Plio-Pleistocene vegetation changes in the North China Plain: Magnetostratigraphy, oxygen and carbon isotopic composition of pedogenic carbonates

The Plio-Pleistocene history of C₄ plant biomass in northwestern China has been documented from the loess-soil sequences of the Loess Plateau region. However, how C₄ plants evolved in the warmer and low-elevation eastern China monsoon zone is still poorly known mainly because of the unavailability of well-dated geological records. In this study, a 203.6-m core of floodplain deposits was recovered from the North China Plain near Tianjin and dated magnetostratigraphically. The results define a chronosequence for the last 3.3 Ma. The late Quaternary portion of the core consists of fluvio-marine sediments while the rest of the section (3.3-0.6 Ma) contains abundant paleosols formed on the floodplain, as confirmed by soil micromorphological evidence. The stable carbon and oxygen isotopic composition of pedogenic carbonates was measured to document vegetation and climate changes. The results reveal mixed C₃ and C₄ vegetation with an estimated C₄ abundance of ~ 40-60% from ~ 3.1 to ~ 2.2 Ma, and a subsequent gradual decline to ~ 25% until ~ 0.6 Ma. This trend is consistent with the data from the loess-soil sequences further west on the Loess Plateau, suggesting they are regionally significant changes. The lowering of growing-season temperature and/or drier conditions induced by global cooling would explain this overall decline.     

The carbon isotope ecology and diet of Australopithecus africanus at Sterkfontein,South Africa

The stable carbon isotope ratio of fossil tooth enamel carbonate is determined by the photosynthetic systems of plants at the base of the animal's foodweb. In subtropical Africa, grasses and many sedges have C(4)photosynthesis and transmit their characteristically enriched 13C/(12)C ratios (more positive delta13C values) along the foodchain to consumers. We report here a carbon isotope study of ten specimens of Australopithecus africanus from Member 4, Sterkfontein (ca. 2.5 to 2.0Ma), compared with other fossil mammals from the same deposit. This is the most extensive isotopic study of an early hominin species that has been achieved so far. The results show that this hominin was intensively engaged with the savanna foodweb and that the dietary variation between individuals was more pronounced than for any other early hominin or non-human primate species on record. Suggestions that more than one species have been incuded in this taxon are not supported by the isotopic evidence. We conclude that Australopithecus africanus was highly opportunistic and adaptable in its feeding habits.     

Leaf gas exchange characteristics and water- and nitrogen-use efficiencies of dominant grass and tree species in a West African savanna

Whereas leaf gas exchange properties are important to assess carbon and water fluxes in ecosystems worldwide, information of this type is scarce for savanna species. In this study, gas exchange characteristics of 2 C₄ grass species (Andropogon canaliculatus and Hyparrhenia diplandra) and 2 C₃ tree species (Crossopteryx febrifuga and Cussonia arborea) from the West-African savanna of Lamto (Ivory Coast) were investigated in the field. Measurements were done in order to provide data to allow the parameterization of biochemically-based models of photosynthesis (for C₄ and C₃ plant metabolic types) and stomatal conductance ; and to compare gas exchange characteristics of coexisting species. No systematic difference was found between grass and tree species for reference stomatal conductance, under standard environmental conditions, or stomatal response to incident light or vapour pressure deficit at leaf surface. Conversely, grass species displayed higher water (1.5-2 fold) and nitrogen (2-5 fold) photosynthetic use efficiencies (WUE and NUE, ratio of net photosynthesis to transpiration and leaf nitrogen, respectively). These contrasts were attributed to the CO₂ concentrating mechanism of C₄ plants. When looking within plant life forms, no important difference was found between grass species. However, significant contrasts were found between tree species, Cussonia showing higher NUE and reference stomatal conductance than Crossopteryx. These results stress the need to account for functional diversity when estimating ecosystem carbon and water fluxes. In particular, our results suggest that the tree/grass ratio, and also the composition of the tree layer, could strongly affect WUE and NUE at the ecosystem scale in West African savannas.     

