The effect of salinity on the reproduction of coastal submerged macrophytes in experimental communities

The effects of salinity on the reproduction of coastal submerged macrophyte species were studied on samples of communities from six seasonal marshes in two outdoor experiments performed in autumn and in spring. The submerged macrophyte communities were submitted to five different salinity levels (0, 1, 2, 4 and 6 g/1 Cl^?1). In a companion paper (Grillas, van Wijck & Bonis 1993) three groups of species were distinguished on the basis of their biomass production over the salinity range 0 to 6 g/1 Cl^?1: (1) glycophytes (non-salt-tolerant species), (2) salt-tolerant species and (3) halo-phytes. This part of the study describes the impact of salinity on the reproduction of the individual species during the two experiments. The species differ in their capacity to reproduce in the autumn; only Zannichelliapedunculata and Tolypella hispánica were able to produce fruits in that season. For all species reproduction was greater in spring and strongly correlated with biomass, except for Chara canescens. Differences in reproductive effort over the salinity range amplified the halophytic nature of Ruppia marítima and Chara canescens and the intolerance of Callitriche truncata and Chara contraria. For the other species, reproductive effort did not differ significantly over the salinity range. Regarding the effect of salinity on biomass and reproductive effort of individual species, there were large differences in the total weight of propagules produced at the community level and in the relative contribution of individual species. The resulting quantitative changes in the species composition of the seed bank could affect the structure of the communities by their effects on the establishment and survival of species populations.     

Ecological and behavioral consequences of digestion in frugivorous animals

The postingestional effect of seed size and mass and nutrient composition on fruit profitability are reviewed. It is emphasized that profitability results from the interaction between fruit characteristics and the physiological and morphological traits of frugivores. The processes by which frugivores regurgitate or defecate seeds and the differential processing of the nutrient rich pulp and ballast in fruit are strongly dependent on the interaction between frugivore gut morphology and seed size. Euphonias that lack a functional gizzard defecate seeds, whereas tanagers that have a delete a functional gizzards regurgitate seeds. Some frugivores separate seeds from pulp and exocarp in the gizzard. It is hypothesized that the gizzard plays an important role in determining the postigestional fate of different pulp components. Although fruit nutrient content is often invoked as a determinant of frugivore feeding choices, studies that rely on proximal nutrient analysis, have often failed to find clear nutrient composition-preference correlations. It is argued that a partial reason for this failure is that proximal nutrient analysis ignores the complexities of fruit digestion. The ecological and physiological correlates of lipid and sugar assimilation are used to identify the limitations of traditional proximal nutrient analyses in fruit-frugivore studies. We suggest that recognizing the intricacies of the digestive characteristics of frugivores may reveal a much richer patterning in the interaction of frugivores with plants than has been previously hypothesized.     

Environmental gradients in a southern Europe estuarine system: Ria de Aveiro,Portugal implications for soft bottom macrofauna colonization

Four seasonal sampling surveys were carried out between December 1985 and September 1986 in Canal de Mira (Ria de Aveiro, Portugal). A total of 40 sampling stations, distributed over 13 transects, was used. Salinity, temperature, dissolved oxygen and pH of the water mass were measured. Sediment temperature, and salinity and pH of interstitial water were determined. Sediment variables also included granulometric composition and organic matter contents. Bottom macrofauna samples were collected at each station. Ordination (PCA and MDS) and classification of the sampling stations were performed, using the physicochemical and the biological data sets separately. Average linkage cluster analysis using the unweighted paired-group method, arithmetic averages, was used for both sets of data. With a salinity range from 35.1‰ to 0.0‰, Canal de Mira behaves like a tidally and seasonally poikilohaline estuary. Water temperature (8.5–24.7°C) decreased along the channel towards its inner part during the cold season; an inverse and more pronounced trend was observed during the hot season. Dissolved oxygen contents was generally high during the day (50% to 240% saturation). Oversaturation was observed throughout the growing season, with peaks in areas with large amounts of rooted vegetation. The pH values, largely correlated with dissolved oxygen, ranged from 6.8 to 8.9. Four types of sediment were present in Canal de Mira, medium and muddy sands being dominant. Two major gradients were identified: (i) a typical longitudinal estuarine gradient, associated with distance from the mouth, representing physicochemical variables such as tidal amplitude, salinity and temperature; this gradient was accompanied by an upstream increase in dominance; the community composition changes were mainly related to salinity; (ii) a lateral gradient, related to current velocity, depth and sediment composition; the subtidal community had a comparatively low species richness and abundance. Groups of stations could be recognized along the environmental gradients. Benthic community changes, however, appeared to be gradual rather than marked by abrupt transitions.     

