bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses of apple leaf stomata: a model for single leaves and a whole tree
Authors: THORPE M. R. , WARRIT B. , LANDSBERG J. J.
Published: April 2006

Abstract. An empirical model of stomatal response to environmental factors was developed from measurements of stomatal conductance (gs) made in a leaf chamber under controlled conditions. Results presented in a companion paper (Warrit, Landsberg & Thorpe, 1980) indicated that the model could be written in terms of only two factors, photon flux density (Qp) and leaf to air vapour pressure gradient (D). The response of Qp was hyperbolic and that to D linear; combining these the equation of the model is

image

where gr is a reference conductance, α is the slope of the response to D and β indicates the sensitivity of gs response to Qp. Values of α were 0.20 and 0.30 kPa−1 in June and August; the corresponding values of β were 59 and 79 μmol m−2 s−1.

The model was tested against mean values of gs obtained with a porometer in the field, using environmental measurements as inputs. Correspondence between measured and calculated values was good. Transpiration rates were calculated from the Penman‐Monteith equation, with stomatal resistance values calculated from the model, and compared with gravimetric measurements of tree water use. It was shown that transpiration could be calculated with acceptable accuracy. The effects of variations in stomatal resistance on transpiration rates under a range of conditions were explored using the model and the Penman‐ Monteith equation.
Root nodule anatomy, type of export product and evolutionary origin in some Leguminosae
Authors: SPRENT J. I. , EMBRAPA
Published: April 2006

Abstract. The tribe Phaseoleae, of the sub‐family Papi‐lionoideae of the Leguminosae shows distinct differences from the tribes Vicieae and Trifolieae in nodule morphology and anatomy. Nodules of the Phaseoleae have determinate growth as, at maturity, the vascular strands fuse at the apex forming, effectively, a closed loop of the root stele. Nodules of the Vicieae and Trifolieae have an apical meristem, hence indeterminate growth; one or more branches of the root stele enter and dichotomise within the nodule, new elements are differentiated in relation to nodule growth, and the fine branches are free at the apical end of the nodule. Nodules of the Vicieae and Trifolieae additionally have vascular transfer cells and vacuolate infected cells, and the rhizobial bacteroids are pleomorphic.

The principal export products of nitrogen fixing nodules of the Phaseoleae are the ureides allantoin and allantoic acid, whilst those of the Vicieae and Trifolieae are amides and amino acids, especially glutamine and asparagine. The advantages and disadvantages of these export products are discussed in the light of nodular vascular anatomy and in respect of the tropical/subtropical origin of the Phaseoleae and the temperate origin of the Vicieae and Trifolieae.
Measurement of hydraulic conductivity of barley roots during inhibition of ion transport by azetidine 2‐carboxylic acid
Authors: PITMAN M. G.
Published: April 2006

Abstract. Azetidine 2‐carboxylic acid inhibits ion release to the xylem and exudation from excised barley roots. This inhibition is not accompanied by reduction in hydraulic conductivity showing that the action of azetidine 2‐carboxylic acid is on ion movement across the root to the xylem.
The effect of xanthoxylin (2‐oxy, 4‐6‐dimethoxyacetophenone) on potassium‐dependent acid: extrusion in wheat and maize root segments
Authors: BELLANDO M. , ALLOATTI G. , ROMANI G. , MARRÉ M. T.
Published: April 2006

Abstract. Xanthoxylin is a cytotoxic and fungicidal compound with the characteristics of a typical phytoalexin. At a concentration of 0.3 mol m−3 it inhibits K+‐dependent acid extrusion and K+ net uptake (or uptake of equivalent alkaline cations such as Rb+ and CS+) by up to about 80% and hyperpolarizes by about 20% the membrane electrical potential. Its inhibition of the acid extrusion does not depend on altered ion exchange involving the anions in the media, a reduction of the metabolic energy available, or detectable changes in the permeability of the cell membrane to H+ ions. The drop in K+ net uptake depends on a decrease in the influx of K+ into the cell. In functional terms, xanthoxylin is an inhibitor of the K+ permeation mechanism and does not appear to interact with the mechanisms creating the electrochemical energy gradient.
A model of drop size distribution for a system with evaporation
Authors: BRAIN P. , BUTLER D. R.
Published: April 2006

Abstract. The size and shape of drops on leaf surfaces strongly affect their persistence. The relationship between volume and exposed surface area of drops on wheat leaves and the log‐normal drop size distribution in a wheat canopy after rain are used to derive equations to describe how the total volume and drop number change with evaporation. Firstly, the behaviour of a single drop as it evaporates is considered and then equations describing the change in a population of drops with an initial log‐normal distribution are derived. The time taken for all the drops to reach complete dryness is about thirty times that for the same volume of water spread uniformly over the surface with the same potential evaporation rate.
Phosphorylation of histone H1 during the cell cycle of artichoke
Authors: STRATTON B. R. , TREWAVAS A. J.
Published: April 2006

Abstract. Histones have been extracted from tuber and cultured tuber explant material and separated by gel electrophoresis. Histone H1 is heterogenous with 3–4 components in addition to the widely recognized histone H1a and H1b. Using labelling procedures and alkaline phosphatase treatment, histone H1 has been shown to be phosphorylated on both serine and threonine residues and possibly other acid‐labile linkages. Variations in histone H1 phosphorylation have been measured through the cell cycle and the evidence indicates enhanced phosphorylation occurring during the G2/M phase as in animal systems.
Cytological evidence for cytoplasmic volume control inPlatymonas subcordiformisafter osmotic stress
Authors: KIRST G. O. , KRAMER D.
Published: April 2006