Long-term effects of elevated atmospheric CO<Subscript>2</Subscript> on species composition and productivity of a southern African C<Subscript>4</Subscript> dominated grassland in the vicinity of a CO<Subscript>2</Subscript> exhalation

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.     

Light and growth temperature alter carbon isotope discrimination and estimated bundle sheath leakiness in C<Subscript>4</Subscript> grasses and dicots

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.     

Carbon fixation and carbonic anhydrase activity in Haslea ostrearia (Bacillariophyceae) in relation to growth irradiance

The metabolic pathway of primary carbon fixation was studied in a peculiar pennate marine diatom, Haslea ostrearia (Bory) Simonsen, which synthesizes and accumulates a blue pigment known as “marennine”. Cells were cultured in a semi-continuous mode under saturating [350 μmol(photon) m⁻² s⁻¹] or non-saturating [25 μmol(photon) m⁻² s⁻¹] irradiance producing “blue” (BC) and “green” (GC) cells, characterized by high and low marennine accumulation, respectively. Growth, pigment contents (chlorophyll a and marennine), ¹⁴C accumulation in the metabolites, and the carbonic anhydrase (CA) activity of the cells were determined during the exponential growth phase. Growth rate and marennine content were closely linked to irradiance during growth: higher irradiance increased both growth rate and marennine content. On the other hand, the Chl a concentration was lower under saturating irradiance. The distribution between the Calvin-Benson (C₃) and β-carboxylation (C₄) pathways was very different depending on the irradiance during growth. Metabolites of the C₃ cycle contained about 70 % of the total fixed radioactivity after 60 s of incorporation into cells cultured under the non-saturating irradiance (GC), but only 47 % under saturating irradiance (BC). At the same time, carbon fixation by β-carboxylation was 24 % in GC versus about 41 % in BC, becoming equal to that in the C₃ fixation pathway in the latter. Internal CA activity remained constant, but the periplasmic CA activity was higher under low than high irradiance.     

Winter-spring precipitation as the principal control on predominance of C3 plants in Central Asia over the past 1.77 Myr: Evidence from δC of loess organic matter in Tajikistan

Although changes in atmospheric CO₂ levels are thought to be the major factor driving long-term C₃/C₄ vegetation evolution, recent studies tend to emphasize the effect of regional climate conditions on C₃/C₄ variations. The middle latitudes (30-45°), in which C₃/C₄ plants are highly sensitive to environmental changes, provide an optimal basis for the investigation of the relative impacts of climate and pCO₂ on shifts in C₃/C₄ cover. In order to assess the factors controlling these shifts as well as the complex interactions between environmental factors, the carbon isotopic composition of bulk organic matter from the Chashmanigar loess section (southern Tajikistan) was measured for the past 1.77 Myr. In general, the δ¹³C record shows mostly negative values throughout the sequence, almost all δ¹³C values falling between − 23‰ and − 26‰, indicating a predominance of C₃ plants in Central Asia over this time period, despite the presence of numerous glacial-interglacial cycles. From 0.85 Myr to the present, the δ¹³C values become increasingly positive, reflecting a growing C₄ signal. However, this C₄ component is not detectable prior to 0.25 Myr, after which minor peaks are evident at ∼ 228, ∼ 171 and ∼ 18 kyr. The δ¹³C record from Chashmanigar indicates that winter-spring precipitation, i.e., Mediterranean climatic conditions, have characterized Central Asia throughout the past 1.77 Myr, leading to the predominance of C₃ vegetation. In the context of glacial-interglacial-scale changes in atmospheric CO₂, therefore, it is climate rather than pCO₂ that controls C₃/C₄ variations in Asia’s middle latitudes. The gradual increase in the C₄ component since 0.85 Myr, especially the notable peaks after 0.25 Myr, may have been caused by an increase in summer precipitation due to an enhanced southward shift of the climate zones.     

Diversity in forms of C4 in the genus Cleome (Cleomaceae)

Background and Aims

Cleomaceae is one of 19 angiosperm families in which C₄ photosynthesis has been reported. The aim of the study was to determine the type, and diversity, of structural and functional forms of C₄ in genus Cleome.

Methods

Plants 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 Results

Three species with C₄-type carbon isotope values occurring in separate lineages in the genus (Cleome angustifolia, C. gynandra and C. oxalidea) were shown to have features of C₄ 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 C₄ cycle (compared with the C₃–C₄ intermediate C. paradoxa and the C₃ 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.

Conclusions

NAD-malic enzyme-type C₄ 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, C₃–C₄ intermediate African species C. paradoxa, suggests adaptation of this lineage to arid environments, which is supported by biogeographical information.     

Acquisition and assimilation of gaseous ammonia as revealed by intracellular pH changes in leaves of higher plants

Atmospheric ammonia (NH₃) from various anthropogenic sources has become a serious problem for natural vegetation. Ammonia not only causes changes in plant nitrogen metabolism, but also affects the acid-base balance of plants. Using the pH-sensitive fluorescent dyes pyranine and esculin, cytosolic and vacuolar pH changes were measured in leaves of C₃ and C₄ plants exposed for brief periods to concentrations of NH₃ in air ranging from 1.33 to 8.29 mol NH₃ · mol^-1 gas (0.94–5.86 mg · m^-3). After a lag phase, uptake of NH₃ from air at a rate of 200 nmol NH₃ · m ^{- 2} leaf area · s^{- 1} into leaves of Zea mays L. increased pyranine fluorescence indicating cytosolic alkalinisation. The increase was much larger in the dark than in the light. In illuminated leaves of the C₃ plant Pelargonium zonale L. and the C₄ plants Z. mays and Amaranthus caudatus L., NH₃-dependent cytosolic alkalinisation was particularly pronounced when CO₂ was supplied at very low levels (16 or 20 mol CO₂ · mol^{- 1} gas, containing 210 mmol O₂ · mol^{- 1} gas). An increase in esculin fluorescence, which was smaller than that of pyranine, was indicative of trapping of some of the NH₃ in the vacuoles of leaves of Spinacia oleracea L. and Z. mays. Photosynthesis and transpiration remained unchanged during exposure of illuminated leaves to NH₃, yielding an influx of 200 nmol NH₃ · m^-2 leaf area · s^-1 for up to 30 min, the longest exposure time used. Both CO₂ and O₂ influenced the extent of cytosolic alkalinisation. At 500 mol CO₂ · mol^-1 gas the cytosolic alkalinisation was suppressed more than at 16 or 20 mol CO₂ · mol^-1 gas. The suppressing effect of CO₂ on the NH₃induced alkalinisation was larger in illuminated leaves of the C₄ plants Z. mays and A. caudatus than in leaves of the C₃ plant P. zonale. A reduction of the O₂ concentration from 210 to 10 mmol O₂ · mol ^-1 gas, which inhibits photorespiration, increased the NH₃induced cytosolic alkalinisation in C₃ plants. Suppression by CO₂ or O₂ of the alkaline pH shift caused by the dissolution and protonation of NH₃ in queous leaf compartments, and possibly by the production of organic compounds synthesised from atmospheric NH₃, indicates that NH₃ which enters leaves is rapidly assimilated if photosynthesis or photorespiration provide nitrogen acceptor molecules.This work was supported by the Biotechnology and Biological Sciences Research Council and the Deutsche Forschungsgemein-schaft within the framework of the research of Sonderforschun-gsbreich 251 of the University of Würzburg. We are grateful to Dr. B. Wollenweber (The Royal Veterinary and Agricultural University, Denmark) for discussions.     

Patterns of phosphoenolpyruvate carboxylase activity and cytosolic pH during light activation and dark deactivation in C3 and C4 plants

The rate and extent of light activation of PEPC may be used as another criterion to distinguish C₃ and C₄ plants. Light stimulated phosphoenolypyruvate carboxylase (PEPC) in leaf discs of C₄ plants, the activity being three times greater than that in the dark but stimulation of PEPC was limited about 30% over the dark-control in C₃ species. The light activation of PEPC in leaves of C₃ plants was complete within 10 min, while maximum activation in C₄ plants required illumination for more than 20 min, indicating that the relative pace of PEPC activation was slower in C₄ plants than in C₃ plants. Similarly, the dark-deactivation of the enzyme was also slower in leaves of C₄ than in C₃ species. The extent of PEPC stimulation in the alkaline pH range indicated that the dark-adapted form of the C₄ enzyme is very sensitive to changes in pH. The pH of cytosol-enriched cell sap extracted from illuminated leaves of C₄ plants was more alkaline than that of dark-adapted leaves. The extent of such light-dependent alkalization of cell sap was three times higher in C₄ leaves than in C₃ plants. The course of light-induced alkalization and dark-acidification of cytosol-enriched cell sap was markedly similar to the pattern of light activation and dark-deactivation of PEPC in Alternanthera pungens, a C₄ plant. Our report provides preliminary evidence that the photoactivation of PEPC in C₄ plants may be mediated at least partially by the modulation of cytosolic pH.Abbreviations CAM Crassulacean acid metabolism - G-6-P glucose-6-phosphate - PMSF phenylmethylsulfonyl fluoride - PEPC phosphoenolpyruvate carboxylase - PEPC-PK phosphoenolpyruvate ca carboxylase-protein kinase     

Light-induced pH changes in leaves of C4 plants

Light-induced changes in the fluorescence of the pH-indicating dyes pyranine or 5-(and 6-)carboxy-2, 7-dichlorofluorescein (CDCF) which had been fed to leaves were examined to monitor cellular pH changes. After short-term feeding of pyranine (pK 7.3) to leaves of Amaranthus caudatus L., a NAD-malic-enzyme-type C₄ plant, vascular bundles and surrounding cells became fluorescent. Fluorescence emission from mesophyll cells required longer feeding times. In CO₂-free air, pyranine fluorescence increased much more on illumination after mesophyll cells had become fluorescent than when only the vascular bundles and the bundle sheath of Amaranthus leaves had been stained. After short feeding times and in the absence of actinic illumination, CO₂ decreased pyranine fluorescence very slowly in Amaranthus and rapidly in C₃ leaves. After prolonged feeding times, the extent of the light-dependent increase in pyranine fluorescence was several times greater in different C₄ plants than in C₃ species. The kinetics of the fluorescence changes were also remarkably different in C₃ and C₄ plants. Carbon dioxide (500 l · l^–1) suppressed the light-induced increase in pyranine fluorescence more in C₄ than in C₃ leaves. Light-dependent changes in light scattering, which are indicative of chloroplast energization, and in 410-nm transmission, which indicate chloroplast movement, differed kinetically from those of the changes in pyranine fluorescence. Available evidence indicated that light-dependent changes in pyranine fluorescence did not originate from the apoplast of leaf cells. Microscopic observation led to the conclusion that, after prolonged feeding times or prolonged incubation, changes in pyranine fluorescence emitted from C₄ leaves reflect pH changes mainly in the cytosol of mesophyll cells. A transient acidification reaction indicated by quenching of pyranine fluorescence in the dark-light transient and not observed in C₃ species is attributed to the carboxylation of phosphoenolpyruvate. After short feeding times and in the absence of actinic illumination, CO₂ (250 l l^–1) decreased pyranine fluorescence very slowly in Amaranthus and more rapidly in C₃ leaves. After prolonged feeding times, both the rate and the extent of CO₂-dependent quenching of pyranine fluorescence increased, but the increase was insufficient to indicate the presence of highly active carbonic anhydrase in the compartment from which pyranine fluorescence was emitted. In contrast to pyranine, CDCF (pK 4.8) did not increase but rather decreased its fluorescence on illumination of an Amaranthus leaf, indicating acidification of an acidic compartment, most probably the vacuole of green leaf cells. The pattern of the acidification reaction was similar in C₄ and C₃ leaves. The remarkably large extent of the light-dependent increase in pyranine fluorescence from leaves of C₄ species and its slow kinetics are proposed to be caused by an alkalization of the cytosol which in the absence of CO₂ is larger in the mesophyll than in the bundle sheath. It gives rise to deprotonation of dye originally located in the mesophyll and, in addition, of dye which diffuses from the bundle sheath into the mesophyll following a pH gradient. Implications of slow diffusional transport of pyranine and CO₂ between mesophyll and bundle-sheath cells and the fast metabolite transport required in C₄ photosynthesis are discussed.Abbreviations CDCF 5-(and 6-)carboxy-2,7-dichlorofluorescein - DHAP dihydroxyacetone phosphate - PGA 3-phosphoglycerate This work was supported by the Sonderforschungsbereiche 176 and 251 of the University of Würzburg and by the Gottfried-Wilhelm-Leibniz Program of the Deutsche Forschungsgemeinschaft. A.S.R. was the recipient of a fellowship of the Alexander-von-Humboldt Foundation. We are grateful to Mrs. S. Neimanis for cooperation.     

