Gastrulation: Is It Analogous to Malignant Invasion

The process of gastrulation has often been compared with thatof malignant invasion. In this paper, the terms "malignant"and "invasion" are denned and the characteristics of malignantcells are discussed. One of the best examples of invasion duringgastrulation takes place during the formation of the endodermin the chick, when the definitive endoblast invades the hypoblast.Experiments are described in which the hypoblast is invadedby a) definitive endoblast, b) other normal embryonic cells,and c) three types of human malignant cells. It was found thatnot only does the hypoblast react differently to normal andmalignant cells, but that the cell interactions differ alsoaccording to the type of malignant cells. In particular, thereare differences in the behaviour of the cells and in the amountof extracellular material laid down between the hypoblast andmalignant cells. It is concluded that even within the limitsof this experiment, chick gastrulation is not wholly analogousto malignant invasion.     

Catechol Oxidase in Suspension Cultures of Apple Fruit--The Effects of Growth Regulators

Growth and catechol oxidase activity were followed in suspensioncultures of cells derived from apple fruit. In cultures whichrequired the addition of hormones, enzyme activity was affectedby 2, 4-D (2, 4-dichlorophenoxyacetic acid) and kinetin viatheir effect on growth. Exogenous hormones did not affect catecholoxidase activity of habituated cultures. Ethylene and PCIB (-4-chlorophenoxyisobutyricacid) rapidly depressed enzyme activity in all cell fractions,but only at concentrations which repressed growth. Ethioninecaused an immediate decrease in enzyme activity which precededthe repression of growth. Ethionine did not inhibit enzyme activityin vitro. Possible mechanisms of the action of ethionine arediscussed and the formation of a specific inhibitor is hypothesized.     

Microsatellite isolation from the gall midge Spurgia capitigena (Diptera: Cecidomyiidae), a biological control agent of leafy spurge

Spurgia capitigena is a gall midge that has been released as a biological control agent of leafy spurge (Euphorbia esula), a noxious rangeland weed in North America. We isolated 15 microsatellite loci from S. capitigena with from two to 27 alleles at each locus. These markers will allow us to examine the structure and levels of neutral genetic variation in native and introduced populations.     

Challenges to estimating carbon emissions from tropical deforestation

An accurate estimate of carbon fluxes associated with tropical deforestation from the last two decades is needed to balance the global carbon budget. Several studies have already estimated carbon emissions from tropical deforestation, but the estimates vary greatly and are difficult to compare due to differences in data sources, assumptions, and methodologies. In this paper, we review the different estimates and datasets, and the various challenges associated with comparing them and with accurately estimating carbon emissions from deforestation. We performed a simulation study over legal Amazonia to illustrate some of these major issues. Our analysis demonstrates the importance of considering land-cover dynamics following deforestation, including the fluxes from reclearing of secondary vegetation, the decay of product and slash pools, and the fluxes from regrowing forest. It also suggests that accurate carbon-flux estimates will need to consider historical land-cover changes for at least the previous 20 years. However, this result is highly sensitive to estimates of the partitioning of cleared carbon into instantaneous burning vs. long-timescale slash pools. We also show that carbon flux estimates based on 'committed flux' calculations, as used by a few studies, are not comparable with the 'annual balance' calculation method used by other studies.     

Implications of future climate and atmospheric CO2 content for regional biogeochemistry,biogeography and ecosystem services across East Africa

We model future changes in land biogeochemistry and biogeography across East Africa. East Africa is one of few tropical regions where general circulation model (GCM) future climate projections exhibit a robust response of strong future warming and general annual‐mean rainfall increases. Eighteen future climate projections from nine GCMs participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment were used as input to the LPJ dynamic global vegetation model (DGVM), which predicted vegetation patterns and carbon storage in agreement with satellite observations and forest inventory data under the present‐day climate. All simulations showed future increases in tropical woody vegetation over the region at the expense of grasslands. Regional increases in net primary productivity (NPP) (18–36%) and total carbon storage (3–13%) by 2080–2099 compared with the present‐day were common to all simulations. Despite decreases in soil carbon after 2050, seven out of nine simulations continued to show an annual net land carbon sink in the final decades of the 21st century because vegetation biomass continued to increase. The seasonal cycles of rainfall and soil moisture show future increases in wet season rainfall across the GCMs with generally little change in dry season rainfall. Based on the simulated present‐day climate and its future trends, the GCMs can be grouped into four broad categories. Overall, our model results suggest that East Africa, a populous and economically poor region, is likely to experience some ecosystem service benefits through increased precipitation, river runoff and fresh water availability. Resulting enhancements in NPP may lead to improved crop yields in some areas. Our results stand in partial contradiction to other studies that suggest possible negative consequences for agriculture, biodiversity and other ecosystem services caused by temperature increases.     

Mechanisms of Sodium and Rubidium Uptake by Excised Barley Roots

Accumulation of sodium and rubidium by excised barley roots was investigated. The concentration isotherm yielded one absorption shoulder. Nevertheless, it is suggested that two mechanisms take part in the uptake of sodium and rubidium: One non-metabolic mechanism with an apparent participation at low external salt concentrations (< 1 mM) and at high concentrations (> 20 mM). Such a mechanism is almost unaffected by low temperature conditions and by metabolic inhibitors. Rubidium possesses a high affinity toward this non-metabolic system. The second mechanism is sensitive to metabolic inhibitors and to low temperature conditions. It dominates at intermediate external concentrations (1–20 mM). Sodium possesses high affinity towards this mechanism. The two mechanisms operate in a parallel manner beyond a diffusion barrier (= plasmamembrane) surrounding the cells. It is assumed that both the metabolic and the non-metabolic mechanisms operate in the entire concentration spectrum, but their relative contribution to the total uptake varies at different ranges.