The impact of molecular systematics on hypotheses for the evolution of root nodule symbioses and implications for expanding symbioses to new host plant genera

Current taxonomic schemes place plants that can participate in root nodule symbioses among disparate groups of angiosperms. According to the classification scheme of Cronquist (1981) which is based primarily on the analysis of morphological characters, host plants of rhizobial symbionts are placed in subclasses Rosidae and Hamamelidae, and those of Frankia are distributed among subclasses Rosidae, Hamamelidae, Magnoliidae and Dilleniidae. This broad phylogenetic distribution of nodulated plants has engendered the notion that nitrogen fixing endosymbionts, particularly those of actinorhizal plants, can interact with a very broad range of unrelated host plant genotypes. New angiosperm phylogenies based on DNA sequence comparisons reveal a markedly different relationship among nodulated plants and indicate that they form a more coherent group than has previously been thought (Chase et al., 1993; Swensen et al., 1994; Soltis et al., 1995). Molecular data support a single origin of the predisposition for root nodule symbiosis (Soltis et al., 1995) and at the same time support the occurrence of multiple origins of symbiosis within this group (Doyle, 1994; Swensen, 1996; Swensen and Mullin, In Press).     

A Phylogenetic Analysis of Families in the Hamamelidae

A cladistic analysis of the families in the Hamamelidae is made in the present paper. As a monophyletic group, the subclass Hamamelidae includes 19 families, namely, the Trochodendraceae, Tetracentraceae, Cercidiphyllaceae, Eupteleaceae, Eucommiaceae, Hamamelidaceae (incl. Rhodoleiaceae and Altingiaceae), Platanaceae, Daphniphyllaceae, Balanopaceae, Didymelaceae, Myrothamnaceae, Buxaceae, Simmondsiaceae, Casuarinaceae, Fagaceae (incl. Nothofagaceae), Betulaceae, Myricaceae, Rhoipteleaceae and Juglandaceae. The Magnoliaceae was selected for outgroup comparison after careful consideration. Thirty-two informative character states were used in this study. Three principles, namely, outgroup comparison, fossil evidence and generally accepted viewpoints of morphological evolution, were used for polarization of the characters. An incompatible number concept was first introduced to evaluate the reliable degree of polarization of the characters and, by this method, the polarization of the three character states was corrected. A data matrix was constructed by the 19 ingroup families and 32 character states. The data matrix was analysed with the Minimal Parallel Evolutionary Method, Maximal Same Step Method (Xu 1989), and Synthetic Method. Three cladograms were constructed and a parsimonious cladogram (Length= 131)was used as the base for discussing the systematic relationships of families in the Hamamelidae. According to the cladogram, the earlist group differented in the subclass Hamamelidae consists of two vesselless wood families, the Trochodendraceae and Tetracentraceae. This result supports the concept proposed by Takhtajan (1987)and Cronquist (1981, 1988)that the Trochodendrales is probably a primitive taxon in the Hamamelidae. As in a clade group, the Cercidiphyllaceae, Eucommiaceae, Balanopaceae and Didymelaceae originated apparently later than the Trochodendrales. The Cercidiphyllaceae diverged earlier in this group, which implies that this family and the Trochodendrales form a primitive group in the subclass. The Cercidiphyllaceae is either placed in Hamamelidales (Cronquist 1981, Thorne 1983), or treated as an independent order (Takhtajan 1987).This analysis suggests that the Cercidiphyllaceae is a relatively isolated taxon, far from the Hamamelidaceae but close to the Trochodendrales in relation. The Eucommiaceae and Didymelaceae are both isolated families and considered as two distinct orders (Takhtajan 1987, Cronquist 1981, 1988).The Balanopaceae is included in the Fagales (Cronquist 1981, 1988) or Pittosporales (Thorne 1983), or treated as a distinct order Balanopales (Takhtajan 1987 ).Obviously the Balanopaceae and Eucommiaceae are not closely related because of the sole synapomorphy (placentation).In fact these four families are more or less isolated taxa and it is probably more reasonable to treat them as independent orders. Cronquist ( 1981, 1988) places the Eupteleaceae, Platanaceae and Myrothamnaceae in the Hamamelidales, while Takhtajan (1987)puts Hamamelidaceae and Platanaceae into the Hamamelidales and treats the Eupteleaceae and Myrothamnaceae as two independent monofamilial orders. These three families are grouped by more synapomorphies (palmateveined, serrate or lobate leaves, deciduous and anemophilous plants)which may indicate their close phylogenetical affinity. A core group of the Hamamelidae includes ten families, among which the Hamamelidaceae originated earlier than the others, so that it is a relatively primitive family. The Betulaceae, Fagaceae and Myricaceae differentiated later than the Hamamelidaceae. The former two are very closely related, and thus thought to be two neighbouring orders by Takhtajan (1987)or included in the Fagales by Cronquist (1981, 1988)and Thorne (1983). The Myricaceae and Fagaceae are connected in the cladogram by only a single synapomorphy (endosperm absent), and therefore the close relationship does not exist between them. The Buxaceae, Simmondsiaceae and Daphniphyllaceae form an advanced group, in which they are weakly linked with each other by only one synapomorphy (pollen grains＜25μm). The Daphniphyllaceae is closely related to the Simmondsiaceae, but the Buxaceae is rather isolated. The Rhoipteleaceae and Juglandaceae share a number of synapomorphies (axile placentation, endosperm absent, embryo larger, fruit indehiscent) , forming a highly specialized group. The opinion that the Juglandales is composed of the Juglandaceae and Rhoipteleaceae(Cronquist 1981; 1988, Lu et Zhang 1990)is confirmed by this analysis. A contrary point of view, which treated them as two distinct orders by Takhtajan (1987), apparently could not be accepted. The Casuarinaceae was regarded as the primitive angiosperm (Engler 1893), but in fact it is a highly reduced and specialized group. It is united with Rhoipteleaceae and Juglandaceae by four synapomorphies, i. e. placentation type, endosperm absent, embryo large and fruit indehiscent. However, the family presents six autapomorphies, and thus the position of the Casuarinaceae as an advanced family is confirmed by this analysis. Finally a strict consensus tree, which represents the phylogenetic relationships of thefamilies in the Hamamelidae, was given as a result of the analysis.     

