A first assessment of genetic variation in Welwitschia mirabilis Hook

Welwitschia mirabilis is a monotypic member of the family Welwitchiaceae which, along with Ephedra and Gnetum species, comprises the gymnospermous order Gnetales. While the monophyly of this order is now widely accepted, the relationship of the Gnetales to other seed plants is still contentious. Despite the unique phylogenetic position of W. mirabilis and its extraordinary physiological and anatomical adaptations, little is known about the plant's phylogeny or its current distribution in isolated locations throughout the Namib Desert. As a preliminary step in the design of an more extensive phylogeographic study, we analyzed 37 random amplified polymorphic DNA (RAPD) loci from 59 plants distributed among five sites separated by distances of 6-440 km. Cluster analysis and analysis of molecular variance (AMOVA) revealed significant levels of variation within and between populations and little evidence of inbreeding. Genetic differences between populations reflect the geographic distances separating them. Three of the populations formed discernable genetic clusters, suggesting that little gene flow occurs between populations separated by > or = 18 km. In contrast, gene flow is occurring between two populations separated by only 6 km, supporting previous observations that pollen dispersal is primarily local and that seeds are not readily wind-born over the large distances separating most W. mirabilis populations. As a working hypothesis, we propose that W. mirabilis had a continuous distribution across its current range as much as 105 million years ago, and that as a consequence of subsequent drying trends and physical disturbance, populations became progressively isolated, accounting for their current distribution.     

Water Relations,CO2 Exchange,Water-use Efficiency and Growth of Welwitschia mirabilis Hook. fil. in three Contrasting Habitats of the Namib Desert1

CO₂ exchange, transpiration and leaf water potential of Welwitschia mirabilis were measured in three contrasting habitats of the Namib desert. From these measurements stomatal conductance, internal CO₂concentration and WUE were calculated. In two of the three habitats photosynthetic CO₂ uptake decreased and transpiration increased with increasing leaf age while in the third habitat CO₂ uptake increased and transpiration decreased with leaf age. Except for the stomata of young leaf sections in this habitat, stomata closed with increasing δw leading to a pronounced midday depression of CO₂ uptake. The high stomatal limitation of photosynthetic CO₂ uptake of glasshouse-grown plants was verified in the natural habitat. Photosynthetic CO₂ uptake saturated between 800 and 1300 μmol photons m^?2 s^?1depending on leaf age and habitat. CO₂ uptake had a broad temperature optimum declining significantly beyond 32 °C. Predawn leaf water potential reflected water availability and atmospheric conditions in the three habitats and ranged from ? 2.5 to ? 6.2 MPa. There was a pronounced diurnal course of leaf water potential in all habitats. During the day a gradient in water potential developed along the leaf axis with the lowest potential at the leaf's tip. With respect to whole plant balances of CO₂ exchange and transpiration, there were marked differences between Welwitschias in the three habitats. Despite a negative CO₂ balance over a period of five months, leaves in the driest habitat grew constantly at the expense of carbon reserves in the plant. Only at the wettest site did carbon gain exceed carbon demand for growth. The WUE of whole plants was insignificant in all habitats. The results were as contrasting as the habitats and plants and did not allow generalisations about adaptational features of Welwitschia mirabilis.     

The mycorrhizal status of Welwitschia mirabilis

This is the first report of the mycorrhizal status of Welwitschia mirabilis, a gymnosperm endemic to the Namib Desert. Like all other gymnosperms except the Pinaceae and Gnetaceae, W. mirabilis is associated with vesicular-arbuscular mycorrhizal (VAM) fungi. Mycorrhizal colonization of roots and the diversity and abundance of VAM species were determined at seven sites. Six sites received annual rainfall of 0–100 mm, varying widely from year to year. The seventh site experienced more predictable annual rainfall of 150–200 mm. Perennial vegetation was sparse at the six low-rainfall sites. Dry annual grasses from previous rain events were present at only three of these six sites and mean mycorrhizal colonization levels of W. mirabilis at these three sites were as high as 18%. W. mirabilis was not mycorrhizal at sites where grasses were absent. The seventh site, receiving higher rainfall, supported small trees and annual grasses in addition to W. mirabilis. Mycorrhizal colonization levels of W. mirabilis at this site were significantly higher than at the other six sites, closely paralleling those of the surrounding annual grasses. The mycorrhizal flora of W. mirabilis consisted of four Glomus species. These taxa were not unique to W. mirabilis, having been found with Stipagrostis and Cladoraphis grasses throughout the Namib and Kalahari deserts.     

