CO2 uptake by the cultivated hemiepiphytic cactus, Hylocereus undatus

The climate of the native tropical forest habitats of Hylocereus undatus, a hemiepiphytic cactus cultivated in 20 countries for its fruit, can help explain the response of its net CO2 uptake to environmental factors. Under wet conditions, about 85% of the total daily net CO₂ uptake occurs at night via Crassulacean acid metabolism, leading to a high water‐use efficiency. Total daily net CO₂ uptake is reduced 57% by only 10 days of drought, possibly involving stomatal closure induced by abscisic acid produced in the roots, which typically occupy a small substrate volume. Total daily net CO₂ uptake for H. undatus is maximal at day/night air temperatures of 30/20°C, optimal temperatures that are higher than those for desert cacti but representative of ambient temperatures in the tropics; its total daily net CO₂ uptake becomes zero at day/night air temperatures of 42/32°C. Stem damage occurs at 45°C for H. undatus, whose photosynthetic cells show little acclimation to high temperatures compared with other cacti and are also sensitive to low temperatures, ‐1.5°C killing half of these cells. Consistent with its shaded habitat, total daily net CO2 uptake is appreciable at a total daily PPF of only 2 mol m2 day' and is maximal at 20 mol m^?2 day^?1, above which photoinhibition reduces net CO₂ uptake. Net CO₂ uptake ability, which is highly correlated with stem nitrogen and chlorophyll contents, changes only gradually (halftimes of 2–3 months) as the concentration of applied N is changed. Doubling the atmospheric CO₂ concentration raises the total daily net CO₂ uptake of H. undatus by 34% under optimal conditions and by even larger percentages under adverse environmental conditions.     

Criteria for the identification of potential colonizers*

Man's interference with the environment encourages colonization by species that are often undesirable, hence a technique by which potential colonizers can be identified is urgently required. It can be developed when general prerequisites for successful colonization are identified. These prerequisites can then serve as criteria to distinguish potential colonizers from non-colonizers. The proposed relevant prerequisites are associated with two problems encountered by all colonists: small founding populations and a difference in the environmental conditions between the source area and the target, making the target rather unpredictable. Both these features increase the risk of random extinction, which can be overcome by possessing a potential for rapid population growth (high r) and for rapid adaptation to environmental conditions (high genetic variability). The parameters associated with meeting these prerequisites can serve for the identification of potential colonizers and for ranking species as to their colonization ability. The proposed technique may best be tested by comparing the intrinsic growth rate and the electrophoretic variability of species that have recently colonized with closely related species that have not done so under similar circumstances. The colonization of the eastern Mediterranean by Red Sea species immigrating via the Suez Canal created an appropriate system for such a test.     

Schistosoma mansoni: uptake of exogenous hemeproteins by schistosomules grown in vitro

The uptake and fate of the hemeproteins horseradish peroxidase (HRPO) and hemoglobin (Hb) by schistosomules of Schistosoma mansoni maintained in vitro were studied by electron microscopy and cytochemical techniques. After administration of HRPO, reaction product was observed initially in the lumen of the digestive tract, and, after 2 hr of feeding, reaction product was also visible in the cytoplasm of the gastrodermis. There was no evidence of pinocytosis. After administration of Hb, reaction product was observed only in the lumen of the digestive tract. As is found following red blood cell feeding, digestive pigment was formed in the lumen of the gut following Hb feeding. The possible significance of these findings is discussed.     

Effect of papaya (Carica papaya) leaf extract as dietary growth promoter supplement in red hybrid tilapia (Oreochromis mossambicus × Oreochromis niloticus) diet

The purpose of this experiment was to examine the potential use of Carica papaya leaf extract as a supplement to promote growth and improve feed utilization in red hybrid tilapia. Five diets were formulated containing isolipidic (80 g/kg) and isonitrogenic (350 g/kg) levels. All feeds contained similar types and amounts of raw materials but differed in the inclusion of papaya leaf extract (0, 5, 10, 20 and 40 g/kg feed). The initial size of fish used was 2.3 ± 0.01 g. Each diet was performed in triplicate tanks, and the feeding period was 12 weeks. Fish fed diet containing 2% papaya leaf extract (PLE) had the highest final weight, 31.14 ± 1.47 g, followed by 1% PLE (27.27 ± 1.75 g). These two diets (1% and 2%) were also showed significant improvements of weight gain, SGR, and feed efficiency of the red hybrid tilapia (p < 0.05). However, papaya leaf extract did not affect the HSI, VSI, PER, digestive enzymes activity, blood composition, and survival rate. Supplementing the diets with papaya leaf extract lowered serum urea. Findings of this research suggest that adding papaya leaf extract to the diet of red hybrid tilapia improves growth and feed efficiency without adversely affecting blood parameters. Therefore, an inclusion level between 1% and 2% of the papaya leaf extract is recommended as a feed additive to promote red hybrid tilapia fry growth.     

A trace fossil assemblage from fluvial Old Red deposits (Wood Bay Formation; Lower to Middle Devonian) of NW-Spitsbergen, Svalbard

From the fluvial Old Red Sandstone (ORS) of the Lower to Middle Devonian Wood Bay Formation (NW-Spitsbergen), a diverse trace fossil assemblage, including two new ichnotaxa, is described: Svalbardichnus trilobus igen. n., isp. n. is interpreted as the three-lobed resting trace of an early phyllocarid crustacean (Rhinocarididae). Cruziana polaris isp. n. yields morphological details that point towards a trilobite origin. This occurence of presumably marine trace makers in a fluvial red bed sequence raises the question of whether we are dealing with marine ingressions that are not sedimentologically expressed, with homeomorphy, or with an adaptation of marine groups to non-marine environments.     

Characterization of the growth and lipid content of the diatom Chaetoceros muelleri

Chaetoceros muelleri (Schütt) was cultured on a thermal gradient plate, subjected to two media types with a range of specific conductances, and evaluated for growth and neutral lipid accumulation. Growth was measured directly by daily changes in cell numbers and indirectly by changes in optical density at 750 nm. C. muelleri exhibited a growth rate of at least two doublings day-1 over broad temperature (20 to 35 °C) and conductance ranges (10 to over 60 mS cm-1) and the optimum growth rate approached 4.0 doublings day-1 at 30 °C and a conductance of 25 mS cm-1. Intracellular neutral lipid storage was evaluated with fluorometry and epifluorescent microscopy using the fluorochrome Nile Red. Gravimetric analysis revealed a total lipid content in nitrogen-depleted cultures of C. muelleri of over 400 mg L-1, five to seven times that observed in nitrogen-replete cultures. Based on its high growth rate, tolerance to a broad range of temperatures and specific conductances, and large quantity of intracellular lipid, C. muelleri may have potential for exploitation as a renewable precursor to liquid fuels or as a lipid source. This revised version was published online in August 2006 with corrections to the Cover Date.     

应用基因敲除快速构建大肠杆菌突变体改造脂肪酸代谢途径

【目的】基因敲除技术是研究基因功能的重要手段。我们试图建立一种快速、高效的大肠杆菌基因敲除方法。【方法】利用大肠杆菌(Escherichia coli)BW25113单基因缺失体Keio文库,将经典的Red同源重组技术与P1噬菌体转导技术相结合,对E.coli MG1655脂肪酸代谢基因进行快速敲除。【结果】获得了大肠杆菌β-氧化途径的缺失菌株△fadD、△fadE和△fadD-△fadE;脂肪酸合成途径缺失菌株△fabH、△fabF和△fabH-△fabF。敲除fadD和fadE对生长情况没有影响;敲除fabH后,生长速度明显减慢;敲除fabF对生长几乎没有影响。FadD、FadE及双敲缺失体的脂肪酸含量18.2 mg/L、20.0mg/L和19.2 mg/L,略高于野生型17.5 mg/L;FabH、FabF及双敲缺失体的含量分别为12.6 mg/L、15.2 mg/L和11.2 mg/L,明显低于野生型。【结论】在单基因突变体文库基础上,利用P1噬菌体转导、Red同源重组和抗性基因消除进行基因敲除,简化了构建大肠杆菌单基因和多重突变体的方法。     

Habitat richness affects home range size in the red fox Vulpes vulpes

The spatial behaviour of the red fox Vulpes vulpes shows a great flexibility (Voigt and Macdonald, 1984). Home range size varies from 10 to over 5000 ha (Macdonald, 1987; Voigt, 1987). In carnivores, variations in home range size, weighed for body mass (Gittleman and Harvey, 1982), are largely related to differences in habitat productivity, but the intraspecific local variation in home range size can be only partially explained by differences in productivity. Macdonald (1981, 1983) suggested that home range size and configuration were determined in the red fox by the dispersion of food-rich patches. More recently, it has been found that

1.

(a) where humans are intolerant to the fox, resting sites are often located peripherally in home ranges (Meia and Weber, 1993);