A Revaluation of the Systematic Positions of the Cercidiphyllaceae and Daphniphyllaceae Based on rbcL Gene Sequence Analysis,with Reference to the Relationship in the “Lower” Hamamelidae

The rbcL gene sequences of six species representing five subfamilies of the Hamamelidaceae and the Platanaceae were determined and used in the phylogenetic analysis on the “lower” Hamamelidae sensu Endress (1989) and its allies newly suggested. Four most parsimonious trees were obtained, all having 893 steps with CI = 0.558 and RI = 0.591. The families Cercidiphyllaceae, Daphniphyllaceae, Hamamelidaceae and Saxifragaceae are closely located, while the relationships among them remain unsolved even if more representatives of the Hamamelidaceae were further added in this parsimony analysis. Our results confirm the phylogenetic trees revealed by Chase et al. (1993) and Soltis et al. (1997), instead of those of Hoot and Crane (1996). Considering the morphological features they share, it is suggested that the Cercidiphyllaceae and Daphniphyllaceae be placed into the Hamamelidales. The relationship between the Platanaceae and the Hamamelidaceae shown in our analysis is not so closed as suggested by the cladistic analyses by using morphological characters only(e.g. Lu et al., 1991), while those among the Platanaceae, Trochodendraceae and Tetracentraceae are close as indicated by this study. The Eupteleaceae falls into the Ranunculales. The Eucommiaceae seems to show closer relationship with the Hamamelidaceae, the “core” family of the “lower” Hamamelidae, than with the other members except the Cercidiphyllaceae. The rbcL gene trees imply that the “lower” Hamamelidae is a heterogeneous group,composed of isolated ancient families.     

Phylogenetic relationships in the Hamamelidaceae: Evidence from the nucleotide sequences of the plastid genematK

The Hamamelidaceae is a family that bridges the basal elements of the Rosidae and the lower Hamamelidae, thus a better understanding of the phylogeny of the family is important for clarifying evolutionary patterns in the diversification of eudicots. However, subfamilial as well as tribal relationships in the Hamamelidaceae have been controversial. Nucleotide sequences of the chloroplast genematK were used to study the intergeneric relationships of the family. In the phylogenetic trees, constructed using parsimony analysis, the clade containingAltingia andLiquidambar (Altingioideae) is sister to a clade that includes all other Hamamelidaceae.Exbucklandia andRhodoleia form a clade, suggesting a close relationship between the two genera.Disanthus is sister to the monophyletic Hamamelidoideae. The paraphyletic arrangement ofDisanthus, Mytilaria andExbucklandia with respect to the Hamamelidoideae does not support the combination of these genera in one subfamily. In the Hamamelidoideae, thematK phylogeny supports the monophyly of several previously recognized groups with modifications, including the tribes Eustigmateae (incl.Molinadendron), Fothergilleae (excl.Molinadendron andMatudaea), and the subtribe Dicoryphinae. However, the Hamamelideae as traditionally circumscribed is polyphyletic. Apetaly has evolved three times independently in the Hamamelidoideae.     

