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.     

Observations and tracking of killer whales (Orcinus orca) with shore‐based X‐band marine radar at a marine energy test site

The Atlantic killer whale (Orcinus orca) is a top‐level marine predator with a global range, being found in all of Earth's oceans. The potential interaction between killer whales and marine renewable energy projects requires surveillance and monitoring efforts that call for new technologies, with marine radar showing promise in the field. Marine radar images recorded at the European Marine Energy Centre (EMEC) were used to track a pair of male killer whales undertaking Surface Active Behavior (SAB) with visual observations used as validation. Using a tidal prediction model, the tide‐adjusted, radar‐derived target speeds between SAB events provide estimates of swim speeds averaging 4 m/s and time between SAB events of 30 s. The similarities between the radar signatures of the animals and sea clutter, combined with their low occurrence compared to other imaged phenomena renders automatic detection with this system difficult. However, the combination of opportunistic radar imagery and independent visual observation has allowed the radar signature of one form of killer whale SAB to be documented. It is hoped that with a greater number of validated observations such as these that automated, radar‐based identification and the benefits it will bring to long‐term observations at MRE sites will be possible.     

A genome-based analysis of amino acid metabolism in the biotrophic plant pathogen Ustilago maydis

Amino acid, nitrogen and sulfur metabolism play critical roles in the growth and development of fungal pathogens both in and outside of the host. The genome sequence of Ustilago maydis provides an opportunity for exploring these biochemical pathways by comparison to known gene sequences from other fungi. This approach was used to identify candidate genes for almost all enzymes required for amino acid biosynthesis and degradation, as well as the uptake and assimilation of nitrogen and sulfur. A number of differences were found between U. maydis and other basidiomycetes, and between basidiomycetes and ascomycetes in general. The use of genomics to explore central metabolic pathways may be of value in characterizing strict biotrophic pathogens like U. maydis that seem to derive a very limited set of nutrients from the host and thus must retain extensive biosynthetic capacity.