Production of ethylene by gravistimulation: a potential problem with the interpretation of data from some experimental techniques

Abstract. Gravistimulation was investigated as a potential and unwanted component in the interpretation of physiological investigations on plants. Using both seedlings and mature sunflower plants, two situations are described where gravistimulation contributes significantly to the outcome of an experiment not initially designed to include this parameter. The number of adventitious roots formed in derooted seedings decreased when the tops of the plants were allowed to bend over under their own weight, and the effect correlated positively with the rate of ethylene production by non-vertical stems. In droughted mature plants, and increase in leaf and stem ethylene caused by water stress was supplemented by additional ethylene produced in the lower halves of stems. Drought had caused these stem tissues to wilt, become gravistimulated, and thus produce more ethylene. Other situations in which gravistimulated ethylene production and its physiological consequences are likely to be complicating factors in experiments are discussed. It is concluded that procedures that unnecessarily place experimental material in non-vertical orientations should be avoided.     

Block of Conduction in Partially Depolarized Cardiac Purkinje Fibres induced by an α-Adrenergic Agent

IF discrete areas of the ventricular conducting system are exposed to high concentrations of K⁺, conduction through these areas is slowed so much that the impulse may re-enter the normal part of the conducting system after the end of the refractory period, thereby evoking another excitation of the heart (refs. 1 and 2 and our unpublished work). This slow conduction results from a slow response that resembles the slow component of the cardiac action potential³ and the action potential of normal fibres of the atrioventricular node⁴. Adrenaline enhances the response of Purkinje fibres, depressed by exposure to high K⁺ concentration⁵ and we now report that an α-adrenergic agent, methoxamine, depresses the slow response at concentrations that do not affect the normal action potential. This finding is of interest because very few of the actions of adrenergic agents on the heart can be attributed to the stimulation of α-receptors⁶, because selective depression of the slow response is further evidence that it differs qualitatively from the response of normal fibres (our unpublished work) and because it suggests that α-adrenergic agents may be useful in the prevention of certain cardiac arrhythmias.     

Are environmental conditions recorded by the organic matrices associated with precipitated calcium carbonate in cyanobacterial microbialites?

The amino acid composition of organic matrices associated with calcium carbonate precipitates in microbialites built by different Phormidium species (cyanobacteria) has been compared for samples recovered in lagoonal settings from two regions of the Southern Tropical Pacific separated by more than 4000 km: New Caledonia (Nouméa lagoon) and French Polynesia (Tikehau atoll). Calcium carbonate precipitation in these microbial structures was observed mainly in the interior of the domes and clearly separated from the photosynthetically active surface layer. This study focuses on the hydrolysable amino acid composition of the associated organic matrices that are typically rich in cysteine, leucine, alanine and arginine in New Caledonia, whereas they are particularly rich in dicarboxylic amino acids in French Polynesia. This striking difference is seemingly related to different environmental conditions that characterize the two reef settings. The high cysteine content suggests an origin from metallothioneins produced by the cyanobacteria and/or by epiphytic diatoms that were observed on the top layer, as the result of the input of metals from terrestrial origin in the Nouméa lagoon. In addition, we analysed the bulk organic matter of the photosynthetically active surface layer and of the interior of the domes. The former showed remarkable variations of amino acid composition throughout the year 2001, which may potentially reflect the impact of climatological events (e.g. cyclones) and/or a much stronger seasonality in New Caledonia than in French Polynesia. Although the mechanisms behind the differences remain elusive, our study clearly shows that environmental conditions can be reflected by amino acid compositions, particularly for the organic matrices associated with carbonate precipitates.     

Intercomparison, interpretation, and assessment of spring phenology in North America estimated from remote sensing for 1982–2006

Shifts in the timing of spring phenology are a central feature of global change research. Long‐term observations of plant phenology have been used to track vegetation responses to climate variability but are often limited to particular species and locations and may not represent synoptic patterns. Satellite remote sensing is instead used for continental to global monitoring. Although numerous methods exist to extract phenological timing, in particular start‐of‐spring (SOS), from time series of reflectance data, a comprehensive intercomparison and interpretation of SOS methods has not been conducted. Here, we assess 10 SOS methods for North America between 1982 and 2006. The techniques include consistent inputs from the 8 km Global Inventory Modeling and Mapping Studies Advanced Very High Resolution Radiometer NDVIg dataset, independent data for snow cover, soil thaw, lake ice dynamics, spring streamflow timing, over 16 000 individual measurements of ground‐based phenology, and two temperature‐driven models of spring phenology. Compared with an ensemble of the 10 SOS methods, we found that individual methods differed in average day‐of‐year estimates by ±60 days and in standard deviation by ±20 days. The ability of the satellite methods to retrieve SOS estimates was highest in northern latitudes and lowest in arid, tropical, and Mediterranean ecoregions. The ordinal rank of SOS methods varied geographically, as did the relationships between SOS estimates and the cryospheric/hydrologic metrics. Compared with ground observations, SOS estimates were more related to the first leaf and first flowers expanding phenological stages. We found no evidence for time trends in spring arrival from ground‐ or model‐based data; using an ensemble estimate from two methods that were more closely related to ground observations than other methods, SOS trends could be detected for only 12% of North America and were divided between trends towards both earlier and later spring.     