Molecular phylogeny of the actinorhizal Hamamelidae and relationships with host promiscuity towards Frankia

Several of the most studied actinorhizal symbioses involve associations between host plants in the subclass Hamamelidae of the dicots and actinomycetes of the genus Frankia. These actinorhizal plants comprise eight genera distributed among three families of ‘higher’ Hamamelidae, the Betulaceae, Myricaceae, and Casuarinaceae. Contrasting promiscuity towards Frankia is encountered among the different actinorhizal members of these families, and a better assessment of the evolutionary history of these actinorhizal taxa could help to understand the observed contrasts and their implications for the ecology and evolution of the actinorhizal symbiosis. Complete DNA sequences of the chloroplast gene coding for the large subunit of ribulose 1,5-bisphosphate carboxylase (rbcL) were obtained from taxa representative of these families and the Fagaceae. The phylogenetic relationships among and within these families were estimated using parsimony and distance-matrix approaches. All families appeared monophyletic. The Myricaceae appeared to derive first before the Betulaceae and the Casuarinaceae. In the Casuarinaceae, the genus Gymnostoma derived before the genera Casuarina and Allocasuarina, which were found closely related. The analysis of character-state changes in promiscuity along the consensus tree topology suggested a strong relationship between the evolutionary history of host plants and their promiscuity toward Frankia. Indeed, the actinorhizal taxa that diverged more recently in this group of plants were shown to be susceptible to a narrower spectrum of Frankia strains. The results also suggest that the ancestor of this group of plant was highly promiscuous, and that evolution has proceeded toward narrower promiscuity and greater specialization. These results imply that a tight relationship between the phytogenies of both symbiotic partners should not be expected, and that host promiscuity is likely to be a key determinant in the establishment of an effective symbiosis.     

Relationships of Droseraceae: a cladistic analysis of rbcL sequence and morphological data

Molecular support for the monophyly of Droseraceae and its phylogenetic relationships to other dicot families was investigated using parsimony analysis of nucleotide sequences of the large subunit of ribulose-1,5-bisphosphate carboxylase (rbcL). Analysis of 100 species of plants including families of subclasses Rosidae, Hamamelidae, Dilleniidae, and Caryophyllidae (sensu Cronquist) placed monophyletic Droseraceae in the same clade as Caryophyllidae and Nepenthaceae (Dilleniidae). In a second analysis of 14 species of Droseraceae, 15 caryophyllids, one Nepenthaceae, and three Santalales, a single most-parsimonious tree was found in which Droseraceae are monophyletic, although the position of Drosophyllum as a member of Droseraceae is only weakly supported. The rbcL tree identified four major lineages within genus Drosera: 1) Dionaea; 2) the regia-clade that contains only Drosera regia; 3) the capensis-clade that contains the South African and temperate species outside of Australia; and 4) the peltata-clade that consists of principally Australian endemics. A separate analysis of 14 morphological and phytochemical characters is in general agreement with the rbcL tree except for the placement of Nepenthes, Drosophyllum, and Drosera burmanni. A combined analysis of both data sets places Drosophyllum in a clade with Triphyophyllum (Dioncophyllaceae).     

Phylogenetic relationships of theJuglandaceae

A cladistic analysis of molecular data from the chloroplast generbcL was used to examine the taxonomic relationships of the walnut family (Juglandaceae). In addition, chemical and morphological data from a previous study byHufford (1992) were incorporated, expanded, and analyzed independently and in combination with the molecular data. The results of these analyses suggest that theJuglandaceae are more closely related to theFagaceae, Betulaceae, Casuarinaceae, andUrticaceae and their relatives (sensuCronquist 1981) than they are to theAnacardiaceae (sensuThorne 1983). However, sequence data fromrbcL also suggest a relationship between the higherHamamelidae and certain families in theRosidae sensuCronquist 1981 (such asRosaceae andRhamnaceae), an outcome which would add credence to the widely accepted view of the polyphyletic nature of theHamamelidae.     