The chromosomes and relationships of Welwitschia mirabilis

Summary W. mirabilis is unique in the plant kingdom by having a very peculiar habit. Its karyotype is very asymmetrical. Two of the chromosomes in the complement are satellited and this coincides with 2 nucleoli in the metabolic nuclei. The longest pair in the complement is nearly 3.25 times longer than the shortest pair. Between the two extremes there is a gradual transition in size in the karyotype. Such a karyotype has no relation (quantitative or qualitative) with those in Ephedra and Gnetum. Arguments have been advanced against interrelating Ephedra and Welwitschia through hermaphrodite flowers. Such flowers appear to be due to the sex polymorphism ensuing as the result of tetraploidy (in originally diploid-dioecious species) and do not represent therefore the ancestral condition. Only after these abnormalities are discovered in diploids they will represent atavistic mutations and then alone phyletic reliance can be placed in them. In view of the strong morphological differences the few resemblances between the three genera are possibly due to parallel evolution, because many of these are also found in other gymnosperms. The best arrangement is to treat the three genera as belonging to three distinct orders under one class.     

小麦小孢子发生过程的超微结构

采用透镜电镜技术对小麦（Ｔｒｉｔｉｃｕｍ ａｅｓｔｉｖｕｍ）小孢子发生过程进行了超微结构观察。造孢细胞时期细胞质中含有丰富的核糖体,质体和线粒体。在小孢子母细胞减数分裂过程中,有核糖体数量存在逐渐减少的现象,质体和线袜体结构在双线期／终变期和中期１简化,二分体时期,质体和线粒体形态结构基本恢复正常。结果表明,啵麦小孢子母细胞减数分裂过程中存在质体和线粒体的脱人化与再分化过程,但该过程与核糖体数量增     

CO2 gas exchange and transpiration of Welwitschia mirabilis Hook. fil. in the central Namib desert

Summary The diurnal course of CO₂ gas exchange, ¹⁴CO₂ incorporation, malate and citrate content, and traspiration of Welwitschia mirabilis were measured in one of its natural habitats, the Welwitschia-Vlakte in the central Namib desert (Namibia), in order to decide which CO₂ fixation pathway is used by this gymnosperm.The CO₂ gas exchange of Welwitschia is that of a C₃ plant under arid conditions. Younger leaf parts show a two-peaked pattern of photosynthetic CO₂ uptake whereas in older parts the morning peak is followed by net CO₂ release during the rest of the day. The maximum rates of net photosynthesis decrease from 3.4 mol m^-2 s^-1 in 1-year-old parts to 1 mol m^-2 s^-1 in 7-year-old parts. No net CO₂ uptake was detected during the night. The diurnal CO₂ balance indicates that the old leaf parts live at the expense of the younger ones. Irrigation of Welwitschia plants resulted in an increased CO₂ uptake throughout the light period with maximum rate of 4.1 mol m^-2 s^-1. ¹⁴CO₂ was only incorporated during the day.The water loss of Welwitschia by transpiration is considerable, reaching a peak value of 1.9 mmol m^-2 s^-1 around noon. Leaf conductance corresponds with the twopeaked pattern of CO₂ uptake.Although there is no sign of a crassulacean acid metabolism in Welwitschia the leaf contains rather high amounts of malate (up to 200 mol g^-1 dry matter) and citrate (up to 250 mol g^-1 dry matter), which depend on leaf age but do not show any significant day-night oscillation.In spite of all this the ¹³C values are in the range of-17.77 to-19.64. Possible reasons for such a high ¹³C content in a C₃ plant are discussed.Dedicated to Prof. H. Walter, the pioneer of ecophysiological studies in the Namib desert     

Unusual cytological patterns in microsporogenesis in a cultivar of Fuchsia

Summary Multiple and multipolar spindles are a generalized feature of microsporogenesis in a cultivar of Fuchsia. Only the first meiotic division occurs and gives rise to sporads with nine microspores. Variation in chromosomal complements of the microspores is illustrated by pollen polymorphism. Since some of these pollen grains are able to germinate, the possible breeding value of this super-reductional type of division is questionable. Hypotheses concerning this phenomenon found in the literature are discussed in the light of our results.     

辣椒雄性不育系与可育系小孢子发生的细胞学观察

为了探讨辣椒雄性不育花药败育时期和方式,以辣椒雄性不育系1442A、13733A及其可育系为试材,进行了研究。结果发现：败育现象从造孢细胞时期以后每个阶段都有发生,败育形式有造孢细胞液泡化、畸形、拉长、细胞间隙大;绒毡层细胞径向过度伸长,高度液泡化,且出现多层细胞,严重挤压小孢子母细胞,解体较晚且充塞花粉囊室;薄壁细胞取代了药室内壁、中层、绒毡层和小孢子母细胞的分化;药室内壁、中层层数增加,绒毡层细胞肥大,造孢细胞或花粉母细胞分解解体;由于花粉母细胞胼胝质壁不降解而无法释放出四分体小孢子;染色浅、细胞质被降解成空壳的单核期小孢子因缺乏营养物质而败育。     

