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91.
A NOVEL method for the phosphorylation of sugars by orthophosphate in the presence of cyanogen in dilute aqueous neutral or slightly alkaline solutions has been described, suggesting a plausible model of the prebiotic phosphorylation of sugars1–3. This reaction has now been applied to the synthesis of glucose 1,6-diphosphate, starting either from α-D-glucose 1-phosphate or from D-glucose 6-phosphate. The formation of α-D-glucose 1,6-diphosphate from α-D-glucose 1-phosphate would indicate a possible route for the synthesis of this compound on the primitive Earth. It is known that α-D-glucose 1,6-diphosphate is the coenzyme in the inter-conversion of α-D-glucose 1-phosphate with glucose 6-phosphate catalysed by phosphoglucomutase*. The formation of α-D-glucose 1,6-diphosphate seems to be interesting in view of our model for the chemical evolution of the metabolism of sugars5, as it may connect α-D-glucose 1-phosphate with the glycolytic pathway. 相似文献
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Use of fatty acids for the assessment of zooplankton grazing on bacteria, protozoans and microalgae 总被引:8,自引:1,他引:7
1. The distribution of fatty acids in different groups of bacteria, ciliated protozoans and microalgae is reviewed emphasizing specific fatty acids like odd-branched fatty acids and ( n -3) polyunsaturated fatty acids.
2. Odd-branched fatty acids and ( n -6) fatty acids appear to be good indicators of zooplankton grazing on bacteria and ciliates when they are detected in microcrustacean triacylglycerols. We give several examples where these fatty acids may be used as markers. The value of ( n -3) fatty acids in describing zooplankton grazing on phytoplankton seems to be low. 相似文献
2. Odd-branched fatty acids and ( n -6) fatty acids appear to be good indicators of zooplankton grazing on bacteria and ciliates when they are detected in microcrustacean triacylglycerols. We give several examples where these fatty acids may be used as markers. The value of ( n -3) fatty acids in describing zooplankton grazing on phytoplankton seems to be low. 相似文献
94.
How might wild relatives of modern cereals have responded to past, and how might they respond to future, atmospheric CO2 enrichment under competitive situations in a dry, low‐nutrient environment? In order to test this, Aegilops and Hordeum species, common in semiarid annual grasslands of the Middle East, were grown in nine model ecosystems (400 kg each) with a natural matrix of highly diverse Negev vegetation established on native soil shipped to Basel, Switzerland. In a simulated, seasonally variable climate of the northern Negev, communities experienced a full life‐cycle in 280 (preindustrial), 440 (immediate future) and 600 ppm of CO2 (end of the next century). Neither Aegilops (A. kotschyi and A. peregrina), nor Hordeum spontaneum showed a significant biomass response to CO2 concentrations exceeding 280 ppm The reproductive output remained unaffected or even declined (A. peregrina) under elevated CO2. Non‐structural carbohydrates in leaf tissues increased and N concentration decreased with increasing CO2 concentration. N concentration, germination success and seedling development of newly formed grains were either unchanged or reduced in response to high CO2 treatment of parent plants. In a separate fertilizer × CO2 trial with A. kotschyi nested in smaller model communities, we found no effect of P addition, but a 2–3‐fold biomass increase by NPK addition compared to the unfertilized control. A significant stimulation of biomass by CO2 enrichment (+ 44% between 280 and 600 ppm) was obtained only in the NPK treatment. These data suggest that increased CO2 concentration had little direct effect on growth and reproduction in these ‘wild cereals’ in the recent past, and the same seems to hold for their future, except if N‐rich fertilizer is added. 相似文献
95.
Gert Kwakkel Carel GM Meskers Erwin E van Wegen Guus J Lankhorst Alexander CH Geurts Annet A van Kuijk Eline Lindeman Anne Visser-Meily Erwin de Vlugt J Hans Arendzen 《BMC neurology》2008,8(1):49
Background
Main claims of the literature are that functional recovery of the paretic upper limb is mainly defined within the first month post stroke and that rehabilitation services should preferably be applied intensively and in a task-oriented way within this particular time window. EXplaining PLastICITy after stroke (acronym EXPLICIT-stroke) aims to explore the underlying mechanisms of post stroke upper limb recovery. Two randomized single blinded trials form the core of the programme, investigating the effects of early modified Constraint-Induced Movement Therapy (modified CIMT) and EMG-triggered Neuro-Muscular Stimulation (EMG-NMS) in patients with respectively a favourable or poor probability for recovery of dexterity. 相似文献96.
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Spermatozoa of Bufo bufo japonicus were briefly treated with Triton X-100 to remove their plasma membrane, and were injected into oocytes at various stages of maturation division. All the sperm injected into mature coelomic eggs transformed into pronuclei and synthesized DNA, as a normally fertilizing sperm does. The sperm injected into oocytes at the germinal vesicle (GV) stage did not show any change as long as the GV remained intact. In the oocytes which were induced to mature by progesterone, the injected sperm displayed characteristic features in synchrony with those of the resident female nucleus. These included the formation of several sperm-derived chromosomes in association with multipolar spindles in the oocytes from the stage of the germinal vesicle breakdown to the first polar spindle; the appearance of swollen, vesicular nuclei without concomitant DNA synthesis in those at the stage of the first polar body emission; and the reappearance of the condensed chromosomes with giant spindles in those at the stage of the second meiotic metaphase. Pricking of these last oocytes induced the formation of several male pronuclei and DNA synthesis. These results prove that the injection of detergent-treated sperm employed here provides an excellent means of studying the cytoplasmic state that regulates nuclear behavior. 相似文献
100.
BOBROV ALEXEY V. F. CH.; MELIKIAN ALEXANDER P.; YEMBATUROVA ELENA YU. 《Annals of botany》1999,83(6):601-618
To analyse the status and phylogeny of the genusPhyllocladus,seedsof all seven species of the genus were studied. The complexof features of thePhyllocladusreproductive system point to theisolated position of the genus within the conifers. Relationswith Podocarpaceae s. l., Taxaceae s. l. and Cephalotaxaceaeappeared to be remote because a complex of features clearlydistinguishesPhyllocladusfrom the afore-mentioned taxa. We findit advisable to circumscribe the family Phyllocladaceae as Bessey(1907) did, and place it into the order Taxales Knobl. in Warming(1890). From investigations of the seeds it appears the genusPhyllocladusconsistsof seven species, forming five groups. There is a significanttendency for transformation of the female reproductive structureswithin the generic boundaries ofPhyllocladusseeds, originallysolitary, tending to aggregate in various kinds of compact clusters.Copyright1999 Annals of Botany Company PhyllocladusL. C. & A. Rich, ex Mirb., seed anatomy, seed morphology, systematics, phylogenetic relationships, Phyllocladaceae, Podocarpaceae s. str., Acmopyleaceae, Nageiaceae, Austrotaxaceae, Amentotaxaceae, Torreyaceae, Taxaceae, s. str., Cephalotaxaceae, Taxales. 相似文献