Abstract.Platymonas subcordiformis, a marine phytoplankton flagellate, shows partial control of cell volume in response to osmotic stress. Electron micrographs of samples taken at short intervals after application of a hypo‐osmotic stress revealed that a large vacuolar system is formed by fusion of vesicles originating from the Golgi apparatus. The chloroplast is swollen and the thylakoid stacking is transiently disturbed for 1 to 5 min after the osmotic shock. It then regains the original size and stacked organization of the thylakoids, while the vacuoles remain permanently. It is assumed that mainly the cytoplasmic compartment is under volume control rather than the whole cell, as has been found in other wall‐less micro‐algae.
Relationship of dehydration rate to drought avoidance, dehydration tolerance and dehydration avoidance of cabbage leaves, and to their acclimation during drought‐induced water stress*
Authors: LEVITT J.
Published: April 2006

Abstract. Drought avoidance due to cuticular control increases with leaf number to a maximum in the intermediate leaves, decreasing to a minimum in the upper leaves. Dehydrated intermediate leaves do not rehydrate detectably when floated on water for several days. Excision of their petioles when submerged, permits full rehydration, presumably via the xylem. Stressing the plant by withholding water for 1–3 weeks fails to increase this already high resistance to water movement through the leaf surface. It does, however, markedly decrease the loss of water from the fully rehydrated (100% RWC) leaves during the first hour of dehydration, presumably due to a more rapid stomatal closure than in the non‐stressed leaves.

Dehydration tolerance increases with leaf number, without an intermediate maximum. The intermediate and upper leaves were markedly more tolerant of dehydration after drought‐induced stress than when non‐stressed. Dehydration tolerance in some cases, was inversely proportional to dehydration rate. It was possible, however, to equalize the rates of dehydration of drought‐stressed and non‐drought‐stressed leaves without affecting the greater tolerance of the drought‐stressed leaves.

Dehydration avoidance by osmotic adjustment was markedly developed in the slowly dehydrated attached leaves of drought‐stressed plants, but not in the rapidly dehydrated excised leaves. This is evidence of drought acclimation. It must, therefore, be concluded that the slow dehydration of the drought‐stressed plants also leads to the increase in dehydration tolerance by permitting drought‐induced acclimation.

The overall drought resistance of cabbage leaves depends on the three components: drought avoidance, dehydration avoidance and dehydration tolerance. The latter two increase during acclimation but the cuticular control of drought avoidance does not.
The evolution of educational inequalities in smoking: a changing relationship and a cross‐over effect among German birth cohorts of 1921–70
Authors: Schulze Alexander , Mons Ute
Published: May 2006

Aims  To investigate the evolution of the relationship between education and smoking behaviour (ever‐smoking and age of initiation) among German birth cohorts of 1921–70.

Participants  A total of 5297 respondents to the German Federal Health Survey of 1998 were divided into 10‐year sex–birth–education cohorts.

Measurements  Self‐reported smoking histories (ever‐smoking and the age of starting smoking). 

Findings  There was an inversion of the educational gradient around the birth cohorts of 1931–40 for men and 1941–50 for women. For men, the educational cross‐over in smoking was due to a stronger decrease of the ever‐smoking prevalence of the highly educated compared to the least educated. In women it was due to a stronger increase in ever‐smoking prevalence among the least educated compared to the highly educated. This educational cross‐over effect was also be detected for the average age of starting smoking, and involved the same cohorts. Additionally, in the youngest birth cohorts the differences between the least and highest educated of each gender were greater than the differences between the genders.

Conclusions  The educational differences in smoking prevalence are stable in men but in women they are widening. Hence, socio‐economic inequalities in health due to smoking will rise in women in the next decades, while they will stabilize in men.
Review article: uncomplicated diverticular disease of the colon
Authors: PETRUZZIELLO L. , IACOPINI F. , BULAJIC M. , SHAH S. , COSTAMAGNA G.
Published: April 2006

Diverticular disease of the colon is the fifth most important gastrointestinal disease in terms of direct and indirect healthcare costs in western countries. Uncomplicated diverticular disease is defined as the presence of diverticula in the absence of complications such as perforation, fistula, obstruction and/or bleeding. The distribution of diverticula along the colon varies worldwide being almost always left‐sided and directly related to age in western countries and right‐sided where diet is rich in fibre.

The pathophysiology of diverticular disease is complex and relates to abnormal colonic motility, changes in the colonic wall, chronic mucosal low‐grade inflammation, imbalance in colonic microflora and visceral hypersensitivity. Moreover, there can be genetic factors involved in the development of colonic diverticula.

The use of non‐absorbable antibiotics is the mainstay of therapy in patients with mild to moderate symptoms, and the effect of fibre‐supplementation alone does not appear to be significantly different from placebo, although no definite data are available.

More recently, alternative treatments have been reported. Mesalazine acts as a local mucosal immunomodulator and has been shown to improve symptoms and prevent recurrence of diverticulitis. In addition, probiotics have also been shown to be beneficial by re‐establishing a normal gut microflora. In this study, the current literature on uncomplicated diverticular disease of the colon is reviewed.
Class switch recombination in selective IgA-deficient subjects
Authors: Hummelshoj L , Ryder L P , Nielsen L K , Nielsen C H , Poulsen L K
Published: April 2006

Selective IgA deficiency is a common immunodeficiency in Caucasians, but the molecular basis of the disorder remains elusive. To address this issue we examined the molecular events leading to IgA production. Naive IgD positive B cells were purified from four donors with IgA deficiency and four control donors, all Caucasians. Stimulation of B cells from IgA-deficient donors with the cytokines transforming growth factor (TGF)-β, interferon (IFN)-γ or interleukin (IL)-10 in the presence of anti-CD40 antibodies showed reduced expression of both activation-induced cytidine deaminase (AID) and α germline transcripts (GLT) compared to controls. It was possible, however, to induce AID and α GLT when stimulating the cells with anti-CD40 antibody and TGF-β in the combination with IL-10. Moreover, in anti-CD40 antibody-stimulated cultures, addition of IL-10 or IL-10 + TGF-β in combination, induced IgA production, albeit lower than found in B cells from controls. The B cells from the IgA-deficient subjects were less effective in differentiating into CD138+ X-box binding protein 1 (XBP-1)+ plasma cells when stimulated with TGF-β, IFN-γ or IL-10. Interestingly, when adding IL-4 to TGF-β alone or in combination with IL-10, the immunoglobulin production in B cells from IgA-deficient donors was comparable with those of normal controls. These data show that in healthy subjects in vitro IgA production can be up-regulated by addition of IL-10 to CD40-stimulated B cells, whereas a similar B cell differentiation does not occur in IgA-deficient subjects. Addition of IL-4, however, reverts this abnormality.
Immunogenicity and protective efficacy of a recombinant filamentous haemagglutinin from Bordetella pertussis
Authors: Knight J B , Huang Y Y , Halperin S A , Anderson R , Morris A , MacMillan A , Jones T , Burt D S , Van Nest G , Lee S F
Published: April 2006

Bordetella pertussis is the causative agent of whooping cough, a major childhood pathogen; acellular vaccines consisting of purified B. pertussis antigens such as filamentous haemagglutinin (FHA) are commonly used to prevent pertussis. Despite the importance of FHA in B. pertussis pathogenesis and its inclusion in most acellular vaccines, the functional importance of individual domains in the induction of protective immunity is largely unknown. In this study, we have purified a recombinant FHA protein from Escherichia coli consisting of a 42 kDa maltose binding domain of E. coli and the 43 kDa type I immunodominant domain of FHA. The fusion protein (Mal85) was purified from E. coli cell lysates via affinity chromatography with an amylose column. Mal85 was then delivered to BALB/c mice intranasally encapsulated in liposomes, formulated with ProtollinTM or in conjuction with an immunostimulatory CpG oligonucleotide. Mice were also vaccinated intraperitoneally with alum-adsorbed Mal85. Sera from all treatment groups showed strong IgG responses to Mal85 and recognized native FHA. Specific salivary IgA was induced in mice vaccinated with Mal85 in liposomes, ProtollinTM and delivered with CpG. Vaccination with Mal85 encapsulated in liposomes or formulated with ProtollinTM provided protection against aerosol challenge with B. pertussis in BALB/c mice. These data indicate that the type I domain of FHA is a protective antigen in mice and may serve as a candidate for inclusion in new acellular pertussis vaccines.
Multiple suppression by 2D filtering in the parabolic τ–p domain: a wave‐equation‐based method1
Authors: Zhou Binzhong , Greenhalgh Stewart
Published: April 2006

The filter for wave‐equation‐based water‐layer multiple suppression, developed by the authors in the x‐t, the linear τ‐p, and the f‐k domains, is extended to the parabolic τ‐2 domain. The multiple reject areas are determined automatically by comparing the energy on traces of the multiple model (which are generated by a wave‐extrapolation method from the original data) and the original input data (multiples + primaries) in τ‐p space. The advantage of applying the data‐adaptive 2D demultiple filter in the parabolic τ‐p domain is that the waves are well separated in this domain. The numerical examples demonstrate the effectiveness of such a dereverberation procedure. Filtering of multiples in the parabolic τ‐p domain works on both the far‐offset and the near‐offset traces, while the filtering of multiples in the f‐k domain is effective only for the far‐offset traces.

Tests on a synthetic common‐shot‐point (CSP) gather show that the demultiple filter is relatively immune to slight errors in the water velocity and water depth which cause arrival time errors of the multiples in the multiple model traces of less than the time dimension (about one quarter of the wavelet length) of the energy summation window of the filter. The multiples in the predicted multiple model traces do not have to be exact replicas of the multiples in the input data, in both a wavelet‐shape and traveltime sense. The demultiple filter also works reasonably well for input data contaminated by up to 25% of random noise. A shallow water CSP seismic gather, acquired on the North West Shelf of Australia, demonstrates the effectiveness of the technique on real data.
Linearized elastic parameter sections1
Authors: Ursin Bjørn , Ekren Bjørn Olav , Tjåland Egil
Published: April 2006

