Impact on growth and aflatoxin B1 accumulation by Kluyveromyces isolates at different water activity conditions

This study showed the impact on germination, mycelial growth and aflatoxin B₁ accumulation when interacting Aspergillus aflatoxigenic strains with Kluyveromyces isolates and the effect of water activity on this relationship. Isolates Y₁₄ and Y₁₆ reduced the percentage of germination of all Aspergillus strains and decrease germ tube elongation rate at majority of water activity assayed. Similarly they produced an increase of germination lag phase and lag phase of growth beside decreased growth rate of all Aspergillus strains. At water activities 0.994, 0.982, 0.955 and 0.937, no aflatoxins were produced in paired cultures with isolates Y_25, Y₂₂, Y₁₆, and Y₁₄, and Kluyveromyces isolates Y₁₄ and Y₁₆ impact both growth and aflatoxin accumulation at wide range of water activity.     

Evolutionary trends of the hairy-faceSaguinus in terms of the dental and cranial morphology

Shape variations in the dentition and the cranium were analyzed for sevenSaguinus forms of the hairy-face tamarin by applying the factor analysis method. The results obtained for the dental and cranial measurements were almost consistent with each other. The magnitude of the difference in shape factors between theS. nigricollis group and theS. midas group is appreciably larger than that between the former group and theS. mystax group. If the ancestral geographic centre of origin is postulated as being within the region which is inhabited by the livingS. nigricollis group, the morphological distances between any pairs of groups correlate well with the geographic distances between them. Concerning the dental and cranial morphologies, the physical changes in the three species group probably took place in two directions; that is, from theS. nigricollis group to theS. mystax group, and from theS. nigricollis group to theS. midas group. The forms belonging to each species group are more closely related to each other, with the exception ofS. imperator in theS. mystax group. The uniqueness ofS. imperator was clearly demonstrated by factor analysis and distance analysis. In theS. mystax group, although still hypothetical,S. imperator may have been related only through the basic ancestral stock toS. labiatus andS. mystax.     

Edaphic and Floristic Variation within a 1‐ha Plot of Lowland Amazonian Rain Forest1

Several studies in lowland tropical rain forests have documented effects of local‐scale topographic variation on plant species distribution and abundance patterns. Few studies have compared the distribution patterns of more than one plant group, however, and even fewer have related these to measured physical and chemical soil characteristics. Here, we document such soil characteristics within a square 1‐ha plot in Amazonian Ecuador, and compare them to the distribution patterns of terrestrial pteridophytes, angiosperm ground herbs, and palms. Substantial variation in soil properties was found within the plot. The three plant groups showed highly correlated floristic patterns within the 1‐ha plot even after the effect of geographical distances had been taken into account. Mantel tests yielded significant correlations between edaphic patterns, as measured by distances in various soil and topographic characteristics, and floristic patterns. For all three plant groups, differences in elevation within the plot were highly correlated with floristic distances, and for terrestrial pteridophytes and palms, distances in soil calcium content and sand content were also important. Our results resembled those obtained at wider spatial scales with the same plant groups, which indicates that soil factors may play an important role for distribution and beta diversity of plants, even at the local scale.     

3种桉树组培苗不定根发生发育过程的解剖学观察

以巨尾桉‘GL9’、尾巨桉‘DH32-29’和尾边桉‘XF35’3种桉树无性系组培生根苗为材料,采用常规石蜡切片技术,对石蜡切片制作过程中的固定环节进行了优化,观察了桉树不定根的发育过程。结果表明:(1)采用FAA固定液固定材料,可获得染色清晰,组织完整的桉树根系切片。(2)‘GL9’和‘DH32-29’在生根诱导8d后生出不定根,生根类型为皮部生根;‘XF35’在生根诱导12d后生出不定根,生根类型为愈伤组织生根;‘GL9’不定根的根尖和根基处均有细胞旺盛分裂,‘DH32-29’不定根只在根尖有细胞旺盛分裂,‘XF35’不定根则只在其根基处有大量旺盛分裂的细胞。     

Ca-ATPase activity and protein composition of sarcoplasmic reticulum membranes isolated from skeletal muscles of typical hibernator,the ground squirrel Spermophilus undulatus

Ca-ATPase activity in sarcoplasmic reticulum (SR) membranes isolated from skeletal muscles of the typical hibernator, the ground squirrel Spermophilus undulatus, is about 2-fold lower than that in SR membranes of rats and rabbits and is further decreased 2-fold during hibernation. The use of carbocyanine anionic dye Stains-All has revealed that Ca-binding proteins of SR membranes, histidine-rich Ca-binding protein and sarcalumenin, in ground squirrel, rat, and rabbit SR have different electrophoretic mobility corresponding to apparent molecular masses 165, 155, and 170 kDa and 130, 145, and 160 kDa, respectively; the electrophoretic mobility of calsequestrin (63 kDa) is the same in all preparations. The content of these Ca-binding proteins in SR membranes of the ground squirrels is decreased 3–4 fold and the content of 55, 30, and 22 kDa proteins is significantly increased during hibernation.     

