Effects of ultraviolet-B radiation on plants during mild water stress. IV. The insensitivity of soybean internal water relations to ultraviolet-B radiation

The combined effects of ultraviolet-B (UV-B, 280–320 nm) radiation and water stress were investigated on the water relations of greenhouse grown soybean [ Glycine max (L.) Merr. cv. Essex]. On a weighted (Caldwell 1971), total daily dose basis, plants received either 0 or 3 000 effective J m² UV-B_BE supplied by filtered FS-40 sunlamps. The latter dose simulated the solar UV-B radiation anticipated at College Park, Maryland, U.S.A. (39°N latitude) in the event that the global stratospheric ozone column is reduced by 25%. Plants were either well-watered or preconditioned by drought stress cycles. Diurnal measurements of water potential and stomatal conductance were made on the youngest fully expanded leaf. Various internal water relations parameters were determined for detached leaves. Plants were monitored before, during and after water stress. There were no significant differences in leaf water potential or stomatal conductance between treatments before plants were preconditioned to water stress. However, drought stress resulted in significantly lower midday and afternoon leaf water potentials and lower leaf conductances as compared to well-watered plants. UV-B radiation had no additional effect on leaf water potential; however, UV did result in lower leaf conductances in plants preconditioned to water stress. Turgid weight:dry weight ratio, elastic modulus, bound water and relative water content were unaffected by UV-B radiation. Osmotic potentials at full and zero turgor were significantly lower in the drought stressed treatments as compared to well-watered plants.     

Effects of below- and aboveground competition from the vines Lonicera japonica and Parthenocissus quinquefolia on the growth of the tree host Liquidambar styraciflua

Detrimental effects of vines on tree growth in successional environments have been frequently reported. Little is known, however, about the relative importance of below and aboveground competition from vines on tree growth. The objective of this study was to quantify and compare the growth responses of Liquidambar styraciflua saplings to below and/or aboveground competition with the exotic evergreen vine, Lonicera japonica (Japanese honeysuckle), and the native deciduous vine, Parthenocissus quinquefolia (Virginia creeper). Soil trenching and/or vine-trellising were used to control the type of vine competition experienced by trees. Comparisons among untrenched treatments tested for effects of belowground competition. Comparisons among trenched treatments tested for effects of aboveground competition. After two growing seasons, Lonicera japonica had a greater effect on the growth of L. styraciflua than did P. quinquefolia. This effect was largely due to root competition, as canopy competition only had a negative effect on tree growth when it occurred in combination with root competition. Leaf expansion was consistently and similarly affected by all treatments which involved belowground competition.     

The pericentriolar material in Chinese hamster ovary cells nucleates microtubule formation

The structure and function of the centrosomes from Chinese hamster ovary (CHO) cells were investigated by electron microscopy of negatively stained wholemount preparations of cell lysates. Cells were trypsinized from culture dishes, lysed with Triton X-100, sedimented onto ionized, carbon-coated grids, and negatively stained with phosphotungstate. The centrosomes from both interphase and dividing cells consisted of pairs of centrioles, a fibrous pericentriolar material, and a group of virus-like particles which were characteristic of the CHO cells and which served as markers for the pericentriolar material. Interphase centrosomes anchored up to two dozen microtubules when cells were lysed under conditions which preserved native microtubules. When Colcemid-blocked mitotic cells, initially devoid of microtubules, were allowed to recover for 10 min, microtubules formed at the pericentriolar material, but not at the centrioles. When lysates of Colcemid-blocked cells were incubated in vitro with micotubule protein purified from porcine brain tissue, up to 250 microtubules assembled at the centrosomes, similar to the number of microtubules that would normally form at the centrosome during cell division. A few microtubules could also be assembled in vitro onto the ends of isolated centrioles from which the pericentriolar material had been removed, forming characteristic axoneme- like bundles. In addition, microtubules; were assembled onto fragments of densely staining, fibrous material which was tentatively identified as periocentriolar material by its association of CHO can initiate and anchor microtubules both in vivo and in vitro.     

Interactive effects of water stress and xylem-limited bacterial infection on the water relations of a host vine

Xylella fastidiosa, a xylem-limited bacterial pathogen that causes bacterial leaf scorch in its hosts, has a diverse and extensive host range among plant species worldwide. Previous work has shown that water stress enhances leaf scorch symptom severity and progression along the stem in Parthenocissus quinquefolia infected by X. fastidiosa. The objective here was to investigate the mechanisms underlying the interaction of water stress and infection by X. fastidiosa. Using the eastern deciduous forest vine, P. quinquefolia, infection and water availability were manipulated while measuring leaf water potentials (psi(L)), stomatal conductance (g(s)), whole shoot hydraulic conductance (K(h)), per cent xylem embolism, and xylem vessel dimensions. No significant differences in any of the physiological measurements were found between control and infected plants prior to drought. Drought treatment significantly reduced psi(L) and g(s) at all leaf positions throughout the day in late summer in both years of the study. In addition, infection significantly reduced psi(L) and g(s) in the most basal leaf positions in late summer in both years. Whole shoot hydraulic conductance was reduced by both low water and infection treatments. However, per cent embolized vessels and mean vessel diameter were affected by drought treatment only. These results imply that the major effect of infection by X. fastidiosa occurs due to reduced hydraulic conductance caused by clogging of the vessels, and not increased cavitation and embolism of xylem elements. The reduced K(h) caused by X. fastidiosa infection acts additively with the water limitation imposed by Drought stress.     

