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51.
The microbial metabolism of organic matter (OM) in seagrass beds can create sulfidic conditions detrimental to seagrass growth;
iron (Fe) potentially has ameliorating effects through titration of the sulfides and the precipitation of iron-sulfide minerals
into the sediment. In this study, the biogeochemical effects of Fe availability and its interplay with sulfur and OM on sulfide
toxicity, phosphorous (P) availability, seagrass growth and community structure were tested. The availability of Fe and OM
was manipulated in a 2 × 2 factorial experiment arranged in a Latin square, with four replicates per treatment. The treatments
included the addition of Fe, the addition of OM, the addition of both Fe and OM as well as no addition. The experiment was
conducted in an oligotrophic, iron-deficient seagrass bed. Fe had an 84.5% retention efficiency in the sediments with the
concentration of Fe increasing in the seagrass leaves over the course of the experiment. Porewater chemistry was significantly
altered with a dramatic decrease in sulfide levels in Fe addition plots while sulfide levels increased in the OM addition
treatments. Phosphorus increased in seagrass leaves collected in the Fe addition plots. Decreased sulfide stress was evidenced
by heavier δ34S in leaves and rhizomes from plots to which Fe was added. The OM addition negatively affected seagrass growth but increased
P availability; the reduced sulfide stress in Fe added plots resulted in elevated productivity. Fe availability may be an
important determinant of the impact that OM has on seagrass vitality in carbonate sediments vegetated with seagrasses. 相似文献
52.
Using a combination of a primary growth retardant, mefluidide, a synergistic additive, chlorsulfuron, a detergent to enhance penetration (X-77), and a herbicide, 2,4-D, to provide for control of broadleaf weeds, full-season management of bluegrass (Poa pratensis L.)—tall fescue (Festuca arundinaceae Schreb.) mixtures along roadsides has been achieved. A single spray application is made in the spring, and no additional herbicide applications or mechanical mowing are needed. The treatment is effective with greater than 90% control of fescue seed heads. Those few seed heads that do form remain short. It is economical. The costs of materials and application are equal to or less than the cost of a single mowing cycle. The treatment is environmentally safe when applied in early spring before most agricultural crops have been planted. The effectiveness and low cost of the combination derive from laboratory and greenhouse observations that various materials, herein referred to as additives, often only weakly effective as growth retardants themselves, will interact synergistically with mefluidide to provide overall treatment effectiveness at application rates that are economical. Using this principle, a combination suitable for roadside vegetation management was devised, field-tested for 2 years under actual use conditions, and found to be effective for full-season vegetation management of mixed bluegrass—tall fescue turf to permit considerable cost savings when compared to three-cycle mechanical mowing. 相似文献
53.
Direct evidence is presented for a proline cycle using a cell-free experimental system which sequentially transfers 3H from [1-3H]glucose to NADP+ to Δ1-pyrroline-5-carboxylate and yields [3H]proline. The formation of [3H]proline depends on the presence of NADP, Δ1-pyrroline-5-carboxylate, and the enzymes glucose-6-phosphate dehydrogenase and Δ1-pyrroline-5-carboxylate reductase. The production of [3H]proline from unlabeled proline in the presence of mitochondria provides direct evidence for one complete turn of a proline cycle which transfers reducing equivalents produced by glucose oxidation in the pentose pathway into mitochondria. In this cycle, proline is oxidized to Δ1-pyrroline-5-carboxylate by mitochondrial proline oxidase. Δ1-pyrroline-5-carboxylate is released from mitochondria and is recycled back to proline by Δ1-pyrroline-5-carboxylate reductase with concomitant oxidation of NADPH. At the maximal rate observed, 60% of Δ1-pyrroline-5-carboxylate produced is recycled back to proline. This cycle provides a mechanism for transferring reducing equivalents from NADPH into mitochondria and is linked to glucose oxidation in the pentose pathway by NADPH turnover. 相似文献
54.
55.
Jill S. Marty James P. Higham Elizabeth L. Gadsby Caroline Ross 《International journal of primatology》2009,30(6):807-823
Sexual selection has driven the evolution and elaboration of a wide variety of displays and ornaments in male nonhuman primates,
including capes, cheek flanges, and sexual coloration. Among the most sexually dimorphic of all primates is the drill (Mandrillus leucophaeus), the males of which can be 3 times the mass of females, possess large canines, and exhibit extremely bright sexual skin
coloration. However, the function of male coloration in this species has never been examined. Here, we present data on male
color (measured objectively using digital photography), dominance rank, measures of male-female association, and key sexual
behaviors, of adult male drills (n = 17) living in four semi free-ranging enclosures at the Drill Rehabilitation and Breeding Center in Nigeria. We test the
hypothesis that male coloration is a badge of status, indicating dominance rank, and the hypothesis that male coloration attracts
females. We found that male coloration did indicate rank, and that high ranking, strongly colored males were more likely to
associate with adult females, and more specifically with fully tumescent females. These males also engaged in more sexual
activity. However, measures of male-female association and sexual behaviors were not related to male color once rank had been
taken into consideration; i.e., for males of a given rank, females did not prefer those that were more colorful. We discuss
the results in light of what is known about the wild drill social system, in which unfamiliar individuals may come together
in “supergroups,” and in which quality indicators of competitive ability may be particularly important. 相似文献
56.
