The determination of the apparent dissociation constants of arsenic acid in water

The apparent dissociation constants for arsenic acid in seawater, based on a free molal hydrogen scale, were determined in artificial seawater over a range of salinities and temperatures. A comparison between constants determined in a sodium chloride solution and artificial seawater of the same ionic strength suggests that a significant amount of the reactive arsenate in seawater is ion paired with cations other than sodium...

Insulin-like signalling to the maternal germline controls progeny response to osmotic stress

In 1893 August Weismann proposed that information about the environment could not pass from somatic cells to germ cells, a hypothesis now known as the Weismann barrier. However, recent studies have indicated that parental exposure to environmental stress can modify progeny physiology and that parental stress can contribute to progeny disorders. The mechanisms regulating these phenomena are poorly understood. We report that the nematode Caenorhabditis elegans can protect itself from osmotic stress by entering a state of arrested development and can protect its progeny from osmotic stress by increasing the expression of the glycerol biosynthetic enzyme GPDH-2 in progeny. Both of these protective mechanisms are regulated by insulin-like signalling: insulin-like signalling to the intestine regulates developmental arrest, while insulin-like signalling to the maternal germline regulates glycerol metabolism in progeny. Thus, there is a heritable link between insulin-like signalling to the maternal germline and progeny metabolism and gene expression. We speculate that analogous modulation of insulin-like signalling to the germline is responsible for effects of the maternal environment on human diseases that involve insulin signalling, such as obesity and type-2 diabetes

The Effects of Seed Size on Hybrids Formed between Oilseed Rape (Brassica napus) and Wild Brown Mustard (B. juncea)

Background : Seed size has significant implications in ecology, because of its effects on plant fitness. The hybrid seeds that result from crosses between crops and their wild relatives are often small, and the consequences of this have been poorly investigated. Here we report on plant performance of hybrid and its parental transgenic oilseed rape (Brassica napus) and wild B. juncea, all grown from seeds sorted into three seed-size categories.[br/] Methodology/Principal Findings : Three seed-size categories were sorted by seed diameter for transgenic B. napus, wild B. juncea and their transgenic and non-transgenic hybrids. The seeds were sown in a field at various plant densities. Globally, small-seeded plants had delayed flowering, lower biomass, fewer flowers and seeds, and a lower thousand-seed weight. The seed-size effect varied among plant types but was not affected by plant density. There was no negative effect of seed size in hybrids, but it was correlated with reduced growth for both parents.[br/] Conclusions : Our results imply that the risk of further gene flow would probably not be mitigated by the small size of transgenic hybrid seeds. No fitness cost was detected to be associated with the Bt-transgene in this study

Adaptive Value of Phenological Traits in Stressful Environments: Predictions Based on Seed Production and Laboratory Natural Selection

Phenological traits often show variation within and among natural populations of annual plants. Nevertheless, the adaptive value of post-anthesis traits is seldom tested. In this study, we estimated the adaptive values of pre- and post-anthesis traits in two stressful environments (water stress and interspecific competition), using the selfing annual species Arabidopsis thaliana. By estimating seed production and by performing laboratory natural selection (LNS), we assessed the strength and nature (directional, disruptive and stabilizing) of selection acting on phenological traits in A. thaliana under the two tested stress conditions, each with four intensities. Both the type of stress and its intensity affected the strength and nature of selection, as did genetic constraints among phenological traits. Under water stress, both experimental approaches demonstrated directional selection for a shorter life cycle, although bolting time imposes a genetic constraint on the length of the interval between bolting and anthesis. Under interspecific competition, results from the two experimental approaches showed discrepancies. Estimation of seed production predicted directional selection toward early pre-anthesis traits and long post-anthesis periods. In contrast, the LNS approach suggested neutrality for all phenological traits. This study opens questions on adaptation in complex natural environment where many selective pressures act simultaneously

The Determination of the Apparent Dissociation Constants of Arsenic Acid in Seawater

The apparent dissociation constants for arsenic acid in seawater, based on a free molal hydrogen scale, were determined in artificial seawater over a range of salinities and temperatures. A comparison between constants determined in a sodium chloride solution and artificial seawater of the same ionic strength suggests that a significant amount of the reactive arsenate in seawater is ion paired with cations other than sodium. Under typical seawater conditions, arsenic acid appears to be less dissociated than its analogue, phosphoric acid. A series of conversion factors was determined so that these constants could also be applied in conjunction with pH measurements in seawater based on the NBS activity scale

Accumulation of sediments, trace metals (Pb, Cu) and total hydrocarbons in Narragansett Bay, Rhode Island

The accumulation of sediments, trace metals and hydrocarbons has been estimated from the analysis of the sediment from six coring sites in Narragansett Bay. Radionuclides (234Thxs, 210Pbxs, 239,240Pu) with known input functions and trace metals (Cu, Pb) were used. We estimate that 6·9 × 104 tons of sediments, 51-90 tons of Pb, 72-100 tons of Cu and 400-1000 tons of total hydrocarbons accumulate annually under present conditions in the bay. This represents 64-117% (Pb), 89-123% (Cu) and 23-58% (hydrocarbons), respectively, of present day inputs to the bay. Furthermore, close to 100% of the particle-reactive radionuclides 210Pb and 239,240Pu accumulate in the bay. Present day inputs to the bay were calculated independently as 77-80 tons Pb and 81 tons of Cu. Sewage effluents were the dominant source of Cu, whereas atmospheric deposition and urban runoff were most important for Pb. Dredging activities by the U.S. Army Corps of Engineers between 1946 and 1971 removed more sediments from the bay than would have accumulated during the same time in the undredged areas of the bay. Copper smelting and coal mining on the shores of the upper bay during 1866-1880 left an imprint in the sediments which is still evident. Model derived accumulation rates of Pb, Cu and coal during that time were 3-4 times present-day inputs. © 1984

Control of nutrient concentrations in the Seekonk-Providence River region of Narragansett Bay, Rhode Island

Six synoptic samplings of nutrient concentrations of the water column and point-source inputs (rivers, sewage treatment plants) were conducted in the Seekonk-Providence River region of Narragansett Bay. Concentrations of nutrients (NH4+, NO2-+NO3-, PO4-3, dissolved silicon, particulate N, particulate C) were predicted using a conservative, two-layer box model in order to assess the relative influence of external inputs and internal processes on observed concentrations. Although most nutrients were clearly affected by processes internal to the system, external input and mixing explained most of the variability in and absolute magnitude of observed concentrations, especially for dissolved constituents. In the bay as a whole, two functionally distinct regions can now be identified: the Seekonk-Providence River, where dissolved nutrient concentrations are externally controlled and lower Narragansett Bay where internal processes regulate the behavior of nutrients. A preliminary nitrogen budget suggests that the Seekonk-Providence River exports some 95% of the nitrogen entering the system via point sources and bottom water from upper Narragansett Bay. © 1990 Estuarine Research Federation