Fimbriae of uropathogenic Proteus mirabilis

Proteus mirabilis is a common causative agent of cystitis and pyelonephritis in patients with urinary catheters or structural abnormalities of the urinary tract. Several types of fimbriae, which are potentially involved in adhesion to the uroepithelium, can be expressed simultaneously by P. mirabilis: mannose-resistant/Proteus-like (MR/P) fimbriae, P. mirabilis fimbriae (PMF), uroepithelial cell adhesin (UCA), renamed by some authors nonagglutinating fimbriae (NAF), and ambient-temperature fimbriae (ATF). Proteus mirabilis is a common cause of biofilm formation on catheter material and MR/P fimbriae are involved in this process. The considerable serious pathology caused by P. mirabilis in the urinary tract warrants the development of a prophylactic vaccine, and several studies have pointed to MR/P fimbriae as a potential target for immunization. This article reviews P. mirabilis fimbriae with regard to their participation in uropathogenesis, biofilm formation and as vaccine targets.     

Pollen germination in Welwitschia mirabilis Hook. f.: differences between the polyplicate pollen producing genera of the Gnetales

Pollen grains of the seed plant genera Ephedra L. and Welwitschia Hook. f. (Gnetales) are of similar size, shape, and have a polyplicate exine with alternating thicker and thinner regions. Ephedra pollen is considered inaperturate and the exine is shed during germination, leaving the male gametophyte naked. The shed exine curls up and forms a characteristic structure with transverse striations. Such upcurled exines have been found in situ in Early Cretaceous seeds with affinities to Ephedra. The purpose of this study was to document the germination of Welwitschia pollen and investigate whether they also discard their exine during this process.

The pollen grains of Welwitschia are monoaperturate with a distinct, distal sulcus. During germination, the sulcus splits open and the gametophyte expands to a spherical form that extends out of the exine. The pollen tube starts to grow one or two hours later and as in Ephedra, it is displaced towards one side. The exine is not shed but remains as a “cap” that partly covers the male gametophyte. Thus, in this respect the germination process is distinctly different from that in Ephedra and this study demonstrates that discharging the exine during pollen germination is unique to Ephedra, among the polyplicate pollen producing genera in the Gnetales.     

中亚鸢尾(Iris blowdowill)小孢子发生和雄配子体形成

选取中亚鸢尾为试材,通过石蜡切片的方法,对其小孢子发生和雄配子体发育进行了观察研究。中亚鸢尾花药壁发育方式为双子叶型,绒毡层为腺质;小孢子母细胞减数分裂时胞质分裂即有连续型,也有同时型。小孢子为四面体型和左右对称型,成熟花粉粒为二细胞。     

Electrotransformation of the stable L-form of Proteus mirabilis

Abstract To improve the transformability of stable protoplast type L-forms of Proteus mirabilis for recombinant plasmid DNA, conditions for efficient electrotransformation were explored. Exposing cells from the exponential phase of growth at a density of 6−8 × 10⁹/ml in electrotransformation buffer having a conductivity of 1.4 mS/cm to a field strength of 6.5 kV/cm for a mean pulse duration time of 1.2 ms reproducibly yielded transformation efficiencies in the order of 5 × 10⁴ transformants per μg of DNA. Compared to the polyethylene glycol method for transformation, electrotransformation appeared to be the method of choice for introduction of plasmid DNA into L-form cells.     

New aspects of the role of MR/P fimbriae in Proteus mirabilis urinary tract infection

Proteus mirabilis, a common cause of urinary tract infection (UTI), produces a number of different fimbriae including mannose-resistant Proteus-like fimbriae (MR/P). The precise role of different P. mirabilis fimbriae in ascending UTI has not yet been elucidated. In this study, a clinical isolate of P. mirabilis and an isogenic mutant unable to express MR/P were tested using different experimental approaches. They were tested for their ability to cause infection in an ascending co-infection model of UTI and in a haematogenous model in the mouse. In both models, the mutant was less able than the wild-type strain to colonise the lower and upper urinary tracts although infectivity was not abolished. In vitro adherence to uroepithelial cells was also assessed. Significant differences in adherence between both strains were observed at 1 h but not at 15 min post infection. We have also shown that a wild-type strain carries two copies of the mrpA gene. These data reinforce the importance of MR/P fimbriae in P. mirabilis UTI although other virulence factors may be necessary for efficient colonisation and development of infection.     

