A Model for the Development of the Rhizobial and Arbuscular Mycorrhizal Symbioses in Legumes and Its Use to Understand the Roles of Ethylene in the Establishment of these two Symbioses

We propose a model depicting the development of nodulation and arbuscular mycorrhizae. Both processes are dissected into many steps, using Pisum sativum L. nodulation mutants as a guideline. For nodulation, we distinguish two main developmental programs, one epidermal and one cortical. Whereas Nod factors alone affect the cortical program, bacteria are required to trigger the epidermal events. We propose that the two programs of the rhizobial symbiosis evolved separately and that, over time, they came to function together. The distinction between these two programs does not exist for arbuscular mycorrhizae development despite events occurring in both root tissues. Mutations that affect both symbioses are restricted to the epidermal program. We propose here sites of action and potential roles for ethylene during the formation of the two symbioses with a specific hypothesis for nodule organogenesis. Assuming the epidermis does not make ethylene, the microsymbionts probably first encounter a regulatory level of ethylene at the epidermis–outermost cortical cell layer interface. Depending on the hormone concentrations there, infection will either progress or be blocked. In the former case, ethylene affects the cortex cytoskeleton, allowing reorganization that facilitates infection; in the latter case, ethylene acts on several enzymes that interfere with infection thread growth, causing it to abort. Throughout this review, the difficulty of generalizing the roles of ethylene is emphasized and numerous examples are given to demonstrate the diversity that exists in plants

On the relative importance of queens and workers to honey production

Colonies of honey bees (Apis mellifera) with different queen genotypes, but identical worker genotype, were established. The 2 groups differed significantly in both weight gain and brood area, indicating that queen genotype influences honey production. In a second experiment, 2 groups of genetically similar queens were inseminated with genetically dissimilar semen. The sire groups did not differ significantly in their honey production over a period of 3 months. It is concluded that queen genotype plays a significant part in colony genotypic merit for honey production, and that selection schemes which do not evaluate queen performance are likely to be only partially successful

Hydrophobic/hydrophilic effects on the titanium(IV)-catalyzed epoxidation of cyclohexene by tert-alkyl hydroperoxides: 2-methyl-l-phenyl-2-propyl hydroperoxide (MPPH) versus tert-butyl hydroperoxide (TBHP)

The epoxidation of cyclohexene in acetonitrile under argon at room temperature on a titanium(IV)-containing MCM41 silica catalyst is faster and gives a greater final yield of cyclohexene oxide when the oxygen atom donor is 2-methyl-l-phenyl-2-propyl hydroperoxide (MPPH) than when it is tert-butyl hydroperoxide. This is shown to be due to stronger retardation of the oxidation by tert-butyl alcohol (TBA) than by the alcohol derived from MPPH. The difference in retardation between these two alcohols is attributed to the greater hydrophilicity of TBA. Acetonitrile is a better solvent for this reaction than isooctane, pyridine and a variety of alcohols. These solvent effects are attributed to the hydrophilic nature of the catalyst.Peer reviewed: YesNRC publication: Ye

Evolutionary swarm robotics: genetic diversity, task-allocation and task-switching

The goal of this study is to investigate the role of genetic diversity for engineering more resilient evolutionary swarm robotic systems. The resilience of the swarm is evaluated with respect to the capability of the system to re-distribute agents to tasks in response to changes in operating conditions. We compare the performances of two evolutionary approaches: the clonal approach in which the teams are genetically homogeneous, and the aclonal approach in which the teams are genetically heterogeneous. We show that the aclonal approach outperforms the clonal approach for the design of robot teams engaged in two task-allocation scenarios, and that heterogeneous teams tend to rely on less plastic strategies. The significance of this study for evolutionary swarm robotics is discussed and directions for future work are indicated

Lipid peroxidation during myocardial ischaemia induced by pacing.

Oxygen derived free radical generation can be shown in experimental models of myocardial ischaemia and reperfusion and may cause cellular damage by peroxidizing polyunsaturated membrane phospholipids. An attempt was made to quantify human intracardiac lipid peroxidation during transient myocardial ischaemia by measuring the aortic and coronary sinus concentrations of malondialdehyde (a marker of lipid peroxidation) before, during, and after incremental pacing. Twenty six patients were paced until they had severe chest pain or 2 mm ST segment depression or they reached a paced rate of 180 beats/min. They were divided into two groups according to whether or not lactate was produced during pacing. Twelve patients (group 1), all with coronary artery disease, produced myocardial lactate during pacing. None of the other 14 patients (group 2), half of whom had coronary disease, produced lactate during pacing. Concentrations of malondialdehyde in the aorta and coronary sinus were significantly higher in group 1 than in group 2. Five minutes after the end of pacing coronary sinus malondialdehyde concentrations in group 1 had increased significantly from baseline values. There were no changes with time in the coronary sinus concentration of malondialdehyde in group 2 or in the aorta in either group. The negative malondialdehyde extraction ratio in group 1 suggests that intracardiac lipid peroxidation occurs during transient human myocardial ischaemia

Influence of weather conditions on fly abundance and its implications for transmission of Rabbit Haemorrhagic Disease Virus in the North Island of New Zealand

Blowflies (Diptera: Calliphoridae) and flesh flies (Diptera: Sarcophagidae) are potential vectors of rabbit haemorrhagic disease virus (RHDV) in New Zealand. The associations between habitat and weather factors on the abundance of these flies were investigated. Between October 1999 and June 2001, flies were trapped on open pasture and in dense vegetation patches on farmland in the Himatangi area of the North Island. Five calliphorid species were trapped commonly at scrub edges and the most abundant sarcophagid, Oxysarcodexia varia Walker, was trapped mainly on open pasture. An abundance peak of O. varia was probably associated with the occurrence of a rabbit haemorrhagic disease (RHD) outbreak in the study area. Overall abundance of flies varied according to habitat and species, and species numbers differed between seasons and years. The all-day minimum temperature 3 weeks before trapping was a significant variable in all models of fly abundance, whereas average rainfall did not affect fly abundance. The all-day temperature range was significant only for O. varia. The influence of other climatic factors varied between fly species. Climate dependent variations in fly abundance may contribute to the risk of transmission of RHD, which occurred intermittently on the site during the study period