Desferrioxamine-dependent iron transport in Erwinia amylovora CFBP1430: cloning of the gene encoding the ferrioxamine receptor FoxR

Iron deprivation of Erwinia amylovora CFBP1430, a species causing fire blight on Pomoïdeae, was shown to induce the production of siderophores of the desferrioxamine (dfo) family and two outer membrane polypeptides with apparent molecular weight of about 70 and 80 kDa, respectively. Cyclic dfo E was characterized as the major metabolite. Phage MudII_pR13 insertional mutagenesis and screening on CAS-agar medium yielded three dfo non-producing and one overproducing clones. These clones failed to grow in the presence of the Fe(III) chelator EDDHA and were determined further as dfo and ferrioxamine transport negative mutants, respectively. The transport mutant which appeared to lack the 70 kDa polypeptide in the outer membrane allowed the purification of dfo E. Growth under iron limitation of dfo negative mutants was stimulated with ferrioxamine E and B but not with other ferrisiderophores tested. The host DNA sequence flanking the left terminal part of the MudII_pR13 prophage responsible for the transport mutation was cloned and used to probe a parental gene library by DNA-DNA hybridization. Two recombinant cosmids restoring the transport mutation to normal were identified. Both cosmids also conferred the ability to utilize ferrioxamine B and E as iron sources on a FhuE¹ mutant of Escherichia coli. This correlated with the production of an additional polypeptide of 70 kDa in the outer membrane of E. coli transconjugants, thus confirming that this protein serves the ferrioxamine receptor function (FoxR) in E. amylovora.R. Kachadourian and A. Dellagi have contributed equally to this work.     

Transpiration and drought resistance of Douglas-fir seedlings exposed to excess ammonium

 In a pot trial growth and transpiration of 3-year-old Douglas-fir seedlings on an acid, sandy soil was examined at a deficient (30 kg N ha^{–  1} year^{–  1}) and an excessive level (120 kg N ha^{–  1} year^{–  1}) of NH₄ application. Dissolved ammonium sulphate was applied to the pots weekly for two growing seasons. In half of the pots a complete set of other nutrients was applied in optimal proportions to the applied nitrogen. Water supply was optimal and transpiration was recorded. At the end of the second treatment season irrigation was stopped for 2 weeks during dry and sunny weather. Both high application of NH₄ and additional nutrients increased shoot growth and transpiration demand in the first treatment year. The root system was smaller at higher N level and this reduced water uptake accordingly. In the second year the combination of high NH₄ ⁺ and additional nutrients affected root functioning predominantly due to salinity effects and this seriously decreased water uptake capacity and shoot water potentials, finally resulting in tree death. Without addition of other nutrients the high NH₄ ⁺ application resulted in a high degree of soil acidification, which damaged the roots, that showed a decrease in water uptake capacity. At the low NH₄ supply level soil acidification was lower, and root functioning was not affected, and the trees recovered quickly from the imposed drought. Higher needle K and P status depressed transpiration rates at the low NH₄ application rate. Received: 9 January 1995 / Accepted: 18 September 1995     

Seasonal and long-term soil water regime in West African tropical forest

Abstract. Variation of soil matric potential of a Wet Evergreen and a Moist Semi-deciduous West African forest were compared. The two forest types differed strongly in their soil water regime. Wet Evergreen forest experienced matric potentials below ?100 kPa only occasionally, while in Moist Semi-deciduous forest matric potentials were less than ?2.5 MPa for periods of several weeks or more each season. A water balance equation was used to simulate the soil water regime at both sites and predict severity and length of the dry period. The predictions showed good agreement with the field measurements of soil water potential over a 2-yr period. The methodology was used to estimate the occurrence and severity of droughts over longer periods at the two sites. The balance calculations suggest that droughts occur occasionally in the Wet Evergreen forest under study. The potential impact of droughts on species distribution and vegetation disturbance in tropical forests is discussed.     