紫斑牡丹的花药发育和小孢子发生

紫斑牡丹的花药是在花芽发育的第３个年周期中,从雄蕊原厚基发育而来,花药壁按特有方式发生,主要特点是绒毡层与次生造孢细胞同源。花药由４个花粉囊组成,绒毡层属分泌型,中层３－４层,其中１－３层与药室内壁同步发育出纤维素壁加厚,并在花药成熟时宿存。小包子母细胞减数分裂同时开始,但不同时结束,分裂过程高度不同步。胞质分裂为同时型,四分体中小孢子排列呈正四面体形,减数分裂前期Ⅰ通常有Ｂ－染色体和染色体桥形。     

尿液中奇异变形杆菌耐药性变迁及监测分析

目的了解尿液中奇异变形杆菌临床分布及耐药性变迁情况,为临床医生合理选用抗生素提供理论依据。方法收集2008年至2012年住院及门诊患者尿液标本中分离的215株奇异变形杆菌,采用VITEK2 Compact全自动微生物分析仪进行鉴定及药敏试验,采用WH0NET 5.4软件进行统计分析。结果2008、2009、2010、2011和2012年分离奇异变形杆菌分别为26株（占12. 2% ）、26株（占12.2% ）、36株（占16. 9% ）、55株（占25. 8% ）和72株（占33. 8% ）,总计215株。奇异变形杆菌对呋喃妥因的耐药率最高,均〉90%,对丁胺卡那霉素和美洛培南的耐药率最低,均为0%,对左旋氧氟沙星的耐药率在2008？2011年均〉50% ,2012年为28.1% ;对哌拉西林/他唑巴坦的耐药率在2008 - 2009年均〉20%,而2010-2012年均〈5% ;头孢替坦、舒普深耐药率均〈7%。结论奇异变形杆菌的分离率从2008 -2012年呈日益增长趋势,提醒我们随着临床上大量使用抗生素,医院的感染率亦不断上升。耐药率从2008-2011年基本呈上升趋势,而在2012年有所下降,这可能与近几年本院临床严格执行抗菌药物的合理应用有关。     

广西含笑的小孢子发生及雄配子体形成的研究

对广西含笑的小孢子发生和雄配子体形成过程进行了解剖学研究.广西含笑的花药具4个花粉囊,花药壁由表皮、药室内壁、中层(3～5层)和绒毡层(1～2层)组成.绒毡层为腺质绒毡层,细胞具2至多核,到花粉成熟时自溶消失.小孢子母细胞减数分裂的胞质分裂为修饰性同时型,四分体排列方式为交叉型、对称型、"T"型(极少),成熟花粉粒具单...     

Environmental control of crassulacean acid metabolism in Welwitschia mirabilis Hook. Fil. in its range of natural distribution in the Namib desert

Summary Within the area of its natural distribution in South West Africa, Welwitschia mirabilis has a less negative ¹³C value than C₃ plants and a more negative ¹³C value than C₄ species. This indicates that Welwitschia m. assimilates CO₂ partially via CAM when growing in its natural habitat. The difference between the ¹³C values of Welwitschia m. and of the C₃ species is significant in the savanna, whereas it is only small and statistically not significant in the grassland zone. The proportion of CO₂ fixed via CAM is largest in the coastal desert zone. There was no correlation between the ¹³C values and the Cl^- or ash content of the tissue. Thus, CAM in Welwitschia m. seems not to be induced by salt stress. There is no change in the ¹³C values along the persistent Welwitschia m. leaf. The present data indicate that on a broad geographical scale in the area of distribution temperature regime, and water stress as a modifying factor, determine CAM in Welwitschia m. The ecological implications are discussed by comparing the behaviour of Welwitschia m. with other CAM, C₃ and C₄ species of the accompanying flora.     

First-time characterization of viable but non-culturable Proteus mirabilis: Induction and resuscitation

Pathogenic bacteria can enter into a viable but non-culturable (VBNC) state under unfavourable conditions. Proteus mirabilis is responsible for dire clinical consequences including septicaemia, urinary tract infections and pneumonia, but is not a species previously known to enter VBNC state. We suggested that stress-induced P. mirabilis can enter a VBNC state in which it retains virulence. P. mirabilis isolates were incubated in extreme osmotic pressure, starvation, low temperature and low pH to induce a VBNC state. Resuscitation was induced by temperature upshift and inoculation in tryptone soy broth with Tween 20 and brain heart infusion broth. Cellular ultrastructure and gene expression were examined using transmission electron microscopy (TEM) and quantitative real-time polymerase chain reaction (qPCR), respectively. High osmotic pressure and low acidity caused rapid entry into VBNC state. Temperature upshift caused the highest percentage of resuscitation (93%) under different induction conditions. In the VBNC state, cells showed aberrant and dwarf morphology, virulence genes and stress response genes (envZ and rpoS) were expressed (levels varied depending on strain and inducing factors). This is the first-time characterization of VBNC P. mirabilis. The ability of P. mirabilis pathogenic strains to enter a stress-induced VBNC state can be a serious public health threat.