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991.
The allometry of axis length, diameter, and taper is described for the trunk, rachis, and rachilla of nonbranching ramets of Aralia spinosa. Significant log-linear relationships were found between length and diameter for all axis categories, and in all cases, scaling was negatively allometric. Linear models best described the relationship between length and diameter for the rachis and rachilla, while a quadratic model best described this relationship for the trunk. During the trunk-building stage, the safety factors for trunk height were size dependent, with larger trunks exceeding their predicted critical buckling height. Taper was described by a linear relationship between diameter and position along the axis for all axis categories. All rachises and rachillas sampled exhibited taper along the length of the axis, however, only 51% of the trunks showed continuous taper. The trunk was less tapered than the rachis, but no differences in taper were found between the trunk and the rachilla, or the rachis and the rachilla. In unbranched ramets the large bipinnately compound leaves occupy the space normally occupied by lateral branches. We suggest that the rachis and rachilla are functionally equivalent to branches, that is, acting as axes of exploration and exploitation of the environment. 相似文献
992.
Anna Urbanska W. Freddy Tjallingii Anthony F. G. Dixon Bogumil Leszczynski 《Entomologia Experimentalis et Applicata》1998,86(2):197-203
Sucrose-agarose gels and sucrose liquid diets were used to study the phenol oxidising enzymes in the salivary secretions of the grain aphid, Sitobion avenae (Fabricius). Activity indicating the presence of two oxidoreductases, polyphenol oxidase (PPO) and peroxidase (Px), was found. Both enzymes were present in the aphids stylet sheath (gelling saliva) but only polyphenol oxidase activity was found in the halos around sheaths and thus in watery saliva. Electrical penetration graphs (EPG) revealed that the secretion of these enzymes into the gels, by an individual aphid, was associated with its probing activity observed during penetration of the epidermal and mesophyll tissues. The grain aphids PPO, secreted in its saliva reacted with a range of phenolic compounds. As most of these phenolics occur naturally in cereals, the grain aphid could modify its host-plants phenolic composition. The importance of the grain aphids polyphenol oxidase and peroxidase in detoxifying cereal phenolics is discussed. 相似文献
993.
Amyloidosis is characterized by extracellular deposits of protein fibrils with a high content of β-sheets in secondary structure. The protein forms together with proteoglycans amyloid fibrils causing organ damage and serious morbidity. Intact apolipoprotein A-I (apoA-I) is an important protein in lipid metabolism regulating the synthesis and catabolism of high density lipoproteins (HDL). Usually, apoA-I is not associated with amyloidosis. However, four naturally occuring mutant forms of apoA-I are known so far resulting in amyloidosis. The most important feature of all variants is the very similar formation of N-terminal fragments which were found in the amyloid deposits (residues 1–83 to 1–94). The new insights in the understanding of the association of apoA-I with HDL, its metabolism, and its hypothesized structural findings may explain a common mechanism for the genesis of apoA-I induced amyloidosis. Here we summarized the specific features of all known amyloidogenic variants of apoA-I and speculate about its metabolic pathway, which may have general implications for the metabolism of apoA-I. 相似文献
994.
Seasonal and longitudinal metabolic trends in benthic communities were studied in the five orders of a natural mountain river
(the Stradomka) in southern Poland. The method of oxygen change of rocky substrata in chambers was applied. Metabolic data
were compared with abiotic (light regime, channel geomorphology and stream hydrology), and water chemical variables. A tendency
of downstream increase in gross production and community respiration was observed between 1st and 4th stream orders. The highest
values of GP (0.94 g C m-2 24 h -1) and CR (1.12 g C m-2 24 h -1) were observed in the middle Stradomka course (3–4 orders) in spring. A distinct negative NDM (heterotrophy) of the benthic
community was measured in autumn and spring. During winter NDM was almost constant and oscillated around zero. The P/R ratio
changed according to season and fluctuated between heterotrophy (P/R < 1) and autotrophy (P/R > 1). In general, heterotrophy
prevailed in the study system (except 5th order). A marked shift in P/R between 4th and 5th stream orders confirms the prediction
included in the RCC. Water temperature and PAR accounted for 56% in GP variability, whereas CR and NDM were not related to
these variables. The combined variables (PAR and PO4–P) attributed to 69% in GP variability. The set of chemical factors was less related to Stradomka metabolic data. These results
suggest that metabolic processes in this mountain river remarkably depend on physical variables (solar radiation, altitude,
water temperature and conductivity). Metabolic parameters were similar to other geographical mountain systems.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
995.
The observed endogenous circadian rhythm in plants performing Crassulacean acid metabolism is effected by malate transport
at the tonoplast membrane. Experimental and theoretical work asks for a hysteresis switch, regulating this transport via the
ordering state of the membrane. We apply a schematic molecular model to calculate the thermally averaged order parameter of
the membrane lipid structure in its dependence on external parameters temperature and area per molecule. The model shows a
first order structural phase transition in a biologically relevant temperature range. Osmotic consequences of malate accumulation
can trigger a transition between the two phases by changing the surface area of the cell vacuole. Estimation of the energy
needed to expand the vacuole under turgor pressure because of osmotic changes while acidifying shows that energy needed as
latent heat for the calculated change between phases can easily be afforded by the cell. Thus, malate content and the coexisting
two phases of lipid order, showing hysteretic behavior, can serve as a feedback system in an oscillatory model of Crassulacean
acid metabolism, establishing the circadian clock needed for endogenous rhythmicity.
