Phytoplankton response to light and internal phosphorus loading from sediment release

1. A 2 × 2 factorial design was employed to look at the influence of two levels of phosphorus (P; high and low) and two levels of light (high and low) and their interactions, on phytoplankton abundance, elemental tissue composition and community structure in two seasons (April and June) of 2005. 2. A novel feature of the experiment was the creation of high and low P levels by manipulating sediment core conditions in the laboratory. Sediment cores were incubated with their associated overlaying water column from four different sites in Mona Lake, Michigan, under anaerobic or aerobic conditions, respectively. 3. After 24 days, the water overlaying the sediment cores was collected and used as growth media for phytoplankton collected from Mona Lake. Phytoplankton communities were grown in the laboratory in the high or low P water, and subjected to high (250 μmol m^?2 s^?1) or low (10 μmol m^?2 s^?1) light for 9 (April) or 14 (June) days. 4. In the April experiment, high P treatments resulted in significantly higher chlorophyll‐a concentrations, significantly lower C : P ratios from two of the four sites, and greater dominance by Scenedesmus at all sites relative to low P treatments. High light generally led to higher chlorophyll‐a concentrations, higher C : P ratios and greater Scenedesmus and Fragilaria biovolume at all sites. A significant interaction was measured between P and light for chlorophyll‐a and Scenedesmus biovolume, suggesting the influence of P was more apparent at high light than at low light levels. 5. In the June experiment, high P increased ash‐free dry mass (AFDM), lowered C : P ratios and resulted in increased Pediastrum biovolume. High light levels led to greater chlorophyll‐a concentrations, AFDM and C : P ratios, as well as increased biovolumes of Scendesmus, Pediastrum and Fragilaria. A significant interaction was found between P and light for all three taxa, as the positive influence of P was more pronounced at high light levels. 6. The results of our study demonstrate that sediment‐derived P stimulates phytoplankton growth, but that its effect on phytoplankton dynamics is modulated by other factors, such as light.     

The outcome of the invasion of Florida lakes by Daphnia lumholtzi

1. We examined 7–12 years of monthly to quarterly historical data from 15 lakes in FL, U.S.A. to determine the extent and outcome of invasion by the alien cladoceran Daphnia lumholtzi Sars. 2. The alien species was found in 10 of the 15 lakes, including Florida’s three largest lakes: Okeechobee, George and Apopka. All the surveyed lakes had resident populations of the smaller native species Daphnia ambigua Scourfield. 3. In most of the lakes, D. ambigua occurred seven to ninefold more often in plankton samples than D. lumholtzi, and at 10‐ to 100‐fold higher maximal densities. One exception was a small lake in central Florida (Lake Jesup), where D. lumholtzi attained high densities on several occasions in the 10 years of sampling. 4. In Lake Okeechobee, where data were of sufficient quality and quantity to perform statistical analyses, the results of canonical correlation analysis indicated that high densities of D. lumholtzi were correlated with lower concentrations of suspended solids, high algal biomass and higher temperature, whereas the opposite conditions were correlated with high densities of D. ambigua. 5. Based on the majority of data, D. lumholtzi has successfully invaded many lakes in Florida, yet it has not become a substantive component of the zooplankton. Additional research is needed to determine whether resources, fish predation or some other factor is responsible for this outcome of invasion.     

Heterogeneity of Intermediate Filament Expression in Vascular Smooth Muscle: A Gradient in Desmin Positive Cells from the Rat Aortic Arch to the Level of the Arteria Iliaca Communis

The display of the two distinct intermediate filament proteins, desmin and vimentin, in rat vascular smooth muscle tissue was studied by immunofluorescence microscopy on frozen sections of aorta and other blood vessels. Vascular smooth muscle cells present in these vessels always appeared rich in vimentin. However, staining of sections covering six distinct but contiguous parts of the aorta showed that the number of desmin containing cells was low distal to the truncus brachiocephalicus, but increases until in distal parts of the aorta and in the arteria iliaca communis almost all cells appear positive for desmin. Thus blood vessels show heterogeneity of intermediate filament expression not only in cross-section but can also display heterogeneity along their length. Muscular arteries such as the renal artery and the arteria femoralis, as well as arterioles and veins including the vena jugularis and the vena cava also contain desmin. Thus it may be that low numbers of desmin-positive cells are typical of elastic arteries, while muscular arteries and other blood vessels are characterized by large numbers of desmin-positive cells. We discuss whether desmin-positive and desmin-negative vascular smooth muscle cells may perform different functions and raise the possibility that desmin expression may coincide with the turn on of a specially regulated contractility program.     

Indirect Immunofluorescence Microscopy of Microtubular Structures in Male Germ Cells of Wildtype and l(3)pl (lethal-polyploid) Drosophila hydei

Tubulin-containing structures of the male germ cells of Drosophila hydei crossreact in indirect immu-nofluorescence microscopy with antibody directed against homogeneous porcine brain tubulin. There is no detectable difference in reactivity between germ cells of wildtype flies and the mutant l(3)pl (lethal-polyploid) which is characterized by microtubular abnormalities. However, the technique of indirect immunofluorescence microscopy allows the direct visualization of several abnormalities in the arrangement of the microtubular system of the mutant, particularly in the axonemal complex.     

Respiratory pathways in aged soybean seeds

Respiratory activities in soybean seeds (Glvcine max (L.) Merr. cv. Chippewa 64) have been examined in the first minutes after water imbibition and after three hours of imbibition, using either particles or intact axes. Cyanide and azide were utilized as inhibitors of the cytochrome oxidase pathway of respiration, and SHAM inhibitions were interpreted as effects on the alternative pathway, since in unaged axes inhibitions by SHAM were obtained only when respiratory activity had either been restricted with inhibitors of the cytochrome oxidase pathway or expanded by an uncoupler (CCCP). From the experiments with these inhibitors, it is suggested that unaged seeds utilize both respiration pathways in the cotyledon but only the cytochrome pathway in the axis. Accelerated aging causes a marked deterioration of respiration, especially that through the cytochrome pathway, and there is an associated engagement of the alternative pathway in the seed axis. It is suggested that the lowering of respiratory activity and the shift in respiratory pathways may play a major role in the decline of germinability and vigor.