The cellular pathway of sucrose transport in developing cotyledons ofVicia faba L. andPhaseolus vulgaris L.: a physiological assessment

The cellular pathway of sugar uptake in developing cotyledons of Vicia faba L. and Phaseolus vulgaris L. seed was evaluated using a physiological approach. The cotyledon interface with the seed coat is characterised by a specialised dermal cell complex. In the case of Vicia faba cotyledons, the epidermal component of the dermal cell complex is composed of transfer cells. Sucrose is the major sugar presented to the outer surface of both cotyledons and it is taken up from the apoplasm unaltered. Estimated sucrose concentrations within the apparent free space of Vicia and Phaseolus cotyledons were 105 and 113 mM respectively. Rates of in-vitro uptake of [¹⁴C]sucrose by cotyledon segments or by whole cotyledons following physical removal or porter inactivation of the outer cells demonstrated that, for both Vicia and Phaseolus cotyledons, the dermal cell complexes are the most intense sites of sucrose uptake. Accumulation of [¹⁴C]sucrose in the storage parenchyma of whole cotyledons was directly affected by experimental manipulation of uptake by the outer cell layers and plasmolytic disruption of the interconnecting plasmodesmata. These findings indicated that sucrose accumulated by the dermal cell complexes is transported symplasmically to the storage parenchyma. Overall, it is concluded that the dermal cell complexes of the developing legume embryo, irrespective of the presence or absence of wall ingrowths, are the major sites for the uptake of sucrose released from the maternal tissues to the seed apoplasm. Thereafter, the accumulated sucrose is transported radially inward through the symplast to the storage parenchyma.Abbreviations AFS apparent free space - CF 5-(6)-carboxyfluorescein - CFDA 5-(6)-carboxyfluorescein diacetate - Mes 2-(N-morpholino)ethanesulfonic acid - PCMBS p-chloromercuribenzenesulfonic acid - SRG sulphorhodamine G The investigation was supported by funds from the Research Management Committee, The University of Newcastle and the Australian Research Council. One of us, R. McDonald, gratefully acknowledges the support of an Australian Postgraduate Research Award. We are grateful to Stella Savoury for preparing the photomicrographs.     

Root water uptake of field-growing plants indicated by measurements of natural-abundance deuterium

Measurements of stable-isotope ratios of water extracted from stems and, in some studies, soils are increasingly being used to study the integrated root function of field-growing plants. This study explored if additional measurements on water extracted from roots could indicate the activity of roots in different areas of the soil profile and their influence on canopy water sources, so providing advantages over more common sampling strategies. Studies were conducted on trees and shrubs located in diverse habitats: a saline, semi-arid floodplain, a subhumid mountain-range front and a cold desert. At each site, roots, soil immediately surrounding the roots, and plant stems were sampled. Roots were taken from different depths in the soil, to approximately 2 m at one site. Overall, 80% of roots sampled had H isotope ratios different from the surrounding soil. The differences up to 37, were significant (p<0.05) at two of the sites. Thus water in most of the roots sampled did not come entirely, if at all, from the surrounding soil, illustrating movement and possible mixing of water within the root system. This condition was not simply related to the availability of water surrounding the soil, which was also measured. There were also differences in root and stem H isotope ratios (up to 17) in 67% of samples, although the difference was only significant in shallow samples from the floodplain. The general similarity in stem and root ²H values indicates that most roots sampled were involved in the main supply of water to the canopy. Patterns of root function varied between the individual sites. Trees were primarily using groundwater at the floodplain and mountain front sites, as the surface soils had mean matric potentials of-1800 kPa. At the mountain front site, the surface roots were transporting groundwater to the canopy in isolation form the surrounding soil. In contrast, surface roots at the floodplain were taking up water from the surrounding soil, although this water was not a significant source in the trees' overall water supply. This activity of surface roots would not have been evident from the ²H data without the root samples. At the cold desert the roots in moist surface soil provided the main source of water for the shrubs. There too the root data indicated different water uptake patterns than otherwise would have been assumed. The root data showed that groundwater could not have been a water source, a conclusion which had been reached in a previous study. Thus measurements of stable isotope ratios in root water may be a valuable tool in assessing water uptake patterns and root function.     

