Experiments with Spores of Aquatic Hyphomycetes: I. Sedimentation, and Impaction on Smooth Surfaces

Techniques are described for the production of heavy concentrationsof aquatic Hyphomycete spores, for estimating the spore concentration,the sedimentation rate of spores and their trapping efficiencyon smooth cylinders. No correlation could be discovered betweenthe rates of sedimentation and spore shape. Trapping experimentsshowed that the trapping efficiency of the tetraradiate sporeswas higher than that of spores of different shape. It is suggestedthat the higher efficiency might be the result of contact ofthe tetraradiate spore at three points on a surface.     

LOCALIZATION OF SH-PTP1 TO SYNAPTIC VESICLES: A POSSIBLE ROLE IN NEUROTRANSMISSION

The tyrosine kinase pp60^src is known to phosphorylate synaptophysin and in doing so may regulate neurotransmitter release. The tyrosyl phosphorylated state of synaptophysin is dependent on pp60^src kinase and the unknown protein tyrosine phosphate phosphohydrolase (PTPase, EC 3.1.3.48). Here we report the protein tyrosine phosphate phosphohydrolase SH-PTP1, to associate with synaptic vesicles and interact with synaptophysin. These studies identify SH-PTP1 as a new member of the secretory machinery at the nerve terminal and suggest its involvement in neurotransmission.     

Caribbean octocorals record changing carbon and nitrogen sources from 1862 to 2005

During the last century, the global biogeochemical cycles of carbon (C) and nitrogen (N) have been drastically altered by human activities. A century of land‐clearing and biomass burning, followed by fossil fuel combustion have increased the concentration of atmospheric CO₂ by approximately 20%, and since the mid‐1900s, the use of agricultural fertilizers has been the primary driver of an approximate 90% increase in bioavailable N. Geochemical records obtained through stable isotope analysis of terrestrial and marine biota effectively illustrate rising anthropogenic C inputs. However, there are fewer records of anthropogenic N, despite the enormous magnitude of change and the known negative effects of N on ecosystem health. We used stable isotope values from independent octocorals (gorgonians) sampled across the Western Atlantic over the last 143 years to document human perturbations of the marine C and N pools. Here, we demonstrate that in sea plumes δ¹³C values and in both sea plumes and sea fans δ¹⁵N values declined significantly from 1862 to 2005. Sea plume δ ¹³C values were negatively correlated with increasing atmospheric CO₂ concentrations and corroborate known rates of change resulting from global fossil fuel combustion, known as the Suess effect. We suggest that widespread input of agricultural fertilizers to near‐shore coastal waters is the dominant driver for the decreasing δ ¹⁵N trend, though multiple anthropogenic sources are likely affecting this trend. Given the interest in using δ ¹⁵N as an indicator for N pollution in aquatic systems, we highlight the risk of underestimating contributions of pollutants as a result of source mixing as demonstrated by a simple isotope‐mixing model. We conclude that signals of major human‐induced perturbations of the C and N pools are detectable in specimens collected over wide geographic scales, and that archived materials are invaluable for establishing baselines against which we can assess environmental change.     

Modelling adaptive management strategies for coping with the impacts of climate variability and change on riverine algal blooms

The impact of climate change on hydrology and water resources is one of the most critical issues facing the world in the next few decades. In particular, there is a need to quantify the risks associated with maintaining the security of resource quantity and quality, and to assess the effectiveness of potential management strategies. In this paper, we assess the impacts of climate variability and change on one aspect of river health. A simple model of Anabaena algal bloom occurrence at a weir pool in the lower Murrumbidgee River, Australia, has been coupled to a catchment model that is used to simulate streamflow, irrigation demand and diversions, dam water storage and releases, and decision-making by both irrigators and managers. Long-term climate data are obtained from a statistical downscaling algorithm, which, when applied to global climate model predictions can provide climate data suitable for driving the coupled model under a variety of climatic scenarios. The coupled model is then used to assess the impact of climate variability and projected climate change on the frequency, duration and magnitude of Anabaena blooms. The impact of two management strategies for bloom control are also assessed and it is shown that even a single, quite simple, resource-neutral, adaptive management strategy has the potential to substantially reduce the occurrence and impact of algal blooms and to more than compensate for the deleterious impacts of climate change. This result supports the notion that planning for the future can lead to positive outcomes in the present.     

The effect of resistant solanaceous plants on the sex ratio of Heterodera rostochiensis and the use of the sex ratio to assess the frequency and genetic constitution of pathotypes

The sex ratios of two Heterodera rostochiensis populations were compared on fifteen solanaceous plants. Larvae did not mature in the roots of Atropa belladona, Datura stramonium or Nicotiana tabacum but adults were produced on the other plants, on some only males and on others, males and females. With two other populations, but not with a third, the percentage of larvae that became female on a potato hybrid with a dominant gene for resistance derived from Solanum tuberosum ssp. andigena increased during successive generations on the hybrid in accordance with the hypothesis that such larvae are double recessives (aa). Fewer larvae became adult in plants with two dominant genes for resistance than in plants with one, and such plants probably exerted selection of both males and females. A population from St Brelades (Jersey) produced fewer females and more males on the susceptible variety Arran Banner than did either the Thorney (Cambs.) or Aberystwyth populations. A much greater percentage of larvae from the St Brelades population became female on an ex andigena hybrid derived from CPC 1690 than on one derived from CPC 1685.     

Systematic distribution of foliar trichome types in Crotovt (Euphorbiaceae)

Variation in foliar trichomes in Croton (Euphorbiaceae) is reviewed, and the terminology clarified by redefinitions and illustrations of terms. Evolution of trichome types appears to proceed from branched (stellate or fasciculate) hairs to simple and dendritic ones. A systematic enumeration characterizes the trichome morphology in 36 of the 40 sections, with citation of the 120 species examined.     

Water stress and sporangial emptying in Achlya (Saprolegniaceae)

Time-course experimenls demonstrate that sporangial emptying in Achlya inlricata is inhibited by experimental depression of the external osmotic potential. The sporangial wall is a macromolecular sieve, impermeable to polyethylene glycols (PEGs) with molecular weight 3350. The process of emptying can be precisely manipulated using PEG-8000 which suggests that spore discharge in an aqueous environment is effected by a reduction in the osmotic potential of the sporangial lumen relative to the external solution.     

The influence of landscape position on lakes in northern Wisconsin

1. Using data from the North Temperate Lakes Long-Term Ecological Research site in northern Wisconsin, we present a series of examples illustrating how landscape setting can influence the static and dynamic aspects of many physical, chemical and biological properties of lakes. 2. One important landscape attribute is the hydrologic position of a lake within the regional flow regime. Lake position determines the relative importance of groundwater and precipitation input to a lake, with lakes high in the landscape receiving a greater proportion of their input waters from precipitation than lakes lower in the landscape. Landscape position is strongly correlated with the concentration of base cations such as calcium and magnesium. 3. Landscape position also influences how lakes respond to drought conditions. Lakes high in the landscape responded to a 4-year drought with decreases in calcium mass, whereas lakes low in the landscape increased in mass of calcium. During extended dry conditions, these differential responses of lakes suggest that lakes already low in calcium (i.e. in a high position in the flow system) will have further reductions in calcium concentrations. These reductions could decrease the number of lakes offering suitable habitat for organisms such as crayfish and snails whose distributions are limited by calcium. 4. Landscape position also affects silica concentrations in lakes, with lakes low in the landscape having silica concentrations up to three orders of magnitude greater than lakes high in the landscape. Differences in silica concentration affect robustness of freshwater sponge spicules which can potentially alter some aspects of the dynamics of littoral zone food webs. 5. Landscape position can influence the vertical distribution of primary production. Concentrations of dissolved organic carbon are affected by landscape setting and can influence vertical light penetration, thus affecting the depth at which primary production can occur. 6. Lake area and fish species richness are correlated with landscape position: larger, species-rich lakes are low in the landscape, whereas smaller lakes with fewer species tend to be high in the landscape. 7. By taking a landscape-scale view, in addition to the more usual lake-specific view, it is possible to reach a more robust understanding of lake dynamics and avoid some of the problems associated with extrapolating from single lake results.     

Changes in the Duration of the Mitotic Cycle Induced by Colchicine and Indol-3yl-acetic Acid in Vicia faba Roots

Cells of root meristems of Vicia faba were labelled with tritiatedthymidine and treated with colchicine or IAA or both. The effectsof these compounds on the duration of the mitotic cycle andits constituent phases have been determined using the labelledmitoses wave method of Quastler and Sherman. Colchicine shortensthe mitotic cycle of the cells in interphase at the time oftreatment; it appears to stimulate cells in G1 or early S tocomplete interphase faster than untreated cells. The affectedcells arrive at mitosis 9–12 h after the beginning oftreatment and contribute to the increase in mitotic index seenafter treatment with colchicine. Treatment with IAA did notaffect cells in G2 but it delayed cells in S; this results ina temporary fall in M.I. The effect of IAA in prolonging interphasewas also seen in roots treated with colchicine and IAA; thetetraploid cells induced by colchicine take longer to reachmetaphase than cells treated only with colchicine. The resultssuggest that colchicine and IAA affect different phases of thecell cycle.