photon capture and photosynthesis in C4 grasses. The objective of this study is to evaluate the potential importance of IVD to the function of C4 grasses, and a literature survey is conducted to test the hypothesis that quantum yield of photosynthesis () increases with decreasing IVD. First, a meta-analysis of and IVD values obtained for 12 C4 grass species supports this hypothesis as and IVD are significantly negatively correlated (r=–0.61). Second, a regression of carbon isotope discrimination () versus IVD was conducted and the regression equation was used in a simple biochemical model that relates to and leakage of CO2 from the BSC. The modeling analysis also supports the hypothesis that decreases with increasing IVD in C4 grasses. C4 grasses are virtually absent from shaded habitats, and the biochemical model is employed to examine the implications of IVD for shade-tolerance in C4 grasses. The model predicts that only those species with uncommonly small IVD values are able to tolerate prolonged shade. 相似文献
15.
C4 plants are rare in cool climates, an ecological pattern attributable to their poor photosynthetic performance at low temperatures relative to C3 species. However, some C4 species are able to persist at high latitudes and high elevations, possibly due to the characteristics of the particular microsites they inhabit in these otherwise unfavourable environments. One such species is Muhlenbergia glomerata, which occurs above 60°N in Canada and is found in the atypical C4 habitat of boreal fens. In this study, we evaluate how microsite features affect the success of M. glomerata in boreal fens. We surveyed 19 populations across northern Ontario during the summers of 1999 and 2000. The ground coverage by woody vegetation was the most important parameter affecting the presence or absence of M. glomerata. Woody plants covered over 50% of the ground area in plots where M. glomerata is absent, but less than 20% where it is present. The minimum light intensity threshold for the presence of the C4 species was about 32% of full-sunlight at plant height. Surprisingly, in boreal fens M. glomerata was largely restricted to the wetter moss hollows, rather than occurring on the dry hummocks where its greater water use efficiency might have been advantageous. Woody species dominated the hummocks, but were uncommon in the hollows. In these cool northern climates M. glomerata apparently persists because sufficient periods of temperatures favourable to C4 photosynthesis occur, but this persistence likely requires some factor that suppresses the woody vegetation. 相似文献
16.
Photosynthetic pathway Types (C3, C4, and CAM) and life forms of native species from Hulunbeier rangelands, north China were studied. Of the total 258 species, 216 species in 132 genera and 42 families had C3 photosynthetic pathway, including dominant herbs, e.g. Stipa baicalensis Roshev. and Leymus chinensis (Trin.) Tzvel., Filifolium sibiricum Kitam. and Arudinella hirta (Thunb.) Koidz. 38 species in 28 genera and 10 families were found with C4 photosynthesis, and 4 species in 2 genera and 1 family had CAM photosynthetic pathway. The occurrence of C4 species was common in Gramineae and Chenopodiaceae, and the two families were leading ones within C4 plants. More than 52 % of the total 258 species were in H form, 21 % in Th form, 19 % in G form; the other life form Types, e.g. Ch, M, N, and HH, formed less than 3 %. 68 % of C4 species were in Th form and 24 % in H form, indicating that these Types were the dominant life forms for C4 species in the rangeland region. The occurrence of C4 species was closely related with plant habitats, disturbed lands had the highest C4 abundance (55 % of the total C4 species), followed by grasslands and sandy soil, and forests had the lowest C4 abundance (8 %). Hence the occurrence of C4 species could be efficient indicator for rangeland dynamics in Hulunbeier rangelands. 相似文献
17.