Sedimentation and pedogenesis in a Central Amazonian Black water basin

Sedimentation rates were estimated in a Central Amazonian Black-water inundation forest. Sediment deposition on the forest ground, remote from the river bed, during an annual flood period, is of the order of 1 to 10 tons per hectare, depending on water depth and duration of flooding. The sediments consisted of fine organic matter, kaolinite, quartz sands and biogenic particles of silica. Their genesis and deposition depend on the interplay between pedogenic, limnological and biological processes. Sediments derive primarily from the materials leached from the soils. Clay soils are the main source of dissolved silica, and the sandy soils are the main sources of organic coumpounds and mineral particles. The physical sedimentation of particles as quartz sand grains only occurs in the upper reaches of the studied river. In the flood plain, the sedimentation is due to the coagulation and deposition of combined mineral particles and humic substances, and to the biological precipitation of the silica leached from the soil by sponges.     

Nitrate depletion in the riparian zone of a small woodland stream

Field enrichments with nitrate in two spring-fed drainage lines within the riparian zone of a small woodland stream near Toronto, Ontario showed an absence of nitrate depletion. Laboratory experiments with riparian substrates overlain with nitrate enriched solutions revealed a loss of only 5–8% of the nitrate during 48 h incubation at 12°C. However, 22–24% of the initial nitrate was depleted between 24 and 48 h when a second set of substrate cores was incubated at 20°C. Short-term (3 h) incubations of fresh substrates amended with acetylene were used to estimate in situ denitrification potentials which varied from 0.05–3.19 g N g^–1 d^–1 for organic and sandy sediments. Denitrification potentials were highly correlated with initial nitrate content of substrate samples implying that low nitrate levels in ground water and riparian substrates may be an important factor in controlling denitrification rates. The efficiency of nitrate removal in spring-fed drainage lines is also limited by short water residence times of < 1 h within the riparian zone. These data suggest that routes of ground water movement and substrate characteristics are important in determining nitrate depletion within stream riparian areas.     

Contamination of Groundnut in South‐Western Nigeria by Aflatoxigenic Fungi and Aflatoxins in Relation to Processing

Groundnut is commonly consumed in its roasted form by many Nigerians. This study was therefore conducted to determine the levels of aflatoxin in roasted groundnut retailed in south‐western Nigeria with a view to assessing the fitness of the processed nut for human consumption. The effects of roasting and de‐coating as alternative methods for reducing the ‘aflatoxin scare’ in the nut were further assessed on aflatoxigenic fungal load and aflatoxin content of the nuts. Forty‐eight samples of retailed raw and roasted groundnut were collected and assessed by mycological and thin‐layer chromatographic analysis for changes in aflatoxigenic fungal population and aflatoxin concentration, respectively. Consequently, 480 isolates of the Aspergillus section Flavi group, A. flavus L strain (n = 410), A. tamarii (n = 56), A. parasiticus (n = 7) and A. parvisclerotigenus (n = 7), were recovered from all samples. Aflatoxigenic isolates of A. flavus L strain (58.8%) had a significantly (P < 0.05) higher incidence than the non‐aflatoxigenic isolates (41.2%). Aflatoxins were detected in 43 (89.6%) of the samples. Approximately 25% of all samples exceeded the 20 ng/g limit for aflatoxin B₁ (AFB₁) adopted by the National Agency for Food and Drug Administration and Control while 83 and 79% of all samples contained AFB₁ and total aflatoxins above the European Union limits of 2 and 4 ng/g, respectively. Aflatoxin concentrations in the raw and coated samples were as much as five times higher than those in the roasted and de‐coated nuts, respectively. However, no significant difference was recorded between aflatoxin levels in the coated and de‐coated samples. This study has shown that roasting of groundnut and testa removal (de‐coating) are effective processing interventions that can significantly lower aflatoxin quantities in the kernels, thus making it fit for human consumption.     

Age-dependent use of local and global landmarks during escape: experiments using Columbian ground squirrels

How animals utilize their space often changes during ontogeny, perhaps resulting from alternative use of orientation mechanisms. This study investigated whether landmark-based navigation mechanisms were age-dependent in Columbian ground squirrels (Spermophilus columbianus). In field tests, young (1-2 years old) and adult (3-6 years old) animals had to find an escape burrow when either local, global, or both types of landmarks were obstructed. The comparison of escape times between age groups revealed that adult squirrels found escape burrow faster than young animals if global landmarks were available. However, if only local landmarks were present, young squirrels outperformed older animals. The comparison of escape time within each age group showed that obstruction of global or local landmarks lengthened escape time of adult squirrels. In contrast, young animals had longer escapes only when local landmarks were obstructed. The results suggested that the use of different types of landmarks was age specific.