Phylogenetic relationships in Saxifragaceae sensu lato: A comparison of topologies based on 18S rDNA and rbcL sequences

Relationships among the morphologically diverse members of Saxifragaceae sensu lato were inferred using 130 18S rDNA sequences. Phylogenetic analyses were conducted using representatives of all 17 subfamilies of Saxifragaceae sensu lato, as well as numerous additional taxa traditionally assigned to subclasses Magnoliidae, Caryophyllidae, Hamamelidae, Dilleniidae, Rosidae, and Asteridae. This analysis indicates that Saxifragaceae should be narrowly defined (Saxifragaceae sensu stricto) to consist of ~30 herbaceous genera. Furthermore, Saxifragaceae s. s. are part of a well-supported clade (referred to herein as Saxifragales) that also comprises lteoideae, Pterostemonoideae, Ribesioideae, Penthoroideae, and Tetracarpaeoideae, all traditional subfamilies of Saxifragaceae sensu lato, as well as Crassulaceae and Haloragaceae (both of subclass Rosidae). Paeoniaceae (Dilleniideae), and Hamamelidaceae, Cercidiphyllaceae, and Daphniphyllaceae (all of Hamamelidae). The remaining subfamilies of Saxifragaceae sensu lato fall outside this clade. Francoa (Francooideae) and Bauera (Baueroideae) are allied, respectively, with the rosid families Greyiaceae and Cunoniaceae. Brexia (Brexioideae), Parnassia (Parnassioideae), and Lepuropetolon (Lepuropetaloideae) appear in a clade with Celastraceae. Representatives of Phyllonomoideae, Eremosynoideae, Hydrangeoideae, Escallonioideae, Montinioideae, and Vahlioideae are related to taxa belonging to an expanded asterid clade (Asteridae sensu lato). The relationships suggested by analysis of 18S rDNA sequences are highly concordant with those suggested by analysis of rbcL sequences. Furthermore, these relationships are also supported in large part by other lines of evidence, including embryology. serology, and iridoid chemistry.     

CLADISTICS OF THE MAGNOLIIDAE

Abstract A cladistic resolution is presented for the origin of the angiosperms based on a parsimony analysis of 49 taxa of Magnoliidae. Hamamelidae and Alismatidae, with gymnospermous outgroup comparisons for the polarization of 104 characters. The Magnoliidae is recognized as a paraphyletic assemblage of nine orders: Calycanthales, Magnoliales, Laurales, Illiciales, Lactoridales. Ranunculales, Aristolochiales, Piperales and Nymphaeales. The Calycanthaceae and Idiospermaceae are segregated as the new order Calycanthales, which is hypothesized to be the archetype for angiosperms. Excluding Winteraceae and Lactoridaceae, the Magnoliales is monophyletic. The Austrobaileyaceae is a first branch of Magnoliales, rather than lauralean. Excluding Amborellaceae and Calycanthales, the Laurales is monophyletic. The Chloranthaceae is a first branch of Laurales, rather than piperalean. The Amborellaceae and Winteraceae are early branches of Illiciales. The Lactoridaceae is isolated as the Lactoridales. Including Papaveraceae, the Ranunculales is monophyletic, with Lardizabalaceae as a first branch. The Ranunculales is more closely related to the Hamamelidae, forming the clade Tricolpates. The Aristolochiales, Piperales and Nymphaeales are successively more closely related to the Alismatidae, forming the clade Paleoherbs. The Nelumbonaceae are nymphaealean Paleoherbs, rather than Tricolpates. The Lactoridaceae is not a Paleoherb. These results support many aspects of the strobilar-flower hypothesis for the origin of the angiosperms, as well as the plesiomorphic character states of woody shrubs with simple, pinnatelyveined leaves.     