RNA from LPS-stirnulated macrophages induces the release of tumour necrosis factor-alpha and interleukin-1 by resident macrophages

The effect of exogenous RNA on many cellular functions has been studied in a variety of eukaryotic cells but there are few reports on macrophages. In the present study, it is demonstrated that cytoplasmatic RNA extracted from rat macrophages stimulated with Escherichia coli lipopolysaccharide (LPS), referred to as L-RNA, induced the release of TNF-alpha and IL-1 from monolayers of peritoneal resident macrophages. The activity of L-RNA was not altered by polymyxin B but was abolished by ribonuclease (RNase) pretreatment, indicating the absence of LPS contamination and that the integrity of the polynucleotide chain is essential for this activity. Both the poly A(-) and poly A(+) fractions obtained from L-RNA applied to oligo(dT)-cellulose chromatography induced TNF-alpha and IL-1 release. The L-RNA-induced cytokine release was inhibited by dexamethasone and seemed to be dependent on protein synthesis since this effect was abolished by cycloheximide or actinomycin-D. The LPS-stimulated macrophages, when pre-incubated with [5-(3)H]-uridine, secreted a trichloroacetic acid (TCA) precipitable material which was sensitive to RNase and KOH hydrolysis, suggesting that the material is RNA. This substance was also released from macrophage monolayers stimulated with IL-1beta but not with TNF-alpha, IL-6 or IL-8. The substance secreted ((3)H-RNA) sediments in the 4-5S region of a 5-20% sucrose gradient. These results show that L-RNA induces cytokine secretion by macrophage monolayers and support the idea that, during inflammation, stimulated macrophages could release RNA which may further induce the release of cytokines by the resident cell population.     

Induction of phagocytic behaviour in human epithelial cells by Escherichia coli cytotoxic necrotizing factor type1

Cytotoxic necrotizing factor type 1 (CNF1) from strains of pathogenic Escherichia coli induces in human epithelial HEp-2 cells, a profound reorganization of the actin cytoskeleton into prominent stress fibres and membrane ruffles. We report here that this process is associated with induction of phagocytic-like activity. CNF1-treated cells acquired the ability to ingest latex beads as well as non-invasive bacteria such as Listeria innocua, which were taken as a model system. Uptake of bacteria was similar to pathogen-induced phagocytosis, since L. innocua transformed with DNA coding for the pore-forming toxin listeriolysln O behaved, with respect to intracellular growth, like the invasive, pathogenic species L. monocytogenes. Our results raise the possibility that, in vivo, pathogenic CNF1 -producing E. coli may invade epithelia by this novel induced phagocytic-like mechanism.     

Identification of a novel mechanism for LFA-1 organization during NK cytolytic response