Fungal effector proteins: past, present and future

The pioneering research of Harold Flor on flax and the flax rust fungus culminated in his gene-for-gene hypothesis. It took nearly 50 years before the first fungal avirulence ( Avr ) gene in support of his hypothesis was cloned. Initially, fungal Avr genes were identified by reverse genetics and map-based cloning from model organisms, but, currently, the availability of many sequenced fungal genomes allows their cloning from additional fungi by a combination of comparative and functional genomics. It is believed that most Avr genes encode effectors that facilitate virulence by suppressing pathogen-associated molecular pattern-triggered immunity and induce effector-triggered immunity in plants containing cognate resistance proteins. In resistant plants, effectors are directly or indirectly recognized by cognate resistance proteins that reside either on the plasma membrane or inside the plant cell. Indirect recognition of an effector (also known as the guard model) implies that the virulence target of an effector in the host (the guardee) is guarded by the resistance protein (the guard) that senses manipulation of the guardee, leading to activation of effector-triggered immunity. In this article, we review the literature on fungal effectors and some pathogen-associated molecular patterns, including those of some fungi for which no gene-for-gene relationship has been established.     

Survival of Herring Gull Larus argentatus chicks: an experimental analysis of the need for early breeding

In 1985 and 1990, we manipulated the hatching date of Herring Gulls Larus argentatus by exchanging complete clutches between pairs which had started egg laying on different dates in the season. The aim was to investigate whether the observed seasonal decline in Hedging success can be explained by laying date. In both years, fledging success of advanced pairs followed the natural seasonal trend, supporting the date hypothesis. However, in both years, Hedging success of delayed pairs remained as high as that of control pairs with the same original hatching date as the foster parents, supporting the parental quality hypothesis. These data suggest that the delayed pairs may have compensated for less favourable environmental conditions. Although conspecific predation was the main direct cause of chick mortality, food shortage probably indirectly determined the mortality rate. A model of fledging success in relation to the timing of egg laying predicts that when food is abundant the optimal hatching date coincides with the mean hatching date of the colony (synchronization advantage). When food is less abundant, early breeders have the highest fledging success.     

Cladosporium fulvum (syn. Passalora fulva), a highly specialized plant pathogen as a model for functional studies on plant pathogenic Mycosphaerellaceae

Taxonomy:  Cladosporium fulvum is an asexual fungus for which no sexual stage is currently known. Molecular data, however, support C. fulvum as a member of the Mycosphaerellaceae, clustering with other taxa having Mycosphaerella teleomorphs . C. fulvum has recently been placed in the anamorph genus Passalora as P. fulva . Its taxonomic disposition is supported by its DNA phylogeny, as well as the distinct scars on its conidial hila, which are typical of Passalora , and unlike Cladosporium s.s. , which has teleomorphs that reside in Davidiella , and not Mycosphaerella .
Host range and disease symptoms:  The presently known sole host of C. fulvum is tomato (members of the genus Lycopersicon ). C. fulvum is mainly a foliar pathogen. Disease symptoms are most obvious on the abaxial side of the leaf and include patches of white mould that turn brown upon sporulation. Due to stomatal clogging, curling of leaves and wilting can occur, leading to defoliation.
C. fulvum as a model pathogen:  The interaction between C. fulvum and tomato is governed by a gene-for-gene relationship. A total of eight Avr and Ecp genes, and for four of these also the corresponding plant Cf genes, have been cloned. Obtaining conclusive evidence for gene-for-gene relationships is complicated by the poor availability of genetic tools for most Mycosphaerellaceae – plant interactions. Newly developed tools, including Agrobacterium -mediated transformation and RNAi, added to the genome sequence of its host tomato, which will be available within a few years, render C. fulvum attractive as a model species for plant pathogenic Mycosphaerellaceae.
Useful websites:  http://www.sgn.cornell.edu/help/about/index.html ; http://cogeme.ex.ac.uk