Contrasts in elastic parameters can be estimated directly from seismic data using offset‐dependent information in the PP reflection coefficient. A linear approximation to the PP reflection coefficient including three coefficients is fitted to the data, and relative contrasts in various elastic parameters are obtained from linear combinations of the estimated coefficients. Linearized elastic parameter sections for the contrasts in P‐wave impedance, P‐wave velocity, density, plane‐wave modulus, and the change in bulk modulus and shear modulus normalized with the plane‐wave modulus are estimated. If the average P‐ to S‐wave velocity ratio is known, linearized parameter sections including the contrast in the average P‐ to S‐wave velocity ratio and a fluid factor section can be computed. Applied to synthetic data, visual comparison of the estimated and true elastic parameter sections agree qualitatively, and the results are confirmed by an analysis of the standard deviation of the estimated parameters. The parameter sections obtained by inversion of a shallow seismic anomaly in the Barents Sea are promising, but the reliability is uncertain because neither well data nor regional trends are available.
Ground radar simulation for archaeological applications1
Authors: Carcione José M.
Published: April 2006

This work presents a new modelling scheme for the simulation of electromagnetic radio waves, based on a full‐field simulator. Maxwell's equations are modified in order to include dielectric attenuation processes, such as bound‐ and free‐water relaxation, ice relaxation and the Maxwell–Wagner effect. The new equations are obtained by assuming a permittivity relaxation function represented by a generalized Zener model. The convolution integral introduced by the relaxation formulation is circumvented by defining new hidden field variables, each corresponding to a different dielectric relaxation. The equations are solved numerically by using the Fourier pseudospectral operator for computing the spatial derivatives and a new time‐splitting integration algorithm that circumvents the stiffness of the differential equations. The program is used to evaluate the georadar electromagnetic response of a Japanese burial site, in particular, a stone coffin‐like structure.
Papua New Guinea MT: looking where seismic is blind1
Authors: Hoversten G. Michael
Published: April 2006

Hydrocarbon exploration in the Papuan fold belt is made extremely difficult by mountainous terrain, equatorial jungle and thick karstified Miocene limestones at the surface. The high‐velocity karstified limestones at or near the surface often render the seismic technique useless for imaging the subsurface. In such areas magnetotellurics (MT) provides a valuable capability for mapping subsurface structure. The main structural interface which can be mapped with MT, due to the large electrical contrast, is the contact between the resistive Darai limestone and the underlying conductive sediments of the Ieru Formation. In some areas the base of the Darai can be mapped with reasonable accuracy by fitting 1D models to the observed MT data. However, in many cases where 2D and 3D effects are severe, 1D interpretations can yield dramatically incorrect results. Numerical and field data examples are presented which demonstrate the severity of the 1D errors and the improvements in accuracy which can be achieved using a 2D inverse solution.

Two MT lines over adjacent anticlines, both with well control and seismic data, are used to demonstrate the application of 1D and 2D inversions for structural models. In both cases the seismic data provide no aid in the interpretations. The example over the Hides anticline illustrates a situation where 1D inversion of either TE or TM mode provides essentially the same depth to base of Darai as 2D inversion of both TE and TM. Both models provide base Darai depth estimates which are within 10% of that measured in the well. The example over the Angore anticline illustrates the inadequacy of 1D inversion in structurally complex geology complicated by electrical statics. The TE mode fits a 1D Darai thickness of 800 metres while the TM mode fits a 1D Darai thickness of 3500 metres, bracketing the thickness of 2450 metres observed in the well. The final 2D inversion model provides a depth estimate of 2250 metres. Four MT lines along the Angore anticline have been interpreted using 2D inversion. A high degree of correlation exists between lineaments observed on an airborne radar image and zones of low resistivity within the high‐resistivity material interpreted as Darai limestone. These low‐resistivity zones are interpreted as fault zones.

Three‐dimensional modelling has been used to simulate 3D statics in an otherwise 2D earth. These data were used to test the Groom‐Bailey (GB) decomposition for possible benefits in reducing static effects and estimating geoelectric strike in the Papua New Guinea (PNG) field data. It has been found that the GB decomposition can provide improved regional 2D strike estimates in 3D contaminated data. However, in situations such as PNG, where the regional 2D strike is well established and hence can be fixed, the GB decomposition provides apparent resistivities identical to those simply rotated to strike.
Nursing in nosocomial infection control in Spain
Authors: Plitt‐Gómez Clemencia , Molina‐Quilis Rosa , Ruiz‐Bremón Ana , de Pedro‐Cuesta Jesús
Published: May 2006

This is a descriptive study of nursing practices in nosocomial infection control (NIC) in Spain During the period 1990‐1991, a questionnaire, adapted from that used in the Study on the Efficacy of Nosocomial Infection Control (SENIC), was mailed to all Spanish general hospitals, public and pnvate, having more than 400 beds, and to all those in the public health sector having more than 100 beds Nursing‐related information was selected for analysis from each of three sections staff, surveillance systems and programmes The response rate was 70% While nursing resources allocated to NIC in Spain registered an overall ratio of nosocomial infection control nurses (ICNs) of mean 0 45, SD 0 71 ICN per 250 hospital beds, ICN/beds ratios were below 0 34 and 0 30 in medium‐sized and large hospitals respectively Nurses who were active in NIC were either lacking or worked only a few hours per week in a considerable proportion of hospitals, with this trend being more pronounced in smaller facilities The intervening period since 1965, and the last decade in particular, has been marked by the progressive adoption of a range of NIC policies Most procedures proving NIC‐efficient had been implemented in approximately 70‐80% of responding hospitals Teaching was most qualified and intensive in medium‐sized hospitals Nursing in NIC has only recently been developed in Spain, is increasingly accepted, exhibits diffusion levels comparable to those reported internationally, lacks monitoring and quality assessment systems and, in general, could be substantially improved
A presentation of a conceptual framework and its use in the definition of nursing development within a number of nursing development units
Authors: Graham Lain
Published: May 2006