The elimination of transformed and viral infected cells by natural killer (NK) cells requires a specialized junction between NK and target cells, denominated immunological synapse (IS). After initial recognition, the IS enables the directed secretion of lytic granules content into the susceptible target cell. The lymphocyte function-associated antigen (LFA)-1 regulates NK effector function by enabling NK-IS assembly and maturation. The pathways underlying LFA-1 accumulation at the IS in NK cells remained uncharacterized. A kinase anchoring protein 350 (AKAP350) is a centrosome/Golgi-associated protein, which, in T cells, participates in LFA-1 activation by mechanisms that have not been elucidated. We first evaluated AKAP350 participation in NK cytolytic activity. Our results showed that the decrease in AKAP350 levels by RNA interference (AKAP350KD) inhibited NK-YTS cytolytic activity, without affecting conjugate formation. The impairment of NK effector function in AKAP350KD cells correlated with decreased LFA-1 clustering and defective IS maturation. AKAP350KD cells that were exclusively activated via LFA-1 showed impaired LFA-1 organization and deficient lytic granule translocation as well. In NK AKAP350KD cells, activation signaling through Vav1 was preserved up to 10 min of interaction with target cells, but significantly decreased afterwards. Experiments in YTS and in ex vivo NK cells identified an intracellular pool of LFA-1, which partially associated with the Golgi apparatus and, upon NK activation, redistributed to the IS in an AKAP350-dependent manner. The analysis of Golgi organization indicated that the decrease in AKAP350 expression led to the disruption of the Golgi integrity in NK cells. Alteration of Golgi function by BFA treatment or AKAP350 delocalization from this organelle also led to impaired LFA-1 localization at the IS. Therefore, this study characterizes AKAP350 participation in the modulation of NK effector function, revealing the existence of a Golgi-dependent trafficking pathway for LFA-1, which is relevant for LFA-1 organization at NK-lytic IS.     

Influence of seasonal variation to the population growth and ecophysiology of Typha domingensis (Typhaceae)

Journal of Plant Research - Precipitation is an important climatic element that defines the hydrological regime, and its seasonal variation produces annual dry and wet periods in some areas. This...     

ROOT PROFILES AND COMPETITION BETWEEN THE INVASIVE,EXOTIC PERENNIAL,CARPOBROTUS EDULIS,AND TWO NATIVE SHRUB SPECIES IN CALIFORNIA COASTAL SCRUB

The mat-forming succulent, Carpobrotus edulis (Aizoaceae), surrounds and grows over many native plant species in California coastal communities. Two shrub species, Haplopappus ericoides and H. venetus var. sedoides, were found to have shallow root systems that occupied the same soil depths as those of C. edulis. In the presence of C. edulis, the normal rooting profiles of the shrubs were displaced downward, although partial overlap with C. edulis remained. Removal of C. edulis from around individuals of both shrub species resulted in higher predawn xylem pressure potentials in shrubs from the removal treatments as compared to controls, suggesting that the surrounding C. edulis was utilizing water that would otherwise have been available to these shrubs. In H. ericoides, predawn xylem pressure potentials of removal treatment shrubs remained higher than those of the controls throughout the remainder of the dry season even though these shrubs showed a marked increase in canopy area after removal of surrounding C. edulis. Removal of C. edulis from around H. venetus also initially led to higher predawn xylem pressure potentials in the removal shrubs as compared to the controls and increased production of new leaves. After this initial period the predawn xylem pressure potentials of the removal shrubs were not significantly different from those of controls, suggesting that the demand for water by the increased leaf areas eventually matched the enhanced water availability resulting from C. edulis removal. Also, the morphology of H. venetus shrubs changed to that more typical of unaffected individuals. Thus, C. edulis significantly affected not only the water relations of these two shrub species but also their shoot sizes and overall morphologies.     

Differentiation in sex investment by clones and populations of Daphnia

Dormancy is an ecological strategy by which organisms avoid stressful environments, but it also can have genetic consequences. Many facultative parthenogens shift from asexual to sexual reproduction to enter dormancy. Hence, conditions that favour dormancy are predicted to select for more sex, which should increase clonal diversity. We examined lake populations of Daphnia that face different ecological risks to remaining active year‐round, and quantified the extent to which they have differentiated in their investment in dormancy and sex. There was substantial genetic variation among populations and clones for sex induction and production of dormant eggs, and striking evidence of gender specialization. We also observed a positive association between the magnitudes of population‐level investment in dormancy and of variance among clones in sex induction. These results document an ecological gradient in dormancy that is manifest as a genetic gradient in clonal variation for the propensity to engage in sex.