Transport of bacterial inoculants through intact cores of two different soils as affected by water percolation and the presence of wheat plants

Abstract Water flow-innduced transport of Burkholderia cepacia strain P2 and Pseudomonas fluorescens strain R2f cells through intact cores of loamy sand and silt loam field soils was measured for two percolation regimes, 0.9 and 4.4 mm h⁻¹, applied daily during 1 hour. For each strain, transport was generally similar between the two water regimes. Translocation of B. cepacia , with 4.4 mm h⁻¹, did occur initially in both soils. In the loamy sand soil, no change in the bacterial distribution occurred during the experiment (51 days). In the silt loam, B. cepacia cell numbers in the lower soil layers were significantly reduced, to levels at or below the limit of detection. Transport of P. fluorescens in both soils also occurred initially and was comparable to that of B. cepacia . Later in the experiment, P. fluorescens was not detectable in the lower soil layers of the loamy sand cores, due to a large decrease in surviving cell numbers. In the silt loam, the inoculant cell distribution did not change with time. Pre-incubation of the inoculated cores before starting percolation reduced B. cepacia inoculant transport in the loamy sand soil measured after 5 days, but not that determined after 54 days. Delayed percolation in the silt loam soil affected bacterial transport only after 54 days. The presence of growing wheat plants overall enhanced bacterial translocation as compared to that in unplanted soil cores, but only with percolating water. Percolation water from silt loam cores appeared the day after the onset of percolation and often contained inoculant bacteria. With loamy sand, percolation water appeared only 5 days after the start of percolation, and no inoculant bacteria were found. The results presented aid in predicting the fate of genetically manipulated bacteria in a field experiment.     

Statistical analysis of algal and water quality data

Data on cyanobacteria (blue-green algae) are generallycollected on a reactive basis, frequently in responseto bloom events. Such data presents a biased andincomplete snapshot of water quality. This paper looksat two typical data sets for UK waters showing thatwhile statistics may be used to describe the data theyare of limited use in forecasting. Suggestions ofappropriate tests for small and sparse data sets aremade.     

The generation of metabolic energy by solute transport

Secondary metabolic-energy-generating systems generate a proton motive force (pmf) or a sodium ion motive force (smf) by a process that involves the action of secondary transporters. The (electro)chemical gradient of the solute(s) is converted into the electrochemical gradient of protons or sodium ions. The most straightforward systems are the excretion systems by which a metabolic end product is excreted out of the cell in symport with protons or sodium ions (energy recycling). Similarly, solutes that were accumulated and stored in the cell under conditions of abundant energy supply may be excreted again in symport with protons when conditions become worse (energy storage). In fermentative bacteria, a proton motive force is generated by fermentation of weak acids, such as malate and citrate. The two components of the pmf, the membrane potential and the pH gradient, are generated in separate steps. The weak acid is taken up by a secondary transporter either in exchange with a fermentation product (precursor/product exchange) or by a uniporter mechanism. In both cases, net negative charge is translocated into the cell, thereby generating a membrane potential. Decarboxylation reactions in the metabolic breakdown of the weak acid consume cytoplasmic protons, thereby generating a pH gradient across the membrane. In this review, several examples of these different types of secondary metabolic energy generation will be discussed.     

Calcium fluxes at plasmalemma and tonoplast

Abstract. An account is given of the characterization of calcium fluxes across plasmalemma and tonoplast membranes of root cortical cells, using compartmental analysis. Some of the assumptions associated with the method are discussed. Recent evidence regarding the concentration of free Ca²⁺ in plant cells, and the mechanisms driving active calcium transport across cell membranes, is reviewed. It is proposed that the evidence from whole cell studies and work at the molecular level is mutually supportive, and some speculation is ventured about the general pattern of calcium transport in higher plant cells.     

The transport of morphologically abnormal sperm in the female reproductive tract of mice

Mice of the PL/J strain exhibit a high percentage of morphologically abnormal sperm and provide a model for studying the function of abnormal sperm. The ability of such sperm to reach the site of fertilization within the female reproductive tract has been investigated. We have found a decrease in the percentage of structurally abnormal sperm within the population that reaches the oviduct. This observation suggests either that there is an active selection against abnormal sperm or that they are physiologically disadvantaged in reaching the site of fertilization.