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31.
Faustino Menegus Liliana Cattaruzza Leonardo Scaglioni Enzio Ragg 《Physiologia plantarum》1992,86(1):168-172
Seeds of the water plant Trapa natans L. (water chestnut) can germinate in strict anoxia. The seedlings show seminal roots growing upwards while shoot buds remain quiescent until O2 becomes available. Trapa seedlings are highly tolerant to anoxia. The rate of ethanol fermentation was 21.2 μmol (g FW)−1 h−1 , while production of lactate was negligible and lower than that of succinate. The seminal root of Trapa compares better to the rice coleoptile rather than to the rice root, both functionally and as to the metabolic response to anoxia. The anaerobic germination of Nuphar luteum L. and Scirpus mucronatus L. was also characterized by a limited developmental program. 相似文献
32.
The influence of temperature on the biochemical composition of eight species of marine phytoplankton was investigated. Thalassiosira pseudonana Hasle and Heim-dal, Phaeodactylum tricornutum Bohlin and, Pavlova lutheri Droop (three of eight species studied) had minimum values of carbon and nitrogen quotas at intermediate temperatures resulting in a broad U-shaped response in quotas over the temperature range of 10 to 25°C. Protein per cell also had minimum values at intermediate temperatures for six species. For T. pseudonana, P. tricornutum, and P. lutheri, patterns of variation in carbon, nitrogen, and protein quotas as a function of temperature were similar. Over all species, lipid and carbohydrate per cell showed no consistent trends with temperature. Only chlorophyll a quotas and the carbon: chlorophyll a ratios (θ) showed consistent trends across all species. Chlorophyll a quotas were always lower at 10°C than at 25°C. Carbon: chlorophyll a ratios (θ) were always higher at 10°C than at 25°C. We suggest that although θ consistently increases at lower temperatures, the relationship between temperature and θ ranges from linear to exponential and is species specific. Accordingly, the interspecific variance in θ that results from species showing a range of possible responses to temperature increases as temperature declines and reaches a maximum at low temperatures. High photon flux densities appear to increase the potential interspecific variance in the carbon: chlorophyll a ratio and therefore exacerbate these trends. 相似文献
33.
The enzyme activity of ribulose 1, 5-bisphosphate carboxylase-oxygenase (RuBisCO) and phosphoenolpyruvate carboxylase (PEPC) was measured in four species of marine benthic diatoms isolated from subtidal sediments of Graveline Bayou, Mississippi. Enzyme activities were measured in cultures of Amphora micrometra Giffen, A. tenerrima Aleem and Hustedt, Nitzschia fontifuga Cholnoky, and Nitzschia vermicularis Grunow that were grown at light levels supporting μmax and at light-limiting irradiances. All four species exhibited similar RuBisCO: PEP ratios (range = 1–1.8) at μmax the lowest ratio (0.4) was observed in A. micrometra. Reduced light levels increased PEPC relative to that measured at μmax in two species. Two-dimensional paper chromatography was used to determine the first products of carbon fixation in A. micrometra After a 15 s incorporation period, the first product of photosynthetic carbon fixation was 3-phosphoglycerate even though this alga had a PEPC activity that was three times higher than that of RuBisCO. After 30 s, over 50% of the recovered radioactivity was still in this compound. Stable carbon isotope analyses of a mixture of the four pennate diatoms also suggest the predominant carbon fixation pathway in these benthic diatoms was similar to C3 plants. 相似文献
34.
W. B. Curry M. D. Grabe I. V. Kurnikov S. S. Skourtis D. N. Beratan J. J. Regan A. J. A. Aquino P. Beroza J. N. Onuchic 《Journal of bioenergetics and biomembranes》1995,27(3):285-293
The simplest views of long-range electron transfer utilize flat one-dimensional barrier tunneling models, neglecting structural details of the protein medium. The pathway model of protein electron transfer reintroduces structure by distinguishing between covalent bonds, hydrogen bonds, and van der Waals contacts. These three kinds of interactions in a tunneling pathway each have distinctive decay factors associated with them. The distribution and arrangement of these bonded and nonbonded contacts in a folded protein varies tremendously between structures, adding a richness to the tunneling problem that is absent in simpler views. We review the pathway model and the predictions that it makes for protein electron transfer rates in small proteins, docked proteins, and the photosynthetic reactions center. We also review the formulation of the protein electron transfer problem as an effective two-level system. New multi-pathway approaches and improved electronic Hamiltonians are described briefly as well. 相似文献
35.
Martin Sprung 《Hydrobiologia》1995,304(2):117-132
Shell growth of tagged zebra mussels (Dreissena polymorpha) was monitored in lakes at 3 sites over 1 1/2 years. It varied greatly with the season and was almost absent during winter
months. Shell growth was significantly correlated with seston concentration, but not with water temperature. The theoretical
maximum size (L∞) of the v. Bertalanffy growth equation did not vary seasonally.
