ALBERT

Notes: Abstract The vas deferens forms part of the male reproductive tract and extends from the cauda epididymis to the prostate. Using the patch clamp technique, we have identified a Ca2+-activated, voltage-dependent, maxi K+ channel on the apical membrane of epithelial cells cultured from human fetal vas deferens. The channel had a conductance of ∼250 pS in symmetrical 140 mm K+ solutions, and was highly selective for K+ over Na+. Channel activity was increased by depolarization and by an elevation of bath (cytoplasmic) Ca2+ concentration, and reduced by cytoplasmic Ba2+ (5 mm) but not by cytoplasmic TEA (10 mm). Channel activity was also dependent on the cation bathing the cytoplasmic face of the membrane, being higher in a Na+-rich compared to a K+-rich solution. We estimated that up to 600 maxi K+ channels were present on the apical membrane of a vas cell, and that their density was 1–2 per μ2 of membrane. Activity of the channel was low on intact cells, suggesting that it does not contribute to a resting K+ conductance. However, fluid in the lumen of the human vas deferens has a high K+ concentration and we speculate that the maxi K+ channel could play a role in transepithelial K+ secretion.

Notes: Abstract A laboratory incubation experiment was set up to determine the effects of atrazine herbicide on the size and activity of the soil microbial biomass. This experiment was of a factorial design (0, 5, and 50 μg g−1 soil of non-labelled atrazine and 6.6×103 Bq g−1 soil of 14C-labelled atrazine) x (0, 20, and 100 μg g−1 soil of urea-N) x (pasture or arable soil with a previous history of atrazine application). Microbial biomass, measured by substrate-induced respiration and the fumigation-incubation method, basal respiration, incorporation of 14C into the microbial biomass, degradation of atrazine, and 14C remaining in soil were monitored over 81 days. The amount of microbial biomass was unaffected by atrazine although atrazine caused a significant enhancement of CO2 release in the non-fumigated controls. Generally, the amounts of atrazine incorporated into the microbial biomass were negligible, indicating that microbial incorporation of C from atrazine is not an important mechanism of herbicide breakdown. Depending on the type of soil and the rate of atrazine application, 18–65% of atrazine was degraded by the end of the experiment. Although the pasture soil had twice the amount of microbial biomass as the arable soil, and the addition of urea approximately doubled the microbial biomass, this did not significantly enhance the degradation of atrazine. This suggests that degradation of atrazine is largely independent of the size of the microbial biomass and suggests that other factors (e.g., solubility, chemical hydrolysis) regulate atrazine breakdown. A separate experiment conducted to determine total amounts of 14C-labelled atrazine converted into CO2 by pasture and arable soils showed that less than 25% of the added 14C-labelled atrazine was oxidised to 14CO2 during a 15-week period. The rate of degradation was significantly greater in the arable soil at 24%, compared to 18% in the pasture soil. This indicates that soil microbes with previous exposure to atrazine can degrade the applied atrazine at a faster rate.

Notes: Burst swimming speeds were measured in mackerel 0.275–0.380 m long by filming newly caught fish, first released into a large shore-sited tank, using a high-speed cine camera and real time TV camera. The highest speed was 5.50 m s−1 or 18 body length per second (b.l. s−1) in a 0.305 m long mackerel at 12° C. The recorded maximum tail beat frequency of 18 Hz agrees well with 19 Hz predicted from the measured contraction time of 0.026 s for the anterior lateral swimming muscle. The stride length was close to 1 B.L.; the power, calculated from the drag, was 4.53 W, and, calculated from the muscle used, was 5.07 W; all suggesting that the mackerel is swimming close to its physiological limit.

Notes: Negatively-buoyant Atlantic mackerel, Scomber scombrus L., (fork length 30–39 cm) tilt their bodies with the head up while swimming at speeds below 0.8 body length per second (B.L. s−1). This behaviour is quantitatively described by the body attack angle and swimming speed measured from film records. The maximum recorded body attack angle was 27° in a 32 cm-long fish swimming at 0.45 B.L. s−1 while its nose followed a course close to the horizontal. In general, larger body attack angles were shown at lower swimming speeds and were associated with denser bodies at each speed. We consider that this behaviour pattern allows the fish to maintain a chosen swimming depth while its body creates lift by acting as a hydrofoil. Lift from the fins is insufficient at low swimming speeds.