This paper provides a conceptual framework upon which action plans can be built to enable registered nurses to reflect upon their work and practice activities This conceptual framework has been used by the author in his work with various nursing development units within Yorkshire, England, in his role as their academic nurse advisor The framework has been useful in helping nurses not only to reflect upon current work and practice activities but also as a guideline for future development The paper provides examples of such nursing development activities and includes a personal view of how nursing development units can act as catalysts for change
Intraspecific genetic diversity of the endemic freshwater crab Candidiopotamon rathbunae (Decapoda, Brachyura, Potamidae) reflects five million years of the geological history of Taiwan
Authors: Shih Hsi‐Te , Hung Huei‐Chuan , Schubart Christoph D. , Chen Chaolun Allen , Chang Hsueh‐Wen
Published: April 2006

Aim  Candidiopotamon rathbunae (Crustacea: Brachyura: Potamidae) is a freshwater crab endemic to Taiwan, with a distribution covering almost the entire island. Crab populations from different river systems cannot be distinguished morphologically. In this study, we investigate the phylogeography of C. rathbunae from 18 of the main river systems of Taiwan, in order to reveal geographical differentiation and cryptic endemism. We used specimens of two congeners (C. okinawense and C. kumejimense) and the closely related Amamiku amamensis from the Ryukyu Islands as outgroups.

Location  Taiwan, with the Ryukyu Islands (Japan) as the outgroup locality.

Methods  Mitochondrial DNA sequences encoding 553 basepairs of the large subunit rRNA (16S rRNA) gene were obtained from 96 specimens throughout Taiwan and the Ryukyus. We compared these sequences by means of phylogenetic analyses (minimum evolution, maximum likelihood, maximum parsimony, and a genealogical parsimony network) and molecular‐clock time estimates.

Results  The estimated timing of the corresponding separations clearly correlates with geological events during the Penglai Orogeny of Taiwan (c. 5 Ma) following the collision of the Philippine Sea plate with the Eurasian continental plate. A deep split of 6.29% sequence divergence was found between the eastern clade (S, SE, and E groups) and the western clade (NW, W, and SW groups) of C. rathbunae. Separation of these groups reflects the isolating effect of the uplift of the Taiwan Central Range (c. 5 Ma). The separation of the SW group from the W group, and of the E group from the SE group can also be explained by geological events during the Taiwanese orogeny, the estimated geological timing being in close accordance with our molecular dating.

Main conclusions  According to the molecular results, the ancestral Candidiopotamon was among the earliest non‐marine colonizers of Taiwan, settling on this island no later than the early Pliocene. Our molecular data reveal that C. rathbunae can be subdivided into six groups in accordance with geography.
A new FtsZ‐interacting protein, YlmF, complements the activity of FtsA during progression of cell division in Bacillus subtilis
Authors: Ishikawa Shu , Kawai Yoshikazu , Hiramatsu Konosuke , Kuwano Masayoshi , Ogasawara Naotake
Published: May 2006

The assembly of ring‐like structures, composed of FtsZ proteins (i.e. the Z ring), is the earliest and most essential process in bacterial cytokinesis. It has been shown that this process is directly regulated by the FtsZ‐binding proteins, FtsA, ZapA, and EzrA, in Bacillus subtilis. In this study, protein complexes that are involved in Z‐ring formation were chemically cross‐linked in vivo, purified by affinity chromatography, and analysed by mass spectrometry. Analysis of the results identified YlmF as a new component of the FtsZ complex. Yeast two‐hybrid analysis and fluorescence microscopy of YFP–YlmF in B. subtilis cells indicated YlmF localizes to the division site in an FtsZ‐dependent manner. A single disruption of YlmF resulted in a slight elongation of cells; however, simultaneous inactivation of both YlmF and FtsA showed synthetic lethality caused by complete blockage of cell division due to the defect in Z‐ring formation. In contrast, the ftsA‐null mutant phenotype, caused by inefficient Z‐ring formation, could be complemented by overexpression of YlmF. These results suggest that YlmF has an overlapping function with FtsA in stimulating the formation of Z rings in B. subtilis.
Quaternary structure changes and kinetics of urease inactivation by L‐usnic acid in relation to the regulation of nutrient transfer between lichen symbionts
Authors: VICENTE C. , AZPIROZ A. , ESTÉVEZ M. P. , GONZÁLEZ M. L.
Published: April 2006

Abstract L‐usnic acid inactivates urease by the formation of high molecular weight aggregates which can reach a maximum of 700,000 under experimentation conditions previously described. The substrate, urea, itself provokes temporary aggregation states which may be either active or inactive; the latter being reversible. However, these inactive aggregates, of 820,000 molecular weight, are irreversibly stabilized by L‐usnic acid. The active aggregates with molecular weights oscillating from 605,000 to 650,000, depending on whether they are formed in the presence or absence of inactivator, may combine with the substrate to form an apparently normal ES complex.
The turbulent boundary layer over a flapping Populus leaf
Authors: GRACE J.
Published: April 2006

