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1.
The size, shape and number of starch grains have been determinedin mature pepper leaves taken from plants grown under definedconditions of daylength and irradiance. Starch grains were 0.2–7.0 µm diameter and 02–1.5µm in thickness. Grain diameter was positively relatedto daylength and the number of grains per unit leaf area inverselyrelated to daylength. Mean grain diameter was also positivelyrelated to leaf area. Analysis of starch grains from leaves having a wide range ofstarch contents showed that grain diameter was linearly relatedto leaf starch content. However, mean diameter only doubledwith a 10-fold increase in starch content. The number of grainsincreased from approximately 5 ? 1010 m–2 of leaf to over200 ? 1010 m–2 with increasing starch content. The totalsurface area of grains increased from less than 1.0 m2 m–2leaf to over 20 m2 m–2 leaf. Leaf starch grain shape and size are compatible with both efficientstorage as disc-shaped chloroplasts and the maintenance of hightotal grain surface area by increasing grain number more thandiameter. Possible mechanisms for the control of grain initiation,growth and degradation are suggested. Key words: Starch grains, size, shape, pepper leaves  相似文献   
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Vomeronasal/accessory olfactory system and pheromonal recognition   总被引:2,自引:0,他引:2  
Keverne  EB 《Chemical senses》1998,23(4):491-494
Pregnancy block in mice requires exposure of recently mated females tourinary pheromones of a strange male, and when working with inbred strