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Two formerly broadly distributed woody Atriplex species now occur as fragmented populations across a range of microhabitats in the San Joaquin Valley Desert, southern California. We hypothesized that A. lentiformis and A. polycarpa exhibit inter- and intra-specific differences in their leaf and stem structural and functional traits corresponding with differences in soil salinity and aridity. Water potential, xylem structure and function and leaf traits were compared between three populations of A. lentiformis and four populations of A. polycarpa. The two species significantly differed in their xylem traits, with A. lentiformis displaying lower xylem density, wider mean and maximum vessel diameters and higher hydraulic conductivity (K s). They also differed in their leaf traits, such that A. lentiformis had larger leaves with higher specific leaf area (SLA) than A. polycarpa. Significant intra-specific differences occurred among leaf traits (leaf area, SLA) in A. lentiformis populations. In contrast, populations varied in their stem xylem structural traits (mean vessel wall thickness, mean vessel diameter, maximum vessel length) among A. polycarpa populations. Many of these differences were associated with soil salinity in A. lentiformis , and with minimum seasonal water potential in A. polycarpa. Overall, both saltbush species showed high intra- and inter-specific trait variation. This could be a critical consideration in understanding the evolution of these native species and has important implications for their conservation and restoration. [ABSTRACT FROM AUTHOR]

While many C4 lineages have Kranz anatomy around individual veins, Salsoleae have evolved the Salsoloid Kranz anatomy where a continuous dual layer of chlorenchyma cells encloses the vascular and water-storage tissue. With the aim of elucidating the evolution of C4 photosynthesis in Salsoleae, a broadly sampled molecular phylogeny and anatomical survey was conducted, together with biochemical, microscopic, and physiological analyses of selected photosynthetic types. From analyses of photosynthetic phenotypes, a model for evolution of this form of C4 was compared with models for evolution of Kranz anatomy around individual veins. A functionally C3 proto-Kranz phenotype (Proto-Kranz Sympegmoid) and intermediates with a photorespiratory pump (Kranz-like Sympegmoid and Kranz-like Salsoloid types) are considered crucial transitional steps towards C4 development. The molecular phylogeny provides evidence for C3 being the ancestral photosynthetic pathway but there is no phylogenetic evidence for the ancestry of C3-C4 intermediacy with respect to C4 in Salsoleae. Traits considered advantageous in arid conditions, such as annual life form, central sclerenchyma in leaves, and reduction of surface area, evolved repeatedly in Salsoleae. The recurrent evolution of a green stem cortex taking over photosynthesis in C4 clades of Salsoleae concurrent with leaf reduction was probably favoured by the higher productivity of the C4 cycle. [ABSTRACT FROM AUTHOR]

Temporal and spatial patterns of photosynthetic enzyme expression and structural maturation of chlorenchyma cells along longitudinal developmental gradients were characterized in young leaves of two single cell C4 species, Bienertia sinuspersici and Suaeda aralocaspica. Both species partition photosynthetic functions between distinct intracellular domains. In the C4-C domain, C4 acids are formed in the C4 cycle during capture of atmospheric CO2 by phosphoenolpyruvate carboxylase. In the C4-D domain, CO2 released in the C4 cycle via mitochondrial NAD-malic enzyme is refixed by Rubisco. Despite striking differences in origin and intracellular positioning of domains, these species show strong convergence in C4 developmental patterns. Both progress through a gradual developmental transition towards full C4 photosynthesis, with an associated increase in levels of photosynthetic enzymes. Analysis of longitudinal sections showed undeveloped domains at the leaf base, with Rubisco rbcL mRNA and protein contained within all chloroplasts. The two domains were first distinguishable in chlorenchyma cells at the leaf mid-regions, but still contained structurally similar chloroplasts with equivalent amounts of rbcL mRNA and protein; while mitochondria had become confined to just one domain (proto-C4-D). The C4 state was fully formed towards the leaf tips, Rubisco transcripts and protein were compartmentalized specifically to structurally distinct chloroplasts in the C4-D domains indicating selective regulation of Rubisco expression may occur by control of transcription or stability of rbcL mRNA. Determination of CO2 compensation points showed young leaves were not functionally C4, consistent with cytological observations of the developmental progression from C3 default to intermediate to C4 photosynthesis. [ABSTRACT FROM AUTHOR]

In subfamily Salsoloideae (family Chenopodiaceae) most species are C4 plants having terete leaves with Salsoloid Kranz anatomy characterized by a continuous dual chlorenchyma layer of Kranz cells (KCs) and mesophyll (M) cells, surrounding water storage and vascular tissue. From section Coccosalsola sensu Botschantzev, leaf structural and photosynthetic features were analysed on selected species of Salsola which are not performing C4 based on leaf carbon isotope composition. The results infer the following progression in distinct functional and structural forms from C3 to intermediate to C4 photosynthesis with increased leaf succulence without changes in vein density: From species performing C3 photosynthesis with Sympegmoid anatomy with two equivalent layers of elongated M cells, with few organelles in a discontinuous layer of bundle sheath (BS) cells (S. genistoides, S. masenderanica, S. webbii) > development of proto-Kranz BS cells having mitochondria in a centripetal position and increased chloroplast number (S. montana) > functional C3–C4 intermediates having intermediate CO2 compensation points with refixation of photorespired CO2, development of Kranz-like anatomy with reduction in the outer M cell layer to hypodermal-like cells, and increased specialization (but not size) of a Kranz-like inner layer of cells with increased cell wall thickness, organelle number, and selective expression of mitochondrial glycine decarboxylase (Kranz-like Sympegmoid, S. arbusculiformis; and Kranz-like Salsoloid, S. divaricata) > selective expression of enzymes between the two cell types for performing C4 with Salsoloid-type anatomy. Phylogenetic analysis of tribe Salsoleae shows the occurrence of C3 and intermediates in several clades, and lineages of interest for studying different forms of anatomy. [ABSTRACT FROM AUTHOR]

Globally, C4 plants dominate hot, open environments, but this general pattern is underpinned by important differences in the biogeography of C4 lineages. In particular, the species richness of C4 Poaceae (grasses) increases strongly with increasing temperature, whereas that of the major C4 eudicot group Chenopodiaceae correlates positively with aridity. Freezing tolerance is a crucial determinant of biogeographical relationships with temperature and is mediated by photodamage and cellular disruption by desiccation, but little is known about differences between C4 families. This study hypothesized that there is a greater risk of freezing damage via these mechanisms in C4 Poaceae than Chenopodiaceae, that freezing protection differs between the taxonomic groups, and that freezing tolerance of species is linked to arid habitat preference. Chlorophyll fluorescence, water relations, and freezing injury were compared in four C3 and six C4 species of Poaceae and Chenopodiaceae from the same Mongolian flora. Contrary to expectations, freezing-induced leaf mortality and photodamage were lower in Poaceae than Chenopodiaceae species, and unrelated to photosynthetic pathway. The freezing resistance of Poaceae species resulted from constitutive protection and cold acclimation and an ability to protect the photosynthetic apparatus from photodamage. Freezing protection was associated with low osmotic potential and low tissue elasticity, and freezing damage was accompanied by electrolyte leakage, consistent with cell-membrane disruption by ice. Both Chenopodiaceae and Poaceae had the potential to develop cold acclimation and withstand freezing during the growing season, which conflicted with the hypothesis. Instead, freezing tolerance was more closely associated with life history and ecological preference in these Mongolian species. [ABSTRACT FROM AUTHOR]

Aims The Nihewan Basin of North China, considered the cradle of Eastern civilization, contains a set of late Cenozoic strata and artifacts used by Homo erectus in the early Pleistocene (~1.66 Ma to 780 ka) and the cranial bones and teeth of early H. sapiens from the late middle Pleistocene (~370 to 260 ka). Palynological studies provide an opportunity to explore the living environment of early humans. Methods Palynological samples from the Hutouliang Section (~603–587 ka) of the Xiaodukou Formation of the Nihewan Basin were treated by heavy liquid flotation. Based on the palynological assemblages from the section, vegetation and climate in the Nihewan Basin were reconstructed. Important Findings The dynamic vegetation changed from temperate needle- and broad-leaved mixed forest-steppe (mainly Picea , Abies , Betula , Juglans , Artemisia and Chenopodiaceae) to conifer forest (mainly Pinus , Picea and Abies), which saw the replacement of H. erectus by early H. sapiens. The comparison of the Nihewan Basin with other human sites around the world during the same period reveals that early humans preferred to live in caves, accompanied by relatively open steppe or forest-steppe environments, inhabited by numerous mammals. Therefore, it is inferred that the emergence of dense conifer forest and the disappearance of open steppe environments in the Nihewan Basin at approximately 603–587 ka provide new evidence that early humans followed most mammals to steppe or forest-steppe environments and thus left the Nihewan Basin. These new findings not only enrich our knowledge of early human behavior, such as their diet, migration and settlement, but also fill in gaps in paleovegetation and paleoenvironmental research in the Nihewan Basin during the middle Pleistocene (780–400 ka). [ABSTRACT FROM AUTHOR]

Some species of Salsoleae (Chenopodiaceae) convert from C3 photosynthesis during the seedling stage to the C4 pathway in adult leaves. This unique developmental transition of photosynthetic pathways offers the exceptional opportunity to follow the development of the derived C4 syndrome from the C3 condition within individual plants, avoiding phylogenetic noise. Here we investigate Salsola soda, a little-studied species from tribe Salsoleae, using an ontogenetic approach. Anatomical sections, carbon isotope (δ13C) values, transcriptome analysis by means of mRNA sequencing, and protein levels of the key C4 enzyme phosphoenolpyruvate carboxylase (PEPC) were examined from seed to adult plant stages. Despite a previous report, our results based on δ13C values, anatomy and transcriptomics clearly indicate a C3 phase during the cotyledon stage. During this stage, the entire transcriptional repertoire of the C4 NADP-malic enzyme type is detected at low levels compared to a significant increase in true leaves. In contrast, abundance of transcripts encoding most of the major photorespiratory enzymes is not significantly decreased in leaves compared to cotyledons. PEPC polypeptide was detected only in leaves, correlating with increased PEPC transcript abundance from the cotyledon to leaf stage. [ABSTRACT FROM AUTHOR]

Background and Aims Diaspores of heteromorphic species may germinate at different times due to distinct dormancy-breaking and germination requirements, and this difference can influence life history traits. The primary aim of this study was to determine the effect of germination time of the two seed morphs of Suaeda corniculata subsp. mongolica on life history traits of the offspring.Methods Germinated brown and black seeds were sown on the 20th of each month from April to September in a simulated but near-natural habitat of the species. Phenological and vegetative traits of the maternal plants, and number, size and germination percentage of the offspring were determined.Key Results Germinated seeds sown late in the year produced smaller plants that had a higher proportion of non-dormant brown than dormant black seeds, and these brown seeds were larger than those produced by germinated seeds sown early in the year. The length of the seedling stage for brown seeds was shorter than that for black seeds, and the root/shoot ratio and reproductive allocation of plants from brown seeds were more variable than they were for plants from black seeds. Late-germinating brown seeds produced larger plants than late-germinating black seeds.Conclusions Altering the proportion of the two seed types in response to germination timing can help alleviate the adverse effects of delayed germination. The flexible strategy of a species, such as S. corniculata, that produces different proportions of dimorphic seeds in response to variation in germination timing may favour the maintenance and regeneration of the population in its unpredictable environment. [ABSTRACT FROM PUBLISHER]

Background and Aims Simultaneous formation of aerial and soil seed banks by a species provides a mechanism for population maintenance in unpredictable environments. Eolian activity greatly affects growth and regeneration of plants in a sand dune system, but we know little about the difference in the contributions of these two seed banks to population dynamics in sand dunes. Methods Seed release, germination, seedling emergence and survival of a desert annual, Agriophyllum squarrosum (Chenopodiaceae), inhabiting the Ordos Sandland in China, were determined in order to explore the different functions of the aerial and soil seed banks. Key Results The size of the aerial seed bank was higher than that of the soil seed bank throughout the growing season. Seed release was positively related to wind velocity. Compared with the soil seed bank, seed germination from the aerial seed bank was lower at low temperature (5/15 °C night/day) but higher in the light. Seedling emergence from the soil seed bank was earlier than that from the aerial seed bank. Early-emerged (15 April–15 May) seedlings died due to frost, but seedlings that emerged during the following months survived to reproduce successfully. Conclusions The timing of seed release and different germination behaviour resulted in a temporal heterogeneity of seedling emergence and establishment between the two seed banks. The study suggests that a bet-hedging strategy for the two seed banks enables A. squarrosum populations to cope successfully with the unpredictable desert environment. [ABSTRACT FROM AUTHOR]

Phylogenetic analysis of independent gains of C4 photosynthesis in Suaedoideae shows differences compared with other C4 lineages in amino acids of phosphoenolpyruvate carboxylase under positive selection and their position relative to functional residues.In subfamily Suaedoideae, four independent gains of C4 photosynthesis are proposed, which includes two parallel origins of Kranz anatomy (sections Salsina and Schoberia) and two independent origins of single-cell C4 anatomy (Bienertia and Suaeda aralocaspica). Additional phylogenetic support for this hypothesis was generated from sequence data of the C-terminal portion of the phosphoenolpyruvate carboxylase (PEPC) gene used in C4 photosynthesis (ppc-1) in combination with previous sequence data. ppc-1 sequence was generated for 20 species in Suaedoideae and two outgroup Salsola species that included all types of C4 anatomies as well as two types of C3 anatomies. A branch-site test for positively selected codons was performed using the software package PAML. From labelling of the four branches where C4 is hypothesized to have developed (foreground branches), residue 733 (maize numbering) was identified to be under positive selection with a posterior probability >0.99 and residue 868 at the >0.95 interval using Bayes empirical Bayes (BEB). When labelling all the branches within C4 clades, the branch-site test identified 13 codons to be under selection with a posterior probability >0.95 by BEB; this is discussed considering current information on functional residues. The signature C4 substitution of an alanine for a serine at position 780 in the C-terminal end (which is considered a major determinant of affinity for PEP) was only found in four of the C4 species sampled, while eight of the C4 species and all the C3 species have an alanine residue; indicating that this substitution is not a requirement for C4 function. [ABSTRACT FROM PUBLISHER]

Background and Aims In mature quinoa (Chenopodium quinoa) seeds, the lasting endosperm forms a micropylar cone covering the radicle. The suspensor cells lie within the centre of the cone. During the final stage of seed development, the cells of the lasting endosperm accumulate protein and lipids while the rest are crushed and disintegrated. Both the suspensor and endosperm die progressively from the innermost layers surrounding the embryo and extending towards the nucellar tissue. Ricinosomes are endoplasmic reticulum-derived organelles that accumulate both the pro-form and the mature form of cysteine endopeptidase (Cys-EP), first identified in castor bean (Ricinus communis) endosperm during germination. This study sought to identify associations between the presence of ricinosomes and programmed cell death (PCD) hallmarks in suspensor and endosperm cells predestined to die during quinoa seed development. Methods A structural study using light microscopy and transmission electron microscopy was performed. To detect the presence of Cys-EP, both western blot and in situ immunolocalization assays were carried out using anti-R. communis Cys-EP antibody. A TUNEL assay was used to determine DNA fragmentation. Results and Conclusions Except for the one or two cell layers that constitute the lasting endosperm in the mature seed, ricinosomes were found in suspensor and endosperm cells. These cells were also the site of morphological abnormalities, including misshapen and fragmented nuclei, vesiculation of the cytosol, vacuole collapse and cell wall disorganization. It is proposed that, in suspensor and endosperm cells, the early detection of Cys-EP in ricinosomes predicts the occurrence of PCD during late seed development. [ABSTRACT FROM PUBLISHER]

Background and Aims Within Chenopodioideae, Atripliceae have been distinguished by two bracteoles enveloping the female flowers/fruits, whereas in other tribes flowers are described as ebracteolate with persistent perianth. Molecular phylogenetic hypotheses suggest ‘bracteoles’ to be homoplastic. The origin of the bracteoles was explained by successive inflorescence reductions. Flower reduction was used to explain sex determination. Therefore, floral ontogeny was studied to evaluate the nature of the bracteoles and sex determination in Atripliceae. Methods Inflorescences of species of Atriplex, Chenopodium, Dysphania and Spinacia oleracea were investigated using light microscopy and scanning electron microscopy. Key Results The main axis of the inflorescence is indeterminate with elementary dichasia as lateral units. Flowers develop centripetally, with first the formation of a perianth primordium either from a ring primordium or from five individual tepal primordia fusing post-genitally. Subsequently, five stamen primordia originate, followed by the formation of an annular ovary primordium surrounding a central single ovule. Flowers are either initially hermaphroditic remaining bisexual and/or becoming functionally unisexual at later stages, or initially unisexual. In the studied species of Atriplex, female flowers are strictly female, except in A. hortensis. In Spinacia, female and male flowers are unisexual at all developmental stages. Female flowers of Atriplex and Spinacia are protected by two accrescent fused tepal lobes, whereas the other perianth members are absent. Conclusions In Atriplex and Spinacia modified structures around female flowers are not bracteoles, but two opposite accrescent tepal lobes, parts of a perianth persistent on the fruit. Flowers can achieve sexuality through many different combinations; they are initially hermaphroditic, subsequently developing into bisexual or functionally unisexual flowers, with the exception of Spinacia and strictly female flowers in Atriplex, which are unisexual from the earliest developmental stages. There may be a relationship between the formation of an annular perianth primordium and flexibility in floral sex determination. [ABSTRACT FROM AUTHOR]

Genus Suaeda (family Chenopodiaceae, subfamily Suaedoideae) has two structural types of Kranz anatomy consisting of a single compound Kranz unit enclosing vascular tissue. One, represented by Suaeda taxifolia, has mesophyll (M) and bundle sheath (BS) cells distributed around the leaf periphery. The second, represented by Suaeda eltonica, has M and BS surrounding vascular bundles in the central plane. In both, structural and biochemical development of C4 occurs basipetally, as observed by analysis of the maturation gradient on longitudinal leaf sections. This progression in development was also observed in mid-sections of young, intermediate, and mature leaves in both species, with three clear stages: (i) monomorphic chloroplasts in the two cell types in younger tissue with immunolocalization and in situ hybridization showing ribulose bisphosphate carboxylase oxygenase (Rubisco) preferentially localized in BS chloroplasts, and increasing in parallel with the establishment of Kranz anatomy; (ii) vacuolization and selective organelle positioning in BS cells, with occurrence of phosphoenolpyruvate carboxylase (PEPC) and immunolocalization showing that it is preferentially in M cells; (iii) establishment of chloroplast dimorphism and mitochondrial differentiation in mature tissue and full expression of C4 biochemistry including pyruvate, Pi dikinase (PPDK) and NAD-malic enzyme (NAD-ME). Accumulation of rbcL mRNA preceded its peptide expression, occurring prior to organelle positioning and differentiation. During development there was sequential expression and increase in levels of Rubisco and PEPC followed by NAD-ME and PPDK, and an increase in the 13C/12C isotope composition of leaves to values characteristic of C4 photosynthesis. The findings indicate that these two forms of NAD-ME type C4 photosynthesis evolved in parallel within the subfamily with similar ontogenetic programmes. [ABSTRACT FROM PUBLISHER]

Genus Suaeda (family Chenopodiaceae, subfamily Suaedoideae) has two structural types of Kranz anatomy consisting of a single compound Kranz unit enclosing vascular tissue. One, represented by Suaeda taxifolia, has mesophyll (M) and bundle sheath (BS) cells distributed around the leaf periphery. The second, represented by Suaeda eltonica, has M and BS surrounding vascular bundles in the central plane. In both, structural and biochemical development of C4 occurs basipetally, as observed by analysis of the maturation gradient on longitudinal leaf sections. This progression in development was also observed in mid-sections of young, intermediate, and mature leaves in both species, with three clear stages: (i) monomorphic chloroplasts in the two cell types in younger tissue with immunolocalization and in situ hybridization showing ribulose bisphosphate carboxylase oxygenase (Rubisco) preferentially localized in BS chloroplasts, and increasing in parallel with the establishment of Kranz anatomy; (ii) vacuolization and selective organelle positioning in BS cells, with occurrence of phosphoenolpyruvate carboxylase (PEPC) and immunolocalization showing that it is preferentially in M cells; (iii) establishment of chloroplast dimorphism and mitochondrial differentiation in mature tissue and full expression of C4 biochemistry including pyruvate, Pi dikinase (PPDK) and NAD-malic enzyme (NAD-ME). Accumulation of rbcL mRNA preceded its peptide expression, occurring prior to organelle positioning and differentiation. During development there was sequential expression and increase in levels of Rubisco and PEPC followed by NAD-ME and PPDK, and an increase in the 13C/12C isotope composition of leaves to values characteristic of C4 photosynthesis. The findings indicate that these two forms of NAD-ME type C4 photosynthesis evolved in parallel within the subfamily with similar ontogenetic programmes. [ABSTRACT FROM PUBLISHER]

Among dicotyledon families, Chenopodiaceae has the most C4 species and the greatest diversity in structural forms of C4. In subfamily Salicornioideae, C4 photosynthesis has, so far, only been found in the genus Halosarcia which is now included in the broadly circumscribed Tecticornia. Comparative anatomical, cytochemical, and physiological studies on these taxa, which have near-aphyllous photosynthetic shoots, show that T. pergranulata is C3, and that two subspecies of T. indica (bidens and indica) are C4 (Kranz-tecticornoid type). In T. pergranulata, the stems have two layers of chlorenchyma cells surrounding the centrally located water storage tissue. The two subspecies of T. indica have Kranz anatomy in reduced leaves and in the fleshy stem cortex. They are NAD-malic enzyme-type C4 species, with mesophyll chloroplasts having reduced grana, characteristic of this subtype. The Kranz-tecticornoid-type anatomy is unique among C4 types in the family in having groups of chlorenchymatous cells separated by a network of large colourless cells (which may provide mechanical support or optimize the distribution of radiation in the tissue), and in having peripheral vascular bundles with the phloem side facing the bundle sheath cells. Also, the bundle sheath cells have chloroplasts in a centrifugal position, which is atypical for C4 dicots. Fluorescence analyses in fresh sections indicate that all non-lignified cell walls have ferulic acid, a cell wall cross-linker. Structural–functional relationships of C4 photosynthesis in T. indica are discussed. Recent molecular studies show that the C4 taxa in Tecticornia form a monophyletic group, with incorporation of the Australian endemic genera of Salicornioideae, including Halosarcia, Pachycornia, Sclerostegia, and Tegicornia, into Tecticornia. [ABSTRACT FROM PUBLISHER]

C4 plants have been reported to have Rubiscos with higher maximum carboxylation rates (kcatCO2) and Michaelis–Menten constants (Km) for CO2 (Kc) than the enzyme from C3 species, but variation in other kinetic parameters between the two photosynthetic pathways has not been extensively examined. The CO2/O2 specificity (SC/O), kcatCO2, Kc, and the Km for O2 (Ko) and RuBP (Km-RuBP), were measured at 25 °C, in Rubisco purified from 16 species of Flaveria (Asteraceae). Our analysis included two C3 species of Flaveria, four C4 species, and ten C3-C4 or C4-like species, in addition to other C4 (Zea mays and Amaranthus edulis) and C3 (Spinacea oleracea and Chenopodium album) plants. The SC/O of the C4 Flaveria species was about 77 mol mol−1, which was approximately 5% lower than the corresponding value in the C3 species. For Rubisco from the C4 Flaverias kcatCO2 and Kc were 23% and 45% higher, respectively, than for Rubisco from the C3 plants. Interestingly, it was found that the Ko for Rubisco from the C4 species F. bidentis and F. trinervia were similar to the C3 Flaveria Rubiscos (∼650 μM) while the Ko for Rubisco in the C4 species F. kochiana, F. australasica, Z. mays, and A. edulis was reduced more than 2-fold. There were no pathway-related differences in Km-RuBP. In the C3-C4 species kcatCO2 and Kc were generally similar to the C3 Rubiscos, but the Ko values were more variable. The typical negative relationships were observed between SC/O and both kcatCO2 and Kc, and a strongly positive relationship was observed between kcatCO2 and Kc. However, the statistical significance of these relationships was influenced by the phylogenetic relatedness of the species. [ABSTRACT FROM PUBLISHER]

The internal conductance to CO2 transfer from intercellular spaces to chloroplasts poses a major limitation to photosynthesis, but few studies have investigated its temperature response. The aim of this study was to determine the temperature response of photosynthesis and internal conductance between 10 °C and 35 °C in seedlings of a deciduous forest tree species, Quercus canariensis. Internal conductance was estimated via simultaneous measurements of gas exchange and chlorophyll fluorescence (‘variable J method’). Two of the required parameters, the intercellular photocompensation point (Ci*) and rate of mitochondrial respiration in the light (Rd), were estimated by the Laisk method. These were used to calculate the chloroplastic photocompensation point (Γ*) in a simultaneous equation with gi. An independent estimate of internal conductance was obtained by a novel curve-fitting method based on the curvature of the initial Rubisco-limited portion of an A/Ci curve. The temperature responses of the rate of Rubisco carboxylation (Vcmax) and the RuBP limited rate of electron transport (Jmax) were determined from chloroplastic CO2 concentrations. The rate of net photosynthesis peaked at 24 °C. Ci* was similar to reports for other species with a Ci* of 39 μmol mol−1 at 25 °C and an activation energy of 34 kJ mol−1. Γ* was very similar to the published temperature response for Spinacia oleracea from 20 °C to 35 °C, but was slightly greater at 10 °C and 15 °C. Jmax peaked at 30 °C, whereas Vcmax did not reach a maximum between 10 °C and 35 °C. Activation energies were 49 kJ mol−1 for Vcmax and 100 kJ mol−1 for Jmax. Both methods showed that internal conductance doubled from 10 °C to 20 °C, and then was nearly temperature-independent from 20 °C to 35 °C. Hence, the temperature response of internal conductance could not be fitted to an Arrhenius function. The best fit to estimated gi was obtained with a three-parameter log normal function (R2=0.98), with a maximum gi of 0.19 mol m−2 s−1 at 29 °C. [ABSTRACT FROM PUBLISHER]

Predawn plant water potential (Ψw) is used to estimate soil moisture available to plants because plants are expected to equilibrate with the root-zone Ψw. Although this equilibrium assumption provides the basis for interpreting many physiological and ecological parameters, much work suggests predawn plant Ψw is often more negative than root-zone soil Ψw. For many halophytes even when soils are well-watered and night-time shoot and root water loss eliminated, predawn disequilibrium (PDD) between leaf and soil Ψw can exceed 0.5 MPa. A model halophyte, Sarcobatus vermiculatus, was used to test the predictions that low predawn solute potential (Ψs) in the leaf apoplast is a major mechanism driving PDD and that low Ψs is due to high Na+ and K+ concentrations in the leaf apoplast. Measurements of leaf cell turgor (Ψp) and solute potential (Ψs) of plants grown under a range of soil salinities demonstrated that predawn symplast Ψw was 1.7 to 2.1 MPa more negative than predawn xylem Ψw, indicating a significant negative apoplastic Ψs. Measurements on isolated apoplastic fluid indicated that Na+ concentrations in the leaf apoplast ranged from 80 to 230 mM, depending on salinity, while apoplastic K+ remained around 50 mM. The water relations measurements suggest that without a low apoplastic Ψs, predawn Ψp may reach pressures that could cause cell damage. It is proposed that low predawn apoplastic Ψs may be an efficient way to regulate Ψp in plants that accumulate high concentrations of osmotica or when plants are subject to fluctuating patterns of soil water availability. [ABSTRACT FROM PUBLISHER]

• Background and Aims The subfamily Salicornioideae (Chenopodiaceae) are a taxonomically difficult group largely due to the lack of diagnostic characters available to delineate tribal- and generic-level boundaries; a consequence of their reduced floral and vegetative features. This study examined the variation in fruits and seeds across both tribes of the Salicornioideae to assess if characters support traditional taxonomic sections.• Methods Light microscopy, environmental scanning electron microscopy and anatomical ultra-thin sectioning were employed to examine variation in fruits and seeds. Sixty-eight representatives across 14 of the 15 genera currently recognized within the tribes Halopeplideae and Salicornieae were examined to determine whether characters support current taxonomic groups.• Key Results Characters such as seed coat structure, embryo shape, seed orientation, the forms of seed storage proteins and carbohydrates show variation within the Salicornioideae and may be phylogenetically useful. The campylotropous ovule typical of the Chenopodiaceae generally results in a curved embryo; however, many Halosarcia and Sclerostegia species have straight embryos and in Salicornia and Sarcocornia the large peripheral embryo appears bent rather than curved. Seed coat ornamentation of Microcnemum and Arthrocnemum is distinct from other Salicornioideae as the elongated epidermal cells of the exotesta have convex walls. Histochemical stains of anatomical sections of cotyledon cells showed protein bodies were variable in shape, and starch grains were present in some species, namely Salicornia bigelovii, S. europaea and Allenrolfea occidentalis.• Conclusions While fruits and seeds were found to be variable within the subfamily, no synapomorphic characters support the tribe Halopeplideae as these genera have crustaceous seed coats, curved embryos and abundant perisperm; features characteristic of many of the tribe Salicornieae. The endemic Australian genera are closely related and few seed and fruit characters are diagnostic at the generic level. Nineteen characters identified as being potentially informative will be included in future phylogenetic analyses of the subfamily. [ABSTRACT FROM AUTHOR]

In higher plants the vacuolar K+‐selective (VK) channel was identified solely in guard cells. This patch‐clamp study describes a 40 pS homologue of the VK channel in Beta vulgaris taproot vacuoles. This voltage‐independent channel is activated by submicromolar Ca2+, and is ideally selective for K+ over Cl– and Na+. [ABSTRACT FROM PUBLISHER]

The Chenopodiaceae Suaeda salsa L. was grown under different salt concentrations and under osmotic stress. The fresh weight was markedly stimulated by 0.1 M NaCl, 0.4 M NaCl and 0.1 M KCl and reduced by osmotic stress (PEG iso‐osmotic to 0.1 M NaCl). Treatment with 0.4 M KCl severely damaged the plants. Membrane vesicle fractions containing tonoplast vesicles were isolated by sucrose gradient from leaves of the S. salsa plants and modulations of V‐ATPase and V‐PPase depending on the growth conditions were determined. Western blot analysis revealed that V‐ATPase of S. salsa consists of at least nine subunits (apparent molecular masses 66, 55, 52, 48, 36, 35, 29, 18, and 16 kDa). This polypeptide pattern did not depend on culture conditions. V‐PPase is composed of a single polypeptide (69 kDa). An additional polypeptide (54 kDa) was detected in the fractions of NaCl‐, KCl‐ and PEG‐treated plants. It turned out that the main strategy of salt‐tolerance of S. salsa seems to be an up‐regulation of V‐ATPase activity, which is required to energize the tonoplast for ion uptake into the vacuole, while V‐PPase plays only a minor role. The increase in V‐ATPase activity is not obtained by structural changes of the enzyme, but by an increase in V‐ATPase protein amount. [ABSTRACT FROM PUBLISHER]

Haloxylon aphyllum and H. persicum of Chenopodiaceae are dominant plants in the continental deserts of the Asian Irano-Turanian region. The photosynthetic organs, assimilating shoots and leaf-like cotyledons of these two species were studied to characterize their photosynthetic types. 13C/12C isotope ratios, the cellular anatomy of as similating organs, primary photosynthetic products, and activities of carbon metabolism enzymes, RUBP carboxylase, PEP carboxylase, malic enzymes, and aspartate aminotransferase, indicate different pathways of CO2 fixation in the photosynthetic organs. Assimilating shoots had attributes of the C4 photosynthesis entirely, while cotyledons lack Kranz-anatomy and incorporated CO2 via C3 photosynthesis. Cotyledons and seeds had lower δ13C values compared to shoots, consistent with the contribution of C3-like CO2 assimilation. Two pathways of carbon donation to the C3 cycle via decarboxylation of C4 acids in bundle sheath cells are suggested to occur in shoots of Haloxylon. The primary photosynthetic product malate can be utilized through NADP+-malic enzyme which occurs in high activity. NADδ-malic enzyme may contribute to C4 photosynthesis (some aspartate is formed as an initial product, the bundle sheath chloroplasts have some grana, and NAD+-malic enzyme is found in bundle sheath cells of shoots, all criteria for NAD+-malic enzyme type photosynthesis). We propose that organ diversity of CO2 fixation pathway in Haloxylon species is an important factor for their growth, survival and reproduction in continental climate deserts. [ABSTRACT FROM AUTHOR]

This study broke down the complex C4 photosynthesis syndrome of Camphorosmeae (Chenopodiaceae) into its constituent leaf anatomical traits, inferring independent origins of C4 and losses of succulence.Broad-scale phylogenetic studies give first insights in numbers, relationships, and ages of C4 lineages. They are, however, generally limited to a model that treats the evolution of the complex C4 syndrome in different lineages as a directly comparable process. Here, we use a resolved and well-sampled phylogenetic tree of Camphorosmeae, based on three chloroplast and one nuclear marker and on leaf anatomical traits to infer a more detailed picture of C4 leaf-type evolution in this lineage. Our ancestral character state reconstructions allowed two scenarios: (i) Sedobassia is a derived C3/C4 intermediate, implying two independent gains of C4 in Bassia and Camphorosma; or (ii) Sedobassia is a plesiomorphic C3/C4 intermediate, representing a syndrome ancestral to the Bassia/Camphorosma/Sedobassia lineage. In Bassia, a kochioid leaf type (Bassia muricata and/or Bassia prostrata type) is ancestral. At least three independent losses of water-storage tissue occurred, resulting in parallel shifts towards an atriplicoid leaf type. These changes in leaf anatomy are adaptations to different survival strategies in steppic or semi-desert habitats with seasonal rainfall. In contrast, Camphorosma shows a fixed C4 anatomy differing from Bassia types in its continuous Kranz layer, which indeed points to an independent origin of the full C4 syndrome in Camphorosma, either from an independent C3 or from a common C3/C4 intermediate ancestor, perhaps similar to its C3/C4 intermediate sister genus Sedobassia. The enlarged bundle sheath cells of Sedobassia might represent an important early step in C4 evolution in Camphorosmeae. [ABSTRACT FROM PUBLISHER]

Studies the Salsoloid-type Kranz anatomy in leaves or stems in relation to the diversity in anatomy which was found in cotyledons. Members of the family Chenopodiaceae that were used for the study; Immunolocalization studies on Rubisco; Labeling in bundle sheath cells of leavs and cotyledons of organs having Kranz anatomy; Mechanism of photosynthesis in the family Chenopodiaceae.