Expanded thermal niche for a diving vertebrate: A leatherback turtle diving into near-freezing water
Michael C. James Graeme C. Hays 《Journal of experimental marine biology and ecology》2006,335(2):221-226
The global distribution of extant reptiles is more limited than that of mammals or birds, with low reptilian species diversity at high latitudes. Central to this limited geographical distribution is the ectothermic nature of reptiles, which means that they generally become torpid at cold temperatures. However, here we report the first detailed telemetry from a leatherback turtle (Dermochelys coriacea) diving in cold water at high latitude. An individual equipped with a satellite tag that relayed temperature-depth profiles dived continuously for many weeks into sub-surface waters as cold as 0.4 °C. Global warming will likely increase the foraging range of leatherback turtles further into temperate and boreal waters. 相似文献
57.
James L Weber 《Biology direct》2006,1(1):16-10
Applications of Genome Polymorphism Scans range from the relatively simple such as gender determination and confirmation of
biological relationships, to the relatively complex such as determination of autozygosity and propagation of genetic information
throughout pedigrees. Unlike nearly all other clinical DNA tests, the Scan is a universal test – it covers all people and
all genes. In balance, I argue that the Genome Polymorphism Scan is the most powerful, affordable clinical DNA test available
today. 相似文献
58.
High levels of expression of full length human pro-alpha 2(V) collagen cDNA in pro-alpha 2(V)-deficient hamster cells 总被引:2,自引:0,他引:2
A full length cDNA encoding human pro-alpha 2(V) collagen was constructed. Partial sequencing of the cDNA and primer extension analysis of mRNA from fibroblasts found that pro-alpha 2(V) mRNA differs from the mRNAs of other fibrillar collagens in the increased length of its 5'-untranslated region. The pro-alpha 2(V) cDNA was placed downstream of the human cytomegalovirus immediate early promoter/regulatory sequences for expression studies in cultured Chinese hamster lung cells. These cells have been shown previously to synthesize large quantities of pro-alpha 1(V) homotrimers as their only collagenous product. Transfection resulted in a number of clonal cell lines that express human alpha 2(V) RNA at levels comparable to, and in some cases greater than, levels found in normal human skin fibroblasts. Pro-alpha 2(V) chains produced in the majority of clonal lines were of sufficient quantity to complex all available endogenous pro-alpha 1(V) chains. Chimeric heterotrimers, composed of hamster alpha 1(V) and human alpha 2(V) chains in a 2:1 ratio, were stable to pepsin digestion and were found predominantly associated with the cell layer. Surprisingly, pro-alpha 2(V) chains, in excess to pro-alpha 1(V) chains, were found in the extracellular matrix and, in much greater abundance, in media. These chains were pepsin sensitive, indicating that pro-alpha 2(V) chains can be secreted as nonstable homotrimers or as free chains. 相似文献
59.
One particular kind of structure offers possible explanations, for long-term memory, efficient consolidation of stored information
from the environment, clustering of data strings and multimodal functioning. It is a possible model for pieces of neural structure
and its use offers a uniform method for both studying and constructing an extensive class of mechanisms. 相似文献
60.
Bennett Michael D.; Johnston Spencer; Hodnett George L.; Price H. James 《Annals of botany》2000,85(3):351-357
In 1965 Van't Hof estimated the nuclear DNA amount of an unidentifiedAllium cepa L. cultivar as 2C = 33.55 pg (Experimental CellResearch39: 858). This value has been adopted by commonusage as the main calibration standard for angiosperm DNA C-valueestimations. However, different cultivars have been used whileassuming species DNA C-value constancy. Surprisingly this assumptionhas never been tested. A. cepa is an outbreeder with telomericheterochromatic segments, so intraspecific variation in C-value,possibly correlated with environmental factors as seen in Zeamays L., might be expected. We used laser flow cytometry tocompare nuclear DNA amounts in roots of six A. cepa cultivarsused as calibration standards or from different environments.Tissues from one cultivar, or similar volumes of tissue fromtwo cultivars, were run and the variance between nuclei in 2Cpeaks compared. Only one shoulderless 2C peak was seen for allpairs of co-chopped cultivars. Thus, no large differences inC-value between cultivars from different environments were found.Moreover, comparing cultivars run singly or as pairs showedno evidence for increased variation in 2C peaks in the latter,and hence of critical differences in DNA amounts between AilsaCraig and another cultivar. Such variation was insufficientto make their use as alternative calibration standards, or thepractice of imputing Van't Hof's original C-value estimate tothem, unacceptable for most practical purposes. Given the mechanismsknown which can generate genome size variation, the degree ofconstancy in DNA C-value found seems remarkable. Copyright 2000Annals of Botany Company Allium cepa, onion cultivars, calibration standards, DNA C-value constancy, flow cytometry 相似文献