Interesterification of phosphatidylcholine with lipases in organic media

Summary Lipases were investigated with respect to their ability to catalyse the incorporation of fatty acids into phosphatidylcholine (PC) by interesterification reactions. The enzymes were dried onto solid support materials and the conversions were carried out in water-saturated toluene. Three lipases (two fungal and one plant enzyme) had the desired activity; immobilized lipase from Mucor miehei (Lipozyme) was the most active enzyme. The Lipozyme-catalysed interesterification was selective for the sn-1 position of PC and during 48 h of reaction around 50% of the fatty acids in this position were replaced with heptadecanoic acid, a fatty acid which was practically absent in the original phospholipid. Due to adsorption on the support material and the competing hydrolysis reaction the total amount of PC in the reaction solution decreased to about 40% of the original amount. Higher interesterification rates were obtained with free fatty acids as acyl donors than with fatty acid esters. Offprint requests to: I. Svensson     

TheUlmaceae, one family or two? Evidence from chloroplast DNA restriction site mapping

The Ulmaceae is usually split into two subgroups, referred to as either tribes or more commonly subfamilies (Ulmoideae andCeltidoideae). The two groups are separated, with some exceptions, on the basis of leaf venation, fruit type, seed morphology, wood anatomy, palynology, chemistry, and chromosome number. Propositions to separate the two groups as distinct families have never gained general acceptance. Recent morphological and anatomical data have suggested, however, that not only is family status warranted but thatCeltidaceae are more closely related toMoraceae and otherUrticales than toUlmaceae. In order to test these alternative sets of relationships, restriction site mapping of the entire cpDNA was done with nine rare cutting enzymes using 11 genera ofUlmaceae s. l., three other families of theUrticales, and an outgroup family from theHamamelidae. Cladistic analysis of the data indicates thatUlmaceae s. l. is not monophyletic and that distinct families (Ulmaceae andCeltidaceae) are warranted; thatUlmaceae is the sister group toCeltidaceae plus all other families in the order; and thatCannabaceae might be nested withinCeltidaceae. Familial placements of various problematic genera (e.g.Ampelocera, Aphananthe) are resolved and character evolution of key morphological, anatomical, chemical, and chromosomal features are discussed.     

Somatic embryogenesis in <Emphasis Type="Italic">Pinus nigra</Emphasis>: embryogenic tissue initiation,maturation and regeneration ability of established cell lines

The effect of plant growth regulators (PGR), 6-benzyladenine (BA), 2,4-dichlorophenoxyacetic acid (2,4-D), α-naphthaleneacetic acid (NAA) and sugars (sucrose, maltose, glucose, fructose) on the initiation of somatic embryogenesis of Pinus nigra Arn. was investigated. Megagametophytes containing immature zygotic embryos have been used as explants. The experiments were done in the years 2000 and 2001. Higher initiation frequencies were obtained in 2001 when the zygotic embryos showed uniformity, being in the precotyledonary stage of development. Embryogenic tissue initiation occurred on all the media tested, including PGR-free medium. Relatively high initiation frequencies were obtained on media containing either NAA (9.09 %) or 2,4-D (7.14 %) alone. Somatic embryos were present as bipolar structures and showed differences in morphological features among cell lines. Plantlet regeneration occurred in cell lines containing bipolar somatic embryos composed of compact meristematic embryo “head” and suspensor organized into bundles.We highly appreciate the financial support from VEGA, Slovak Grant Agency, project No. 2/2089/22.     

The distribution and systematic relevance of the androecial character polymery

RONSE DECRAENE L. P. AND SMETS E. F., 1993. The distribution and systematic relevance of the androecial character polymery . Two characters, viz. oligomery and polymery, have been previously proposed to circumscribe the localization of the androecium. Their distribution is more or less correlated with two groups of taxa: polymery is found in Magnoliidae, Caryophyllidae, Liliatae and part of Hamamelidae; oligomery is found in Dilleniidae, Rosidae, part of Hamamelidae and Asteridae. Polymery can be described by a number of character states, which are presented in a semophyletical scheme. Spiral polyandry, i.e. a multistaminate and spiral androecium, represents the plesiomorphic condition for all Magnoliophytina and is restricted to the polymerous group. Cyclization, induced by an arrangement of the perianth in trimerous whorls and a fractioning of the continuous plastochron, leads to polycycly, i.e. an arrangement of the stamens in numerous cycles; the outer stamens are usually inserted as pairs or in alternation with the inner perianth parts. From this configuration reduction series in different groups result in androecia with a lower number of stamen whorls (such as tetracycly, tricycly, dicycly and (ob)monocycly). The transition from trimery to pentamery induces a derived stamen configuration by the merging of two tepaline whorls and the loss of some stamens. für ther reductions accompanied evolution in trimerous flowers and led to conditions resembling diplostemony as observed in Caryophyllaceae, some Hamamelidaceae and Ranunculaceae. Secondary increases, as well as reductions of stamens within a whorl must be regarded as gradual variations of each character state. Different trends affecting the number and position of the stamens can globally be traced along different lines. Polymery is consistent with other floral characters, such as the nature of perianth, vasculature (axial and cortical systems) and merosity. The androecium of a number of families and their relationships are discussed.     