Genetic diversity in the invasive <Emphasis Type="Italic">Rubus phoenicolasius</Emphasis> as compared to the native <Emphasis Type="Italic">Rubus argutus</Emphasis> using inter-simple sequence repeat (ISSR) markers

Invasive species are one of most significant factors in human-influenced global change. Management actions that prevent the spread and impacts of invasive species require knowledge of their ecological and genetic characteristics. The genetic characteristics of the invasive wine raspberry, Rubus phoenicolasius Maxim. (Rosaceae) and the native sawtooth blackberry, Rubus argutus Link, were examined in two forest habitats on the Maryland Coastal Plain. Using inter-simple sequence repeat (ISSR) markers we quantified the genetic diversity of both species. We analyzed genetic diversity using analysis of molecular variance (AMOVA) and found less genetic diversity in the invasive species, R. phoenicolasius, with variation between sites was 0.418 between sites and 0.075 within sites as compared to the native, R. argutus, where the variation between sites was 1.538 and 0.370 within sites. The lower genetic diversity in the invasive may be due to a history of limited introductions or frequent self-fertilization and clonal reproduction.     

Porcine reproductive and respiratory syndrome virus (PRRSV) infection spreads by cell-to-cell transfer in cultured MARC-145 cells, is dependent on an intact cytoskeleton, and is suppressed by drug-targeting of cell permissiveness to virus infection

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is the etiologic agent of PRRS, causing widespread chronic infections which are largely uncontrolled by currently available vaccines or other antiviral measures. Cultured monkey kidney (MARC-145) cells provide an important tool for the study of PRRSV replication. For the present study, flow cytometric and fluorescence antibody (FA) analyses of PRRSV infection of cultured MARC-145 cells were carried out in experiments designed to clarify viral dynamics and the mechanism of viral spread. The roles of viral permissiveness and the cytoskeleton in PRRSV infection and transmission were examined in conjunction with antiviral and cytotoxic drugs.

Results

Flow cytometric and FA analyses of PRRSV antigen expression revealed distinct primary and secondary phases of MARC-145 cell infection. PRRSV antigen was randomly expressed in a few percent of cells during the primary phase of infection (up to about 20–22 h p.i.), but the logarithmic infection phase (days 2–3 p.i.), was characterized by secondary spread to clusters of infected cells. The formation of secondary clusters of PRRSV-infected cells preceded the development of CPE in MARC-145 cells, and both primary and secondary PRRSV infection were inhibited by colchicine and cytochalasin D, demonstrating a critical role of the cytoskeleton in viral permissiveness as well as cell-to-cell transmission from a subpopulation of cells permissive for free virus to secondary targets. Cellular expression of actin also appeared to correlate with PRRSV resistance, suggesting a second role of the actin cytoskeleton as a potential barrier to cell-to-cell transmission. PRRSV infection and cell-to-cell transmission were efficiently suppressed by interferon-γ (IFN-γ), as well as the more-potent experimental antiviral agent AK-2.

Conclusion

The results demonstrate two distinct mechanisms of PRRSV infection: primary infection of a relatively small subpopulation of innately PRRSV-permissive cells, and secondary cell-to-cell transmission to contiguous cells which appear non-permissive to free virus. The results also indicate that an intact cytoskeleton is critical for PRRSV infection, and that viral permissiveness is a highly efficient drug target to control PRRSV infection. The data from this experimental system have important implications for the mechanisms of PRRSV persistence and pathology, as well as for a better understanding of arterivirus regulation.     

A concept for improving Atlantic salmon Salmo salar smolt migration past hydro power intakes

In this study, cost effective (in terms of reducing loss of power production) measures for increasing bypass migration of Atlantic salmon Salmo salar were developed and tested by establishing statistical models for timing of smolt migration and favourable diversion of water to the bypass. Initial tracking of radio-tagged smolts showed very low bypass migration under normal hydropower operations. Bypass migration increased when bypass discharge was experimentally increased and a model was developed that described relationships between total river discharge, bypass diversion and smolt migration route. Further improvements were obtained by installing two strobe lights at the power-production tunnel entrance that increased bypass migration during the night, but not during daytime. According to the behaviour of radio-tagged fish, the implemented measures contributed to increasing the annual percentage of bypass migration from 11 to 64%, and according to model predictions to 60-74% when the hydropower facilities were operated according to the developed models. To ensure correct timing of discharge diversion a smolt migration model was developed based on environmental variables that could successfully predict the general pattern of migration timing. The concept presented for improving smolt migration past hydropower intakes should be applicable in many systems where migration past hydropower installations cannot easily be solved by screening systems.     

An experimental study of the multiple effects of brown trout Salmo trutta on the bioenergetics of two Arctic charr Salvelinus alpinus morphs

This study investigated the importance of competition with brown trout Salmo trutta as a driver of the morphological and behavioural divergence of two morphs of Arctic charr Salvelinus alpinus. The morphs originated from two lakes differing in absence or presence of the competitor. The bioenergetics and behaviour of S. alpinus were quantified in replicate experimental enclosures (mean volume: 150 m(3) ) stocked with 15 S. alpinus of one morph or the other and in the absence or presence of nine S. trutta. The presence of S. trutta decreased growth rate, affected food consumption and increased activity costs in S. alpinus, but provided little support for the hypothesis that competition with S. trutta is a major driver of the divergence of the two S. alpinus morphs. Both morphs responded similarly in terms of mean growth and consumption rates per enclosure, but the association between individual morphology and growth rate reversed between allopatric and sympatric enclosures. While the activity patterns of the two morphs were unaffected by the presence of S. trutta, their swimming speed and activity rate differed. Since the profound differences in the structure of the physical habitat of the source lakes provided a more likely explanation for the difference observed among these two morphs than interspecific competition, it is hypothesized that physical habitat may sometimes be a significant driving force of the phenotypic divergence.