Notes: The allelopathic influence of four developmental stages of nodding thistle (small rosette, large rosette, bolting and dead plants) on eleven test species (six grasses, four legumes and itself) was investigated using aqueous extract bioassays, aqueous leachate bioassays, and bioassays based on addition of ground material to soil. The aqueous extract and leachate bioassays indicated that nodding thistle was most allelopathic at the rosette stages, while the bioassays involving amendment of soil with thistle tissue showed bolting live and dead plants to be the most allelopathic. It is proposed that nodding thistle is allelopathic at two phases of its development, i.e. at the early bolting stage when the larger rosette leaves are decomposing and releasing soluble inhibitors, and at the stage when bolting plants are dying and releasing insoluble inhibitors. Nodding thistle seedlings appear to be stimulated by addition of thistle tissues to soil, indicating that thistle plants may weaken pasture and simultaneously encourage recruitment of its own species. This is consistent with previous studies detecting high densities of thistle seedlings in the vicinity of deceased parent plants. The six grass species were generally more tolerant to thistle allelopathic effects than were the four legume species, but no consistent differences emerged between different grass or legume species. Influence de l'age de la plante sur le potentiel allélopathique du chardon penche (Carduus nutans L.) vis a vis des prairies de graminées et de légumineusesL'influence allélopathique de 4 stades de développement du chardon penché (petite rosette, grande rosette, montaison, plantes mortes) sur 11 espèces tests (6 graminées, 4 légumineuses et lui-même) a étéétudiée en utilisant des bioessais d'extraction acqueuse, des bioessais de lessivage acqueux et des bioessais fondés sur l'addition au sol d'amendement. Les bioessais d'extraction acqueuse et de lessivage ont montré que le chardon penchéétait plus allélopathique au stade rosette tandis que les bioessais impliquant l'amendement de sol avec des tissues de chardon ont montré que la montaison et les plantes mortes étaient les plus allélopathiques. Il est proposé que le chardon penché est allélopathique à 2 phases de son développement, par exemple au stade montaison précoce quand les plus grandes feuilles de la rosette se décomposent et relachent les inhibiteurs solubles, et au stade où les plantes montées meurent et relächent les inhibiteurs insolubles. Les plantules de chardon penché apparaissent être stimulées par l'addition de tissus de chardon au sol, montrant que les plantes de chardon peuvent affaiblir une prairie et simultanément favoriser sa propre réimplantation. Ceci est conforme avec des études précédentes montrant des fortes densités de plantules de chardon au voisinage de plantes parentes mortes. Les 6 espèces de graminées ont été de façon générale plus tolérantes aux effets allélopathiques que les 4 espèces de légumineuses, mais aucune différence importante ne s'est exprimée entre les différentes espèces de graminées ou de légumineuses. Einfluβ des Pflanzenalters der Nickenden Distel (Carduus nutans L.) auf die allelopathische Wirkung gegen Weidegräser und LeguminosenDie allelopathische Wirkung der Nickenden Distel wurde in 4 Entwicklungsstadien (in kleiner und in voller Rosette, blütentreibend und abgestorben) gegen 11 Pflanzenarten (6 Gräser, 5 Leguminosen und sich selbst) mit wäßrigen Auszügen, Perkolationswasser und Bodenmaterial zum Substrat geprüft. Mit den wäßrigen Auszügen und dem Perkolationswasser zeigte sich die Nickende Distel im Rosetten-Stadium am meisten allelopathisch, während Bodenmaterial mit Resten blütentreibender und abgestorbener Pflanzen wirksamer war. Es kann angenommen werden, daß die Nickende Distel in 2 Entwicklung sphasen allelopathisch wirkt, nämlich wenn die größeren Rosettenblätter oder wenn die blütentreibenden Pflanzen vergeben und 1ösliche Hemmstoffe entlassen. Keimpflanzen der Nickenden Distel werden offensichtlich durch Pflanzenmaterial der Distel im Wachstum angeregt; die Distel schwächt also Weide-Pflanzenarten und fördert zugleich ihre eigene Entwicklung. Dieser Befund deckt sich mit der Beobachtung hoher Keimpflanzen-Dichten um abgestorbenen Mutterpflanzen. Die 6 Gräser waren durchweg gegenüber der allelopathischen Wirkung der Distel unempfindlicher als die 4 Leguminosen, doch innerhalb dieser Gruppen zeigten sich keine klaren Unterschiede.