Reviews of publications

Book reviewed in this article:
The Nigerian Field: Index to volumes 1–50 (1931–1985).
Fruits of South-east Asia, by Jacqueline Piper.
Grain Legumes–Evolution and Genetic Resources, by J. Smartt.
Plant Population Genetics, Breeding, and Genetic Resources, edited by A. H. D. Brown, M. T. Clegg, A. L. Kahler and B. S. Weir.
Evolution, Systematics and Fossil History of the Hamamelidae.
The Systematics Association Special Volumes 40 A&B.
Plant pheno-morphological studies in Mediterranean type ecosystems, edited by Gideon Orshan.
Molecular and Genetic Aspects of Nitrate Assimilation, edited by J. L. Wray & J. R. Kinghorn
Species dispersal in agricultural habitats, edited by R. G. H. Bunce & D. C. Howard.
Flora Iberica: plantas vasculares de la Peninsula Iberica e Islas Baleares, Vol. 2: Platanaceae–Plumbaginaceae (partim), edited by S. Castroviejo, M. Lainz, G. Lopez Gonzalez et al.     

Matrix metalloproteinase-9 and plasminogen activator inhibitor-1 are associated with right ventricular structure and function: The MESA-RV Study

Elevated resistance and reduced compliance of the pulmonary vasculature increase right ventricular (RV) afterload. Local and systemic inflammation and haemostatic abnormalities are prominent in pulmonary vascular diseases. We hypothesized that plasma biomarker levels indicating greater inflammation and coagulability associated with pulmonary vascular disease would be associated with RV structure and function measured by cardiac magnetic resonance imaging (MRI). The Multi-Ethnic Study of Atherosclerosis (MESA) performed cardiac MRI among participants aged 45–84 years without clinical cardiovascular disease. We assessed the associations of RV mass, RV end-diastolic volume (RVEDV), RV stroke volume (RVSV) and RV ejection fraction (RVEF) with plasma measures of inflammation (matrix metalloproteinase (MMP)-3 and -9, intercellular adhesion molecule (ICAM)-1, tumour necrosis factor receptor (TNF-R1), and E-selectin) and thrombosis (plasminogen activator inhibitor (PAI)-1, tissue factor, tissue factor pathway inhibitor and CD40 ligand).The study sample included 731 subjects. Higher MMP-9 levels were associated with lower RV mass before and after adjustment for left ventricular (LV) mass (p?=?0.008 and p?=?0.044, respectively). Higher levels of MMP-9 and PAI-1 were also associated with smaller RVEDV (p<0.05). Higher PAI-1 levels were associated with lower RVEF even after adjustment for LV ejection fraction (p?=?0.017). In conclusion, MMP-9 and PAI-1 are associated with changes in RV structure and function which could be potentially related to a subclinical increase in pulmonary vascular resistance.     

Juvadecene: Discovery of a juvenile hormone mimic in the plant,Macropiper excelsum

A compound with significant insect juvenile hormone activity was isolated from the plant, Macropiper excelsum. The chemical structure was determined by spectral methods to be 1-(3,4-methylenedioxyphenyl)-trans-3-decene(l), and confirmed by synthesis. The hormonally active substance applied topically to last (fifth)-instar nymphs of the milkweed bug (Oncopeltus fasciatus) induced a supernumerary metamorphosis at 30 μg. Higher doses were toxic.     

Effect of ploughing on plant species abundance and diversity in the northwestern coastal desert of Egypt