Biomass production and nitrate metabolism of Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L. (C4 plant) in cultures at different levels of nitrogen supply

Summary Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C₃ plant) and Amaranthus retroflexus L. (C₄ plant) were maintained under open air conditions in standard soil at low and high nitrogen supply levels.A comparison of shoot dry weight and shoot length in the various series shows that the growth of the aboveground parts of both species was severely reduced under low N conditions. In both pure and mixed cultures the differences resulting from low N vs. high N conditions was less pronounced with Atriplex (C₃ plant) than with Amaranthus (C₄ plant). The root dry weight of the two species was not reduced so much under low N conditions as was the shoot dry weight. The low N plants were found to contain a larger proportion of their biomass in the roots than did the high N plants. In general the root proportion of Atriplex was greater than that of Amaranthus. The contents of organic nitrogen and nitrate and the nitrate reductase activity (NRA) per g dry weight of both species decreased continually throughout the experiments. With the exception of young plants, the low N plants always had tower contents of organic nitrogen and nitrate and nitrate reductase activities than did the high N plants. The highest values of NRA were measured in the leaf laminae. The eaves also exhibited the highest concentrations of organic nitrogen. The highest nitrate concentrations, however, were observed in the shoot axis, and in most cases the lowest nitrate values were found in the laminae. At the end of ne growing season this pattern was found to have been reversed with Atriplex, but not with Amaranthus. Thus Atriplex was able to maintain a higher NRA in the laminae than Amaranthus under low N conditions.The transpiration per leaf area of the C₄ plant Amaranthus during the course of a day was substantially lower than that of the C₃ plant Atriplex. There were no significant differences in transpiration between the low N and high N series of Amaranthus. The low N plants of Atriplex, however, clearly showed in most cases higher transpiration rates than the corresponding high N plants. These different transpiration rates of the high N and the low N Atriplex plants were also reflected in a distinct ¹³C discrimination.The sum of these results points to the conclusion that the C₃ plant Atriplex hortensis can maintain a better internal inorganic nitrogen supply than the C₄ plant Amaranthus retroflexus under low N conditions and an ample water supply, due to the larger root proportion and the more pronounced and flexible transpiration of the C₃ plant.Dedicated to Prof. Dr. Karl Mägdefrau, Deisenhofen, on the ocasion of his 80th birthday     

The Influence of Leaf "Windows" on Crassulacean Acid Metabolism in the South African Succulent Senecio Rowleyanus (Asteraceae)

Net CO₂ exchange rate (P_N) of shoots and diel fluctuations in titratable acidity of leaves of Senecio rowleyanus were measured to determine whether penetration of radiant energy through leaf “windows” (narrow, translucent strips on the leaf epidermis) resulted in increased CAM. Nocturnal P_N and nighttime increases in acidity were compared among plants with windows covered with reflective adhesive tape, transparent adhesive tape (to control for potential effects of the adhesive), and no tape. The windows did not significantly enhance the degree of CAM in S. rowleyanus. This revised version was published online in September 2006 with corrections to the Cover Date.     

Mitochondria from leaf mesophyll cells of C(4) plants are deficient in the H protein of glycine decarboxylase complex

Mesophyll mitochondria from green leaves of the C(4) plants Zea mays (NADP-ME-type), Panicum miliaceum (NAD-ME-type) and Panicum maximum (PEP-CK-type) oxidized NADH, malate and succinate at relatively high rates with respiratory control, but glycine was not oxidized. Among the mitochondrial proteins involved in glycine oxidation, the L, P and T proteins of glycine decarboxylase complex (GDC) and serine hydroxymethyltransferase (SHMT) were present, while the H protein of GDC was undetectable. In contrast, mesophyll mitochondria from etiolated leaves of Z. mays oxidized glycine at a slow rate and with no respiratory control, and contained the H protein as well as the other GDC proteins and SHMT. The T and P proteins and SHMT were present in the mitochondria from etiolated leaves at significantly higher levels than in those from green leaves of Z. mays. The content of the L protein was almost identical in all three C(4) plants examined and close to the value obtained for mesophyll mitochondria from the C(3) plant Pisum sativum, whereas the other GDC proteins and SHMT were less abundant than the L protein. We discuss possible reasons for the H protein's absence in mesophyll mitochondria of C(4) plants, as well as the role(s) the other GDC components could play in its absence.     

Occurrence of C3 and C4 photosynthesis in cotyledons and leaves of Salsola species (Chenopodiaceae)

Most species of the genus Salsola (Chenopodiaceae) that have been examined exhibit C₄ photosynthesis in leaves. Four Salsola species from Central Asia were investigated in this study to determine the structural and functional relationships in photosynthesis of cotyledons compared to leaves, using anatomical (Kranz versus non-Kranz anatomy, chloroplast ultrastructure) and biochemical (activities of photosynthetic enzymes of the C₃ and C₄ pathways, ¹⁴C labeling of primary photosynthesis products and ¹³C/¹²C carbon isotope fractionation) criteria. The species included S. paulsenii from section Salsola, S. richteri from section Coccosalsola, S. laricina from section Caroxylon, and S. gemmascens from section Malpigipila. The results show that all four species have a C₄ type of photosynthesis in leaves with a Salsoloid type Kranz anatomy, whereas both C₃ and C₄ types of photosynthesis were found in cotyledons. S. paulsenii and S. richteri have NADP- (NADP-ME) C₄ type biochemistry with Salsoloid Kranz anatomy in both leaves and cotyledons. In S. laricina, both cotyledons and leaves have NAD-malic enzyme (NAD-ME) C₄ type photosynthesis; however, while the leaves have Salsoloid type Kranz anatomy, cotyledons have Atriplicoid type Kranz anatomy. In S. gemmascens, cotyledons exhibit C₃ type photosynthesis, while leaves perform NAD-ME type photosynthesis. Since the four species studied belong to different Salsola sections, this suggests that differences in photosynthetic types of leaves and cotyledons may be used as a basis or studies of the origin and evolution of C₄ photosynthesis in the family Chenopodiaceae.This revised version was published online in October 2005 with corrections to the Cover Date.     

Oriented solids as a colloid suspension in nematic liquid crystal – New tool for IR-spectroscopic and structural elucidation of inorganic compounds and glasses

Possibilities of the linear-polarized infrared (IR-LD) spectroscopy of oriented colloid suspensions in nematic liquid crystals, for structural and local structural elucidation for first time are demonstrated of inorganic compounds and glasses. The advantages of the method for tellurite and borate glasses are shown. The IR-band assignment of the typical local structural units in the glasses are proposed by a comparison with the IR-characteristics of appropriate crystalline analogues as α-TeO₂, V₂O₅, MoO₃ · H₂O and its high temperature form. The IR-spectroscopic characteristics of BO₃, BO₄ and boroxol ring are elucidated, using crystalline β-BaB₂O₄, SrB₄O₇, H₃BO₃ and B₂O₃ as model systems, where the structural moieties have been refined by single crystal X-ray diffraction.     

Pollen morphological studies in subfamily Suaedoideae (Chenopodiaceae)

The pollen morphology of two Bienertia species and 28 Suaeda species from the Old World has been studied with light and scanning electron microscopy. Pollen morphological characters used in this study include pollen diameter, pore number, pore diameter, operculum diameter, chord distance, exine thickness, plus number and characteristics of exine spinules and operculum spinules. Using these characters, the pollen of Bienertia is clearly distinguished from that of Suaeda. In addition, pollen data support recent molecular studies which merge the genus Borszczowia into Suaeda. The pollen grains of Suaeda show notable variation; in some cases this allows morphological distinctions to be made between species. Taxonomically, pore number is observed to be a more useful character than pollen diameter. Principal components analysis (PCA) shows only a weak correlation between pollen characters and habit (life form), habitat, mode of photosynthesis or phylogenetic relationships. Interestingly, however, the annual C₃ and C₄ species of section Schoberia are usually characterised by a higher pore number than the perennial C₄ species.     

ATP stimulates glucose transport through activation of P2 purinergic receptors in C(2)C(12) skeletal muscle cells

Extracellular ATP acts as a signal that regulates a variety of cellular processes via binding to P2 purinergic receptors (P2 receptors). We herein investigated the effects and signaling pathways of ATP on glucose uptake in C(2)C(12) skeletal muscle cells. ATP as well as P2 receptor agonists (ATP-gamma S) stimulated the rate of glucose uptake, while P2 receptor antagonists (suramin) inhibited the stimulatory effect of ATP, indicating that P2 receptors are involved. This ATP-stimulated glucose transport was blocked by specific inhibitors of Gi protein (pertusiss toxin), phospholipase C (U73122), protein kinase C (GF109203X), and phosphatidylinositol (PI) 3-kinase (LY294002). ATP stimulated PI 3-kinase activity and P2 receptor antagonists blocked this activation. In C(2)C(12) myotubes expressing glucose transporter GLUT4, ATP increased basal and insulin-stimulated glucose transport. Finally, ATP facilitated translocation of GLUT1 and GLUT4 into plasma membrane. These results together suggest that cells respond to extracellular ATP to increase glucose transport through P2 receptors.     

Coccolithophore (–CaCO3) flux in the Sea of Okhotsk: seasonality, settling and alteration processes

Coccolithophore fluxes were determined in the Sea of Okhotsk using samples from a 1 year experiment (12 August 1990 to 12 August 1991) with sediment traps at 258 and 1061 m depth. A special study was made on Coccolithus pelagicus, using fragmentation and the degree of etching, as indicators of transport mechanisms. A Corrosion Index for C. pelagicus is developed. The coccolithophore flux pattern at 258 m depth was characterised by a strong seasonality, with flux peaks during autumn 1990 (late November to early December) and spring 1991 (March). The assemblage consisted almost entirely of the two species C. pelagicus and Emiliania huxleyi. During autumn, coccolithophore transportation to 258 m depth mainly occurred within cylindrical fecal pellets and marine snow aggregates of silicoflagellates, and through agglutination on tintinnids. Grazing caused severe fragmentation of coccoliths and disintegration of coccospheres. Marine snow aggregates contained many intact coccospheres of C. pelagicus. During spring, coccolithophores were probably removed from the euphotic zone by the ballast effect of sinking diatoms. The coccolithophore flux peak in spring occurred immediately after the ice had retreated from the trap station, and the trapped assemblage included coccoliths of subtropical species. These features indicate drifting from an ice-free location to the south or east.The coccolith and coccosphere flux at 1061 m was respectively 7 and 12 times lower than at 258 m depth, and maximum fluxes were recorded 2 months later. Increasing carbonate dissolution from 258 to 1061 m depth is expressed in the coccolithophore–CaCO₃ flux reduction of 82%, and in the increasing percentage of etched coccoliths of Coccolithus pelagicus from 32 to >90%.