Notes: Swards of 10 pasture species (six grasses and four legumes) were established and planted with seeds of either of the thistle species Carduus nutans L. or Cirsium vulgare L., and emergence and growth of the thistle seedlings were subsequently monitored. Emergence of C. nutans seedlings was inhibited by ryegrass (Lolium perenne L.) and Yorkshire fog (Holcus lanatus L.) swards, while C, vulgare emergence was inhibited by Yorkshire fog relative to some of the other treatments. Speed of emergence of C. nutans and absolute emergence of C. vulgare seedlings were significantly negatively correlated with pasture cover density, presumably as a consequence of alteration of light quality by the pasture swards. All pasture species inhibited seedling shoot and root growth of both thistle species, although the grasses were the most effective inhibitors. The seedling emergence and growth data for C. nutans in the swards of the 10 species were significantly correlated with the results of a previous study on residual allelopathic effects of the same 10 species on nodding thistle root growth. It is concluded that inhibitory (including allelopathic) influences of pasture species on thistle seedlings have considerable potential as a mechanism for managing problematic thistle populations. Influence de converts de pature de graminees et de legumineuses sur la levée et la croissance de Carduus nutans L. et Cirsium vulgare L.Des couverts de 10 espèces fourrageres (6 graminées et 4 légumineuses) ont étéétablis et infestés avec des graines de 1'une ou 1'autre des espèces de chardon, Carduus nutans L. et Cirsium vulgare L.; la levée et la croissance des plantules de chardon ont été ensuite suivies. La levée des plantules de C. nutans a été inhibéee par les couverts de ray-grass (LoliumperenneL.) et de houlque laineuse (Holcus lanatus L.) tandis que la levée de C. vulgareétait inhibée par la houlque laineuse en comparaison de quelques-unes des autres modalites. La vitesse de levée de C. nutans et la levée globale de C. vulgare ont été corrélées négativement de façon significative avec la densité du couvert, probablement en conséquence de 1'altération de la qualité de la lumière par les tapis, fourragers. Toutes les espèces de fourrages ont inhibé la croissance des tiges et des racines des plantules des 2 espèces de chardon, bien que les graminèes aient été des inhibiteurs plus efficaces. La Ievée des plantules et les chiffres de la croissance de C. nutans dans les couverts des 10 espéces étaient correlées de façon significative avec les résultats d'une étude antérieure sur les effets allélopathiques résiduels de quelques-unes des 10 espèces sur la croissance racinaire du chardon. II est conclu que les effets inhibiteurs (y compris I'allélopathie) des espèces fourragères sur les plantules de chardon ont un potentiel considèrable pour gérer le problème des populations de chardon. Einfluβ von Weidegräser- und Leguminosen-Beständen auf Samenkeimung und Wachstum von Carduus nutans L. und Cirsium vulgare L.In Beständen von 10 Weide-Pflanzenarten (6 Gräser und 4 Leguminosen) wurden Samen der Disteln Carduus nutans L. und Cirsium vulgare L. ausgebracht und deren Keimung und Wachstum beobachtet. Die Keimung von Carduus nutans wurde in Beständen von Weidelgras (Lolium perenne L.) und Wolligem Honiggras (Holcus lanatus L.) gehemmt, während die Keimung von Cirsium vulgare in Wolligem Honiggras genauso wie in einigen anderen Beständen gehemmt war. Die Keimungsgeschwindigkeit von Carduus nutans und die gesamte Keimung von Cirsium vulgäre waren signifikant negativ mit der Dichte der Weide-Pflanzenbestände korreliert, vermutlich wegen Änderung der Lichtqualität durch die Pflanzendecke. Alle Weide-Pflanzenarten, besonders jedoch die Gräser, hemmten das Sproß- und Wurzelwachstum der Keimpflanzen der beiden Disteln. Keimung und Wachstum der Carduus-nutans-Keimpflanzen in den Beständen der 10 Arten entsprachen ganz den Befunden einer früheren Untersuchung über allelopathische Wirkungen derselben 10 Arten auf das Wurzelwachstum der Nickenden Distel. Den Hemmwirkungen (einschließlich allelopathischen) von Weide-Pflanzenarten auf Distel-Keim-pflanzen kommt offenbar eine erhebliche Bedeutung für die Unterdrückung problematischer Distelpopulationen zu.

Notes:   Clusters now form a central element in many regional economic development policies. Location within a cluster of related industries is thought to increase a firm's competitive advantage resulting in higher output and productivity growth rates than in similar firms located beyond the cluster. This study focuses on owner-managers operating small firms within a traditional cluster of metalworking industries and empirically examines the relationship between growth-orientation and the extent and nature of cluster embeddedness. The results indicate only a limited number of differences in growth-orientation given variations in levels of cluster embeddedness. Contrary to conventional wisdom, many of the most growth-oriented entrepreneurs focus their activities outside the cluster, especially in terms of market-based linkages. However, those firms with more advanced process technologies do tend to show above average within cluster linkages.

Notes: After a pretreatment of 2 h exposure to a solution containing 2 × 10−4M ABA, reopening of stomata occurred in epidermal strips of Vicia faba L. cv. Cavalier on an ABA-free incubation solution. After pretreatment with exogenous ABA stomatal apertures were greater when higher levels of KCl were incorporated into the solution used for reopening. Prolonged exposure to exogenous ABA (14 h) did not prevent stomatal reopening upon transfer to ABA-free solutions. However, for both ABA and ABA-free pretreatments, prolonged incubation (1 day after removal of epidermis) resulted in enhanced stomatal apertures when the epidermal strips were exposed to light. This effect was lost 2 days after removal of the epidermis and opening did not occur after 3 days. Epidermal strips containing endogenous ABA were obtained from wilted leaves. Reopening was greatly reduced by the endogenous ABA treatment, and variation of KCl concentration in the incubation solution had little effect on stomatal aperture. It is postulated that during wilting endogenous ABA becomes reversibly bound without loss of activity for a longer period than is obtained using exogenous ABA. The presence of other unidentified compounds may be involved in this process.

Notes: Abstract Acacia suaveolens (Sm.) Willd is a perennial shrub that forms even-aged stands, recruited from a soil seed-bank following fire. It has previously been subject to demographic studies, which used a space-for-time substitution to investigate temporal patterns following fire. In the present study the potential for spatial variation across sites was investigated by sampling at several similarly aged populations in Ku-ring-gai Chase National Park, northern Sydney, Australia. Significant variation in mean size and fecundity of A. suaveolens individuals was observed among sites, over a 2-4.6-fold range in plant size, and a sevenfold range in mean fecundity. The observed variation at 3 years after fire encapsulated most of the variation previously observed among sites 0-17 years since fire, emphasizing the importance of spatial variation in this species. For each site a two-stage (seed, plant) matrix model was constructed, and projected from 3 to 25 years following fire. Population growth was measured as number of seeds per 3-year-old plant, and found to vary 1.4-fold across models for different sites. This site-to-site variation, as well as that in size, fecundity and survival, was statistically significant. Variation in projected seeds per plant could mostly be attributed to differences in fecundity rather than plant survival. Sensitivity analyses emphasized the biological significance of the variation in fecundity. Whereas previous studies have focused on temporal variation, this work demonstrates the importance of extending our understanding of a species to include the spatial component of population dynamics.