This study focuses on the effect of ploughing on plant abundance,vegetation cover, species richness, and taxonomic diversity during the growingseasons (winter and spring) of 1992 and 2000 in the habitat of inland plateau(natural habitat), 21 km south of Mersa-Matrouh (Egypt).Ninety-five species belonging to 27 families were recorded. High percentages oflife-forms and a large number of species were recorded in ploughed andunploughed stripes in the winter and spring of 2000. Higher averages of importancevalues (IVs) and absolute frequencies were recorded for most perennial andannual species in the unploughed stripes compared to the ploughed ones. This may beattributed to crop failure and consequently unfavourable soil conditions. On theother hand, some shrubby species (e.g. Noaea mucronata andHaloxylon scoparium) and perennial herbs (e.g.Gynandriris sisyrinchium) attained higher IVs in theploughed stripes compared to unploughed ones. This may be attributed to thecultivation of Prosopis juliflora trees in the elevatedpart of the ploughed stripes, which have an ecological role in protecting andenriching the soil with organic matter, thus favouring the growth of theseshrubs and perennial herbs. Higher species richness and diversity wereassociated with low concentration of dominance and low taxonomic diversity inthe spring of 2000 in ploughed and unploughed stripes compared to the winter of1992, for both perennials and annuals. The lowest taxonomic diversities wereexhibited in the spring of 2000 for ploughed and unploughed stripes where thevegetation had the largest number of congeneric species and confamilial genera.Higher species richness and diversity characterized the vegetation of theunploughed stripes, especially in winter and spring 2000, as compared to those ofploughed ones. The present study also reveals low species richness and diversityof therophytes in winter for both ploughed and unploughed stripes.     

POLLEN ENERGETICS AND POLLINATION MODES

The caloric content of pollen for several different species was determined by using a semimicro oxygen bomb calorimeter. The species studied were divided into subsets for statistical comparisons. The subsets considered were wind-pollinated dicots, monocots and gymnosperms; insect-pollinated dicots; and taxonomic subclasses of the wind-pollinated angiosperms (Asteridae, Hamamelidae, Caryophyllidae and Commelinidae). The results indicated a statistically significant caloric content difference (0.05 or higher) between wind-pollinated dicots vs. monocots and gymnosperms. There was no statistical difference between wind-pollinated dicots and insect-pollinated dicots. All subclasses were significantly different from one another. A statistically significant difference was found between two tribes in the Asteraceae which have shifted from insect to wind pollination, providing additional evidence for an independent evolution of the two. The need for future research in this area is discussed.     

Circulating trimethylamine N‐oxide and the risk of cardiovascular diseases: a systematic review and meta‐analysis of 11 prospective cohort studies

Circulating trimethylamine N‐oxide (TMAO), a canonical metabolite from gut flora, has been related to the risk of cardiovascular disorders. However, the association between circulating TMAO and the risk of cardiovascular events has not been quantitatively evaluated. We performed a systematic review and meta‐analysis of all available cohort studies regarding the association between baseline circulating TMAO and subsequent cardiovascular events. Embase and PubMed databases were searched for relevant cohort studies. The overall hazard ratios for the developing of cardiovascular events (CVEs) and mortality were extracted. Heterogeneity among the included studies was evaluated with Cochran's Q Test and I² statistics. A random‐effect model or a fixed‐effect model was applied depending on the heterogeneity. Subgroup analysis and meta‐regression were used to evaluate the source of heterogeneity. Among the 11 eligible studies, three reported both CVE and mortality outcome, one reported only CVEs and the other seven provided mortality data only. Higher circulating TMAO was associated with a 23% higher risk of CVEs (HR = 1.23, 95% CI: 1.07–1.42, I² = 31.4%) and a 55% higher risk of all‐cause mortality (HR = 1.55, 95% CI: 1.19–2.02, I² = 80.8%). Notably, the latter association may be blunted by potential publication bias, although sensitivity analysis by omitting one study at a time did not significantly change the results. Further subgroup analysis and meta‐regression did not support that the location of the study, follow‐up duration, publication year, population characteristics or the samples of TMAO affect the results significantly. Higher circulating TMAO may independently predict the risk of subsequent cardiovascular events and mortality.     

Metabolic analysis of acetate accumulation during xylose consumption by<Emphasis Type="Italic"> Paenibacillus polymyxa</Emphasis>

Paenibacillus polymyxa ATCC 12321 produced more acetic acid and less butanediol from xylose than from glucose. The product yields from xylose were ethanol (0.72 mol/mol sugar), (R,R)-2,3-butanediol (0.31 mol/mol sugar), and acetate (0.38 mol/mol sugar) while those from glucose were ethanol (0.74 mol/mol sugar), (R,R)-2,3-butanediol (0.46 mol/mol sugar), and acetate (0.05 mol/mol sugar). Higher acetate kinase activity and lower acetate uptake ability were found in xylose-grown cells than in glucose-grown cells. Furthermore, phosphoketolase activity was higher in xylose-grown cells than in glucose-grown cells. In fed-batch culture on xylose, glucose feeding raised the butanediol yield to 0.56 mol/mol sugar and reduced acetate accumulation to 0.04 mol/mol sugar.