Plasmids for recombination-based screening.

To facilitate recombination-based screening, we constructed the ColE1-based plasmid, pi G4, that confers chloramphenicol resistance, contains a polylinker with multiple unique restriction enzyme recognition sequences, and contains the genetic marker, supF. To facilitate recombination-based screening followed by rapid DNA sequencing, we inserted the selectable marker, supF, into each of 20 high-copy-number (hcn) pUC-derived NoC plasmids that were designed for multiplex DNA sequencing. To facilitate recombination-based screening of common cDNA libraries that often contain ColE1 sequences, we constructed a supF-carrying plasmid whose replication was driven from an R6K replicon that does not share sequence homology with ColE1. Furthermore, we incorporated a useful polylinker and increased the copy number of this plasmid to create the 4.4-kb hcn plasmid, pMAD1. Thus, these plasmids allow: (1) background-free transformation of cells by a supF plasmid carrying an antibiotic-resistance marker; (2) simultaneous performance of the recombination-based assay and DNA sequencing; and (3) screening bacteriophage cDNA libraries that contain ColE1 sequences by recombination with a supF plasmid that is not homologous to ColE1 derivatives.     

Approaches to understanding the functional architecture of the plant cell wall.

Cell wall polysaccharides are some of the most complex biopolymers known, and yet their functions remain largely mysterious. Advances in imaging methods permit direct visualisation of the molecular architecture of cell walls and the modifications that occur to polymers during growth and development. To address the structural and functional relationships of individual cell wall components, we need to better characterise a broad range of structural and architectural alterations in cell walls, appearing as a consequence of developmental regulation, environmental adaptation or genetic modification. We have developed a rapid method to screen large numbers of plants for a broad range of cell wall phenotypes using Fourier transform infrared microspectroscopy and Principal Component Analysis. We are using model systems to uncover the genes that encode some of the cell-wall-related biosynthetic and hydrolytic enzymes, and structural proteins.     

Valuation study of urban bushland at Hartfield Park, Forrestfield, Western Australia

Summary Hartfield Park bushland represents a typical area of Perth urban bushland, and is identified as one site worthy of protection in the Western Australian Government's Bush Forever Plan. Two thirds of the Reserve is developed and parts of the remaining bushland are under threat of future development for parking and playing fields. This paper reports a study undertaken to estimate the economic value placed by the community on a specified urban bushland site using the contingent valuation method, a stated preference, non‐market valuation technique which captures both use and non‐use values. Because environmental goods such as urban bushland exist without organized markets, they are often omitted from the decision‐making process regarding the socially optimal management of resources. In estimating a valuation for Hartfield Park, it may be included in any cost–benefit analysis conducted for the site in future. A survey was conducted across the Perth metropolitan area during April 2001 that involved the mail out of 1000 questionnaires to names and addresses obtained at random from the Western Australia Electoral Roll. A 54% response rate was obtained. Regression analysis was used to predict the probability of people being willing to pay for the preservation of this urban bushland and the significant predictors of willingness to pay related to income and educational levels rather than proximity to or knowledge of the site. Willingness to pay was also estimated and the results indicate a conservative mean willingness to pay for the preservation of the bushland of $A21.60 per person per annum. Extrapolation of this figure across the total adult metropolitan community resulted in an estimated valuation of $A16.6 million. Median willingness to pay was also estimated and equalled $A4.35 per person per annum with a valuation for the total adult metropolitan community equal to $A3.3 million. Extrapolation of these mean and median figures across Perth households rather than adult individuals resulted in an estimated valuation of $A9.6 million and $A1.9 million, respectively. These figures indicate that the community value for this environmental amenity may exceed the costs of providing alternative facilities elsewhere.     

Simple rules for the coexistence and competitive dominance of plants mediated by mycorrhizal fungi

Mycorrhizal fungi have been demonstrated to be important in the makeup of plant communities. Likely, their most important role is in altering mineral nutrition of plants, which, in turn, is thought to be among the most important determinants of plant competitive ability. Using mathematical models we examine what role these fungi can play in determining the competitive outcome between two plants in competition for one mineral resource. Depending on different relationships between the benefit accrued to the plant and the fungi, the presence of mycorrhizal fungi can (i) have no impact on which plant wins in competition, (ii) change the order of competitive dominance or (iii) enable coexistence when compared with the system in the absence of mycorrhizal fungi. Furthermore, environmental conditions, such as light and nutrient levels, can determine if coexistence is possible. We describe the necessary biological trade‐offs for coexistence and experimental tests for these trade‐offs.     