Tissue weight underwent a pronounced seasonal cycle. In animals of 20 mm shell length, minimum weights recorded in September
only corresponded to one quarter to one third of the maxima in late spring. Tissue weight of animals from the 3 sites was
distinctly different.
Carbohydrate content of the tissue stayed below 10 per cent and tended to be highest in spring. Spring maxima of lipids were
very pronounced. These lipids were primarily located in the digestive gland.
These data were combined with data of gonad size by Borcherding (1991). Results imply that production of reproductive tissue
even continues at a retarded rate during winter months, if food conditions were favourable. With poor food conditions, no
production of reproductive tissue was estimated during winter; this, however, was followed by an elevated rate of reproductive
tissue production in spring. Weight specific production decreased with a weight exponent of −0.24. Shell and byssus production
contributed only in the range of 10 per cent to total production.
Reproductive effort showed maxima of 30 to 45%. It increased with shell length at 2 sites and decreased at the other site
with the largest animals. 相似文献
36.
E. E. Hiatt L. Georgi S. Huston D. C. Harshman S. A. Lewis A. G. Abbott 《Journal of nematology》1995,27(2):143-152
The genetic heterogeneity of two M. arenaria race 2 populations (designated Pelion and Govan) was examined using RFLP analysis of 12 clonal lines established from single egg masses (six distinct clonal lines from each population). These populations are essentially identical by traditional biochemical and race identification schemes; however, the Govan population is more aggressive than the Pelion population, producing larger galls and exhibiting greater reproductive capabilities on many soybean cultivars and experimental accessions. Variation at the genomic DNA level was examined using probes representative of expressed DNA sequences present in the eukaryotic genome. Ribosomal DNA, interspersed repeated sequences, and cDNA probes were tested for detection of polymorphism within and between single egg mass lines of each population. Cloned cDNAs and ribosomal intergenic spacer sequences detect polymorphism both within and between populations, demonstrating the usefulness of these sequence classes for molecular genetic analysis of population structure and genome evolution. 相似文献
37.
C. G. McDonald C. W. Hawryshyn 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1995,176(2):255-260
To examine the influence of the spectral characteristics of underwater light on spectral sensitivity of the ON and OFF visual pathways, compound action potential recordings were made from retinal ganglion cells of threespine stickleback from different photic regimes. In fish from a red-shifted photic regime (P50 680 nm for downwelling light at 1m), peak sensitivity of both the ON and OFF pathways was limited to long wavelength light (max 600–620). In contrast, the ON pathway of fish from a comparatively blue-shifted (P50 566 nm) photic regime exhibited sensitivity to medium (max 540–560) and long (max 600 nm) wavelengths, while the OFF pathway exhibited peak sensitivity to only medium (max 540 nm) wavelength light. In a third population, where the the ambient light is moderately red-shifted (P50 629 nm), the ON pathway once again exhibited only a long wavelength sensitivity peak at 620 nm, while the OFF pathway exhibited sensitivity to both medium (max 560 nm) and long (max 600–620 nm) wavelength light. These findings suggest that the photic environment plays an integral role in shaping spectral sensitivity of the ON and OFF pathways. 相似文献
38.
人脑神经元特异性烯醇化酶的纯化方法 总被引:1,自引:0,他引:1
采用改良的Grace层析方法,经一次DEAE-Sephadex A50柱层析即从人脑中纯化了神经元特异性烯醇化酶,比活力为92.1U/mg,纯化倍数为59.4.该酶纯化后,经SDS-聚丙烯酰胺凝胶电泳鉴定为单一蛋白质谱带.此外,还测定了其部分理化性质,其亚单位分子量为45000,等电点pI为4.7,氨基酸组成分析表明其为一种酸性蛋白质;对2-磷酸甘油酸的Km值为5.6×10-4mol/L. 相似文献
39.
Summary Recent availability of stable and well characterized selectable markers and ability to combine alien genomes parasexually have contributed to the development of molecular biology in higher plants, including gene expression and genetic manipulation.Several types of biochemical mutants (resistant to inhibitory concentrations of aminoacid(s) or aminoacid analogs as well as deficient for enzyme activity) have recently been isolated and characterized biochemically and genetically. Among them, mutants with alterations in the nitrogen and aminoacid metabolism, or in the activity of alcohol dehydrogenases are being used in the development of more efficient techniques of gene transfer.The manipulation of whole genomes by sexual or somatic cell fusion offers new potential in this field, but refinement of transfer techniques is desirable. The new set of selectable markers obtained through advanced cellular technology, as well as our ability to regenerate plants from manipulated cell lines are expected to play a major role in cellular engineering. 相似文献
40.
John M. Brand 《Biochemical Systematics and Ecology》1978,6(4):337-340
Studies on the chemistry of the 2,6-dialkylpiperidines in the venom of various fire ant species have shown that these alkaloids have practical value as chemotaxonomic characters. In addition, the finding that variations exist in the distribution of the geometric isomers between species and castes has led to a hypothetical construct for the biochemical evolution of these compounds. These various results, obtained previously, are integrated here as a coherent whole. 相似文献