Abstract The air‐flow regime over a Populus leaf was investigated using a constant temperature hot‐film sensor which could be glued on the abaxial surface. The leaf was exposed to a laminar or turbulent flow of air in a wind‐tunnel, while being free to undergo normal motion. In the laminar air‐flow the boundary layer remained laminar, despite the fluttering of the leaf, until a Reynolds number of 2.3 × 104 was reached. When the air incident on the leaf was made turbulent, to resemble natural conditions, the boundary layer became turbulent at a Reynolds number of 0.4 × 104. The experiments suggest that the boundary layers over leaves are always turbulent in the natural wind.
Regulation of plant water potential by membranes of the endodermis in young roots
Authors: POWELL D. B. B.
Published: April 2006

Abstract The relationship between the flow of water through roots in young plants and the associated difference in water potential has often been found to be nonlinear. In this paper it is shown how the Casparian strip forces water, moving from the soil to the xylem of a young root, to pass through the cells of the endodermis, flushing solutes from them and reducing their turgor. It is suggested that the membranes of these cells like those of giant algal cells, respond to change in turgor by changing their hydraulic conductivity. These effects, when combined, are shown to produce a feedback system with a steady state behaviour which could account for some or all of the non‐linear relations, between rate of water uptake by young plants and differences between water potentials of the xylem and rooting medium, observed by workers such as Stoker & Weatherley (1971). Some non‐steady state responses of the system are explored, and it is suggested that the system also provides the link between the diurnal rhythms of solute concentration in the xylem sap, observed by Vaadia (1960), and of resistance to uptake of water by roots, reported by Parsons & Kramer (1974) amongst others.
Biometrical studies of plant growth
Authors: CAUSTON D. R. , ELIAS C. O. , HADLEY P.
Published: April 2006

Abstract Relevant mathematical properties of the Richards function are described, along with references to its employment in previous work, and a brief description is given of some of the difficulties encountered in its use. Two introductory experiments were undertaken: firstly, applying the Richards function to leaf growth of Impatiens parviflora DC; and secondly, applying the function to artificial sets of data of differing variability and differing spreads of observation‐values along the growth curve. The purpose of the latter analysis was an attempt to elucidate some problems of fitting and interpretation arising in the first experiment. It was concluded that the prime aim in experimental work generally is the acquisition of data covering as large a range of sizes as possible; low variability of the replicate observations, while desirable, is not so important. 

In another series of experiments, plants of Impatiens parviflora were grown at four different temperatures in the range 13–23°C inclusive. In terms of leaf dry weight, increase in temperature decreased the final size attained and increased the mean relative growth rate; the curvature of the growth curve and the mean absolute growth rate were, however, temperature independent. These results are brought together in a simple model which shows clearly how temperature affects the course of leaf dry weight increase in these plants. The results for leaf area are less clear, but both the mean absolute and relative growth rates increased with rise in temperature. The final area of a leaf and the curvature of the growth curve seemed to be little affected by temperatures in the range 16–23°C, but there was some evidence of differences in these features in leaves growing at 13°C. No model summary was attempted for leaf area increase.
C4 characteristics of photosynthesis in the C3 alga Hydrodictyon africanum
Authors: RAVEN J. A. , GLIDEWELL S. M.
Published: April 2006

Abstract Results obtained with Hydrodictyon africanum, and data from the literature, show that most green algae of the chlorophyte type (e.g. Chlorella, Chlamydomonas, Hydrodictyon) differ in their photosynthetic C fixation characteristics from most green algae of the charophyte type (e.g. Spirogyra, Chara) and from C3 higher plants. The chlorophyte algae fix inorganic carbon by the photosynthetic carbon reduction cycle pathway, but have a low CO2 compensation point in 250 μM O2, a low inhibition of CO2 fixation from 10 μM CO2/250 μM O2 when compared with 10 μM CO2/zero O2, and a low half‐saturation constant for CO2. These three characteristics are different from those of charophytes and C3 higher plants, and resemble those of C4 higher plants. It is suggested that these characteristics of chlorophyte algae are the result of a ‘CO2 concentrating mechanism’ which increases the CO2/O2 ratio at the site of ribulose bisphosphate carboxylase‐oxygenase action in a similar way to that achieved by the C4?C3 acid cycle in C4 plants. In the chlorophyte algae, however, CO2 concentration probably involves active HCO3− transport at the inner membrane of the chloroplast envelope. Active HCO3− transport can occur at the plasmalemma of charophyte algae and submerged aquatic higher plants as well as chlorophyte algae, so it is unlikely to explain the differences between the two groups of aquatic green plants. Differences in the properties of ribulose bisphosphate carboxylase‐oxygenase, and differences in CO2 production in the light, also seem inadequate to account for the different photosynthetic characteristics. The chlorophyte type of ‘C02 concentrating mechanism’ appears to be common in other classes of eukaryotic algae, and in cyanophytes. Some of the ‘advanced’ members of these eukaryotic algal classes (including the chlorophytes) may lack the mechanism, while some ‘primitive’ charophytes may retain the mechanism which their ancestors presumably possessed.
Citrus leaf abscission. Regulatory role of exogenous auxin and ethylene on peroxidases and endogenous growth substances
Authors: GASPAR T. , GOREN R. , HUBERMAN M. , DUBUCQ M.
Published: April 2006