Size reduction associated with brachymesophalangia-5: a possible selective advantage

The skin reflectance characteristics of a group of Quechua Indians have been described with an emphasis upon the effects of varying degrees of hybridization, sex and age. This group of Peruvian Indians occupied a reflectance range common to that of all other reported groups of South American Indians. Miscegenation with European Whites had a statistically significant although small influence upon skin color. In general males were consistently darker than females on the three body sites measured. A significant darkening on unexposed body areas occurred in both sexes during early adolescence which may have been caused by the high activity level of the pituitary gland at that stage of the growth cycle.     

Computer-aided Diagnosis: Description of an Adaptable System,and Operational Experience with 2,034 Cases

This paper describes a system of computer-aided diagnosis using an English Electric KDF9 computer linked to a terminal in a busy clinical department. Data from a series of patients were recorded, coded, and entered into the computer, which then performed a Bayesian analysis and displayed diagnostic probabilities in an adaptable format. Experience in this setting suggests that computer diagnosis may be a valuable aid to the clinician.     

Development and application of white-noise modeling techniques for studies of insect visual nervous system

The nonlinear system identification technique through white-noise stimulation is extended to multi-input, -output systems with consideration given to applications in the functional study of the nervous system. The applicability of the method is discussed in general and in particular for the motion detection neuronal system of the fly. Two series of experiments are performed; one with moving striped-pattern stimuli and the other with spot stimuli of fluctuating intensity. In both cases nonlinear dynamic models are derived which describe the system with considerable accuracy over the frequency range of 0.2–50 Hz and a dynamic amplitude range of about 40-1. These models are able to predict accurately all the discrete experiments so far performed on this system for which the models are applicable. The differences in dynamic characteristics between the corresponding system of the Musca and Phoenicia families of flies are minor except for a difference in latencies and if the difference in geometry of their faceted eyes is taken into account. The large field response of the motion detection unit is a linear weighted summation of all the smaller field highly nonlinear subsystems of which the large field is comprised.     

Reconstitution of oxidative phosphorylation and the adenosine triphosphate-dependent transhydrogenase activity by a combination of membrane fractions from uncA? and uncB? mutant strains of Escherichia coli K12

1. Membrane preparations from both uncA(-) and uncB(-) mutant strains of Escherichia coli K12, in which electron transport is uncoupled from phosphorylation, were fractionated by washing with a low-ionic-strength buffer. The fractionation gave a ;5mm-Tris wash' and a ;membrane residue' from each strain. This technique, applied to membranes from normal cells, separates the Mg(2+),Ca(2+)-stimulated adenosine triphosphatase activity from the membrane-bound electron-transport chain and the non-energy-linked transhydrogenase activity. 2. Reconstitution of both oxidative phosphorylation and the ATP-dependent transhydrogenase activity was obtained by a combination of the ;membrane residue' from strain AN249 (uncA(-)) with the ;5mm-Tris wash' from strain AN283 (uncB(-)). 3. Valinomycin plus NH(4) (+) inhibited oxidative phosphorylation both in membranes from a normal strain of E. coli and in the reconstituted membrane system derived from the mutant strains. 4. The electron-transport-dependent transhydrogenase activity was located in the membrane residue and was de-repressed in both the mutant strains. 5. The spatial and functional relationships between the proteins specified by the uncA and uncB genes and the transhydrogenase protein are discussed.     

Maize Brittle Stalk2-Like3, encoding a COBRA protein,functions in cell wall formation and carbohydrate partitioning

Carbohydrate partitioning from leaves to sink tissues is essential for plant growth and development. The maize (Zea mays) recessive carbohydrate partitioning defective28 (cpd28) and cpd47 mutants exhibit leaf chlorosis and accumulation of starch and soluble sugars. Transport studies with ¹⁴C-sucrose (Suc) found drastically decreased export from mature leaves in cpd28 and cpd47 mutants relative to wild-type siblings. Consistent with decreased Suc export, cpd28 mutants exhibited decreased phloem pressure in mature leaves, and altered phloem cell wall ultrastructure in immature and mature leaves. We identified the causative mutations in the Brittle Stalk2-Like3 (Bk2L3) gene, a member of the COBRA family, which is involved in cell wall development across angiosperms. None of the previously characterized COBRA genes are reported to affect carbohydrate export. Consistent with other characterized COBRA members, the BK2L3 protein localized to the plasma membrane, and the mutants condition a dwarf phenotype in dark-grown shoots and primary roots, as well as the loss of anisotropic cell elongation in the root elongation zone. Likewise, both mutants exhibit a significant cellulose deficiency in mature leaves. Therefore, Bk2L3 functions in tissue growth and cell wall development, and this work elucidates a unique connection between cellulose deposition in the phloem and whole-plant carbohydrate partitioning.

Mutations in Bk2L3 result in dwarfed plants with decreased anisotropic cell growth, cellulose deposition, phloem pressure, sucrose export, and carbohydrate hyperaccumulation in mature maize leaves.