D. A. Aliverdieva D. V. Mamaev 《Journal of Evolutionary Biochemistry and Physiology》2009,45(3):323-339
An important role in cell metabolism is played by transport of C4-dicarboxylates (C4-DCB). Specifically, they are intermediates of the citrate cycle. Transport of succinate across the mitochondrial membrane provides correlation between metabolism in peroxysomes and in mitochondria. There is known transport of C4-DCB across all kinds of energy-transforming membranes of the animal, plant, fungal, and bacterial cells. This review summarizes molecular characteristics of the C4-DCB transporters. Of particular interest are primary structures for the transporters with the known kinetic mechanism and kinetic transport parameters. For each studied group of organisms, the number of transmembrane segments in the carried molecule or the character of specificity does not correlate with the certain transport mechanism—antiport, symport with proton or symport with cation. The review describes perspective methodical approaches allowing association of peculiarities of structure with transport mechanism for individual transporters, preparation of functional hybrid transporters—“protein chimeras,” scanning of transporter transmembrane segments with aid of essential acids, probing of the transporter active center with aid of alkyl and acyl substrate derivatives used to obtain the “lipophilic profile” of the channel of the C4-DCB transporter. It is recommended to use these approaches to one transporter that has small sizes and large substrate specificity. 相似文献
18.
Clusia minor L. is a C3-CAM species in which Crassulacean acid Metabolism (CAM) is induced, among other factors, by water deficit. We propose that
CAM induction by natural drought in C. minor shifts the sap flow pattern from daytime to a night-time one, and that the decreased osmotic potential due to increased malate
content in droughted plants aids in the increase in nocturnal sap flow. In order to test these hypotheses, we followed for
2 years the seasonal changes in parameters of water relationships and sap flow velocity in one single, freestanding tree growing
in Caracas. Leaf water and osmotic potential were measured psychrometrically, nocturnal proton accumulation by titration of
aqueous leaf extracts and sap flow density with thermal dissipation probes. Leaf water, osmotic and turgor potential remained
relatively high throughout the seasons. Nocturnal proton accumulation was nil under extreme drought or after frequent and
heavy rains, and high after moderate rainfall. Estimated malate and citrate concentrations contributed up to 80 and 60%, respectively,
of the value of osmotic potential. The shape of the daily courses of sap flow velocity varied seasonally, from mostly diurnal
during the dry season to mostly nocturnal after a short dry spell during the rainy season, when nocturnal acid accumulation
attained high values. There was a strong positive relationship between the proportion of the integrated sap flow courses corresponding
to the night and dawn [H+] (r
2 = 0.88). Increased nocturnal sap flow in the CAM stage of the tree of C. minor may be explained by a lower osmotic potential due to an increased acid concentration, together with increased stomatal aperture,
as suggested by increased nocturnal acid accumulation probably due to nocturnal CO2 fixation. 相似文献
19.
Photosynthetic Pathway Types of Forage Species Along Grazing Gradient from the Songnen Grassland,Northeastern China 总被引:3,自引:0,他引:3
Photosynthetic pathway types (C3 and C4 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 C4 photosynthesis; 32 species in 21 genera and 12 families had C3 photosynthesis. The proportion of C4 species in total plants and C4/C3 increased with grazing intensity, and peaked in overgrazed plot. Most of the increased C4 species (6 of 10) along the grazed gradient were annual grasses and halophytes. This indicated that the C4 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.
Photosynthetic and morphological functional types from different steppe communities in Inner Mongolia, North China 总被引:1,自引:0,他引:1
R. Z. Wang 《Photosynthetica》2004,42(4):493-503
Morphological functional types and photosynthetic pathway types were identified for the forage species from steppe communities in Inner Mongolia, China, using the data of both field survey and published papers. Seven typical steppe communities were selected to investigate the morphological functional type and photosynthetic pathway type compositions and plant functional type (PFT) diversity in steppe communities at regional scale. Morphological functional types, based on plant height and leaf type combined with life span, were optimal for comparing the community differences in the region, while photosynthetic pathway types were fairly coarse for such studies. Of the seven morphological functional types in the steppe communities, perennial forbs (PEF) were the dominant type, and 60 % of species belonged to this type. Each of the high perennial grass (HPG), short perennial grass (SPG), and annual grass (ANG) types represented less than 10 % of the total, even though the grass species were dominant in the seven steppe communities. The differences of PFTs between the steppe communities were remarkable, and the PFT richness and diversity increased from the communities with moist conditions to the ones with dry environments.This revised version was published online in March 2005 with corrections to the page numbers. 相似文献