Received: 2 September 1997/Revised: 24 April 1998 相似文献
996.
997.
Effects of 2-Deoxy-d-Glucose on Methamphetamine-Induced Dopamine and Serotonin Neurotoxicity 总被引:1,自引:0,他引:1
Brian Callahan Jie Yuan Gretchen Stover George Hatzidimitriou George Ricaurte 《Journal of neurochemistry》1998,70(1):190-197
Abstract: The mechanisms underlying the neurotoxic actions of methamphetamine (METH) and related substituted amphetamines are unknown. Previous studies with 2-deoxyglucose (2-DG) have suggested that METH-induced neurotoxicity may involve exhaustion of intracellular energy stores. However, because 2-DG also produces hypothermic effects, and because METH's neurotoxic actions are highly susceptible to thermoregulatory influence, previous findings with 2-DG are difficult to interpret. The present studies were undertaken to further examine the influence of 2-DG's glucoprivic and thermic effects in the context of METH-induced dopamine (DA) and serotonin (5-HT) neurotoxicity. 2-DG protected against METH-induced DA neurotoxicity in both rats and mice. In both species, 2-DG, alone or in combination with METH, produced hypothermic effects. METH's toxic effects on brain 5-HT neurons were either unaffected or exacerbated by 2-DG, depending on species, brain region, and dose of METH tested. These results indicate that different mechanisms may underlie METH-induced DA and 5-HT neurotoxicity, and suggest that, as compared with 5-HT neurons, DA neurons are more susceptible to temperature influence, whereas 5-HT neurons are more vulnerable than DA neurons to metabolic compromise. Additional studies are needed to further assess the role of energy stores in the neurotoxic effects of METH and related drugs. 相似文献
998.
More than a 600-fold variation in nitrogen dioxide assimilation among 217 plant taxa 总被引:4,自引:0,他引:4
H. Morikawa A. Higaki M. Nohno M. Takahashi M. Kamada M. Nakata G. Toyohara Y. Okamura K. Matsui S. Kitani K. Fujita K. Irifune & N. Goshima 《Plant, cell & environment》1998,21(2):180-190
Assimilation of nitrogen dioxide in response to fumigation with 15 N-labelled nitrogen dioxide was studied in 217 plant taxa. The taxa included 50 wild herbaceous plants collected from roadsides (42 genera, 15 families), 60 cultivated herbaceous plants (55 genera, 30 families) and 107 cultivated woody plants (74 genera, 45 families). Two parameters, the 'NO2 -N content', or NO2 -derived reduced nitrogen content in fumigated plant leaves (mg N g–1 dry weight), and the 'NO2 -utilization index', or percentage of the NO2 -derived reduced nitrogen in the total reduced nitrogen, were determined. The NO2 -N content differed 657-fold between the highest ( Eucalyptus viminalis ; 6·57) and lowest ( Tillandsia ionantha and T. caput-medusae ; 0·01) values in the 217 taxa; 62-fold in a family (Theaceae) and 26-fold in a species ( Solidago altissima ). Nine species had NO2 -utilization indices greater than 10%, of which Magnolia kobus , Eucalyptus viminalis , Populus nigra , Nicotiana tabacum and Erechtites hieracifolia had NO2 -N contents > 4·9. These plants can be considered 'NO2 -philic' because in them NO2 -nitrogen has an important function(s). The Compositae and Myrtaceae had high values for both parameters, whereas the monocots and gymnosperms had low ones. These findings suggest that the metabolic pathway of NO2 -nitrogen differs among plant species. The information presented here will be useful for creating a novel vegetation technology to reduce the atmospheric concentration of nitrogen dioxide. 相似文献
999.
Masaki Ishigai Shinichi Arai Yoshihiko Ishitani Kenji Kumaki 《The Journal of steroid biochemistry and molecular biology》1998,66(5-6):281-293
After intravenous administration of the vitamin D3 analog, 22-oxacalcitriol (OCT), to normal rats plasma metabolites were investigated by HPLC, GC-MS and LC-MS. Five side-chain oxidation metabolites, 24R(OH)OCT, 24S(OH)OCT, (25R)-26(OH)OCT, (25S)-26(OH)OCT and 24oxoOCT, were identified by comparison with the corresponding synthetic compounds. These side-chain oxidation metabolites were similar to those of calcitriol [1,25(OH)2 vitamin D3] described previously. Besides these five metabolites, two unique side-chain cleavage metabolites, 20S(OH)-hexanor-OCT and 17,20S(OH)2-hexanor-OCT, were identified as main metabolites in plasma by GC-MS and LC-MS using a specific chemical reaction. Our studies suggest that OCT is extensively metabolized and circulates in blood as a number of metabolites as well as unchanged OCT. This metabolism includes both unique pathways of C23-O22 cleavage and 17-hydroxylation, in addition to the side-chain oxidation metabolites similar to those of 1,25-(OH)2D3. 相似文献
1000.
富勒烯的生物活性研究进展 总被引:6,自引:0,他引:6
90年代初以来,富勒烯类化合物的生物活性逐渐引起人们的注意,初步研究表明在抗艾滋病毒、酶活性抑制、切割DNA、光动力学治疗等方面具有独特的功效.此类化合物在生化、医学、药物学等领域有良好的应用前景. 相似文献