Abstract The abscission of citrus leaf explants demonstrates the well‐known enhancing effect of ethylene and the delaying one of auxin when treatment is started at excision time. Total peroxidase activity increases differently in tissues of the blade, abscission zone, and petiole. The highest activity at zero time is recovered in abscission zone in which also the response to the abscission regulators is the most visible. Isoperoxidase profiles are modified in opposite directions by ethylene and auxin respectively. Both regulators affect the activity of the same cathodic and anodic isoperoxidases without any qualitative changes. By the same time, auxin‐like compounds increase in isolated abscission zones at 24 h from excision and decrease at 48 h. The level of one inhibitor complex undergoes an inverse variation.

It is suggested that the increase in auxin during the first stage of abscission is necessary for influencing the growth of cells which is required to cause abscission.
Radial electrogenic activity in the stem of Vigna sesquipedalis: involvement of spatially separate pumps
Authors: OKAMOTO HISASHl , ICHINO KAZUO , KATOU KIYOSHI
Published: April 2006

Abstract. The surface electric potential of Vigna sesquipedalis stem, relative to that of the root medium, was most negative in the elongating zone where the difference in pH between parenchyma (P) and xylem sap (X) was at a maximum. The surface electrical potential was found to be determined by the distribution of radial potential difference (Vsx comprised two components; Vsx=Vpx−Vps.There were two electromotive forces, generating Vps at the surface of the parenchyma symplast and Vpx between P and X; both were partially dependent on respiration. The depolarization of Vpx upon removal of O2 was maximal in the elongating zone, suggesting that the activity of an H+‐pump extruding protons from the parenchyma into the xylem in exchange for K+ was greatest in this zone.
The effect of low temperatures on the phloem transport of radioactive assimilates in the stolon of Saxifraga sarmentosa L.
Authors: CHAMBERLAIN IRENE S. , SPANNER D. C.
Published: April 2006

Abstract. The movement of naturally assimilated 14C down the stolon of Saxifraga sarmentosa under the influence of localized cold treatments (0°‐10°C) applied over lengths up to 10 cm was followed by finding the distribution of tracer at the termination of the experiment. Inhibition is slight at 10°C and very considerable at 0°C. It is very dependent on the length treated, but is definite even when this is only 0.8 cm. Cooling the daughter plantlet to 0°C has a smaller inhibitory effect than might be expected. This is difficult to understand if ‘unloading’ is metabolic; perhaps the concentration free energy of the sucrose or other solute can be utilized in the sink terminals on the lines of the chemi‐osmotic hypothesis. If so the same source of non‐respiratory free energy might be available to energize an active sieve‐tube mechanism in mid‐path chilling experiments.
Cd uptake by intact wheat plants
Authors: SMEYERS‐VERBEKE J. , DE GRAEVE M. , FRANCOIS M. , DE JAEGEREf R. , MASSART D. L.
Published: April 2006

Abstract. An investigation of the uptake of Cd by intact wheat plants has been carried out. The accumulation of Cd in the roots as a function of time and external Cd concentration was determined. Since the transport of Cd to the grains and shoots was found to be small, only uptake into the root was examined further. An appreciable fraction of the Cd absorbed by the roots can be desorbed and consequently constitutes the freely diffusible and exchangeable fraction.

The effect of temperature and of metabolic inhibitors on the absorption provides evidence that another Cd fraction is taken up by metabolically mediated processes. The absorption of this Cd fraction was found to be inhibited by Cu and Zn. The inhibitory effect of Cu and Zn on Cd absorption was comparable.
Transport of purines and pyrimidines into isolated pea chloroplasts
Authors: BARBER D. J. , THURMAN D. A.
Published: April 2006

Abstract. Uptake of [14C] adenine and [14C] cytosine into isolated pea chloroplasts has been examined by using a centrifugal‐filtration technique. These chloroplasts accumulate both compounds in the sucrose‐impermeable space to concentrations higher than that present in the external solution when the latter was below 1.0 mM. Competition experiments suggested that uptake is mediated by a carrier mechanism.
An inhibitory effect of excess moisture on the early development of Sinapis alba L. seedlings
Authors: MACDONALD I. R. , GORDON D. C.
Published: April 2006

Abstract. Mustard seedlings in the early stages of growth are sensitive to the presence of excess moisture, growth of the radicle and anthocyanin synthesis being retarded by water at a suction of less than 3 cm water for seedlings growing on a plane surface. This inhibitory effect commences at about 12‐15 h from wetting of the seed. It can be counteracted by increasing the partial pressure of oxygen in the atmosphere or by de‐coating the seed, suggesting that the inhibition is caused by a restricted flow of oxygen through the mucilaginous seed coat. The positive effect of gravity on anthocyanin synthesis in the developing seedling can be wholly accounted for in terms of the removal of excess moisture. This explanation largely accounts for the improved growth of the root, but a tonic effect of gravity on root growth can also be discerned.
Characterization of fusicoccin binding to receptor sites on cell membranes of maize coleoptile tissues
Authors: PESCI P. , COCUCCI S.M. , RANDAZZO G.
Published: April 2006

Abstract Radioactive dihydrofusicoccin (3H‐FC), known to have the same biological activity as fusicoccin on plant tissues, has a specific affinity in vitro for sites localized on subcellular, postmitochondrial particles from maize coleoptiles. The analysis of the kinetics of dihydrofusicoccin binding suggests the presence of two classes of sites, one class with a high affinity and a second class with a lower affinity. The high affinity class of sites has a dissociation constant (Kd) of 1.2 × 10−9 mol dm−3, and an apparent pH optimum at 5.5. Binding is antagonized by non‐physiological pH, high temperatures and protein‐reactive substances like HgCl2, p‐chloromercuribenzensulphonate and glutaraldehyde. Treatment of dihydrofusicoccin‐bound membrane preparations with Triton X‐100 leads to the solubilization of a protein fraction associated with dihydrofusicoccin. These data suggest a protein nature for the receptor sites.
A light and electron microscopy study of the epidermis of Paphiopedilum spp. with emphasis on stomatal ultrastructure
Authors: RUTTER J. C. , WILLMER C. M.
Published: April 2006

Abstract Light and fluorescence microscopy studies indicated that chlorophyll was absent from the guard cells of the lady slipper orchids, Paphiopedilum insigne (Wall.) Pfitz, P. insigne (hybrid), P. venustum (Wall.) Pfitz and P. harrisseanum Hort. In the guard cells of P. aureum hyeanum Hort., however, very slight red fluorescence suggested that chlorophyll and hence chloroplasts were present.

Ultrastructural studies of the lower epidermis of P. insigne (hybrid) confirmed the absence of chloroplasts in guard and epidermal cells although plastids of an unusual structure were found in these cells. In fully developed epidermal cells the plastids contained large amounts of a fibrous, possibly proteinaceous substance, spherical, lightly staining vesicles and an electron‐dense material located in reticulate and non‐reticulate regions. Additionally, latticed crystalline inclusions and plasto‐globuli were occasionally observed in the epidermal cell plastids. In plastids of fully developed guard cells the fibrous material, starch and plastoglobuli were present.

From the earliest stages of development of the epidermal tissue starch was present in both epidermal cell and guard cell plastids. At maturity, however, starch had accumulated to greater levels in the guard cell plastids and had entirely disappeared in the epidermal cell plastids. In differentiating epidermal tissue, plasmodesmata were found between neighbouring epidermal cells and between guard and epidermal cells. At maturity, plasmodesmata between guard and epidermal cells were not observed. Mitochondria were particularly abundant in guard cells. Large oil drops developed in guard and epidermal cells, being especially abundant in the former at maturity.

Our results confirm the observations of Nelson & Mayo (1975) that certain lady slipper orchids possess functional stomata the guard cells of which do not contain chloroplasts.
An enzymic microassay for starch
Authors: JONES M. G. K.
Published: April 2006

Abstract Conditions are described for measuring the starch content of plant tissues or extracts as glucose over the range from 10−7 mol to 10−14 mol. The method is based on the hydrolysis of gelatinized starch by amyloglucosidase; the glucose released is measured by reduction of NADP+ by coupled enzymic reactions.

The NADPH is determined directly either spectrophotometrically or fluorimetrically, or after enzymic amplification. Amyloglucosidases were tested for contaminating enzymes which might degrade glucans other than starch, and a commercial preparation from Rhizopus niveus was found to be suitable for use without pretreatments. Glucose present in tissues and extracts may be measured and subtracted from starch values using appropriate blanks, or first destroyed by dilute alkali and heat. Addition of α‐amylase to amyloglucosidase during starch hydrolysis was not found to increase percentage hydrolysis from the normal range of 86–99% from starches of different sources.

The procedures described are rapid and several orders of magnitude more sensitive than current methods, and can be used to measure the starch content of single cells.
Photodynamic activity of cercosporin on plant tissues
Authors: MACRÍ F. , VIANELLO A.
Published: April 2006

Abstract Cercosporin, excited by incandescent light in the presence of oxygen, induced a loss of ions from the plant tissues tested. Silymarin, BHA (2(3)‐tert‐butyl‐4‐hydroxyanisole) and EDTA were effective in lowering the activity of cercosporin. Circumstantial evidence suggests that the toxic effect may be mediated by the singlet oxygen and free radical formation which induces a lipoperoxidative degradation of the polyunsaturated fatty acids of cell membranes.
Post‐secretory determinants of sugar concentration in nectar
Authors: CORBET SARAH A. , WILLMER P. G. , BEAMENT J. W. L. , UNWIN D. M. , PRŶS‐JONES O. E.
Published: April 2006

Abstract. The concentration of sugar in the nectars of unprotected flowers of several species was measured and did not reach the high values that would be in equilibrium with the daytime humidities recorded outside the corolla, although the sugar concentration was highly correlated with ambient relative humidity. This paper examines features that maintain low nectar sugar concentrations at low ambient humidities. Post‐secretory changes in concentration are influenced to a small extent by nectar composition but depend largely on physico‐chemical and microclimatic effects. Factors contributing to the maintenance of steep gradients in water activity between the nectar and the ambient air include corolla morphology, sugar concentration gradients and waterproofing lipid monolayers on the nectar surface. This paper considers the relative importance of such features in relation to the pollination syndrome. A simple technique is described for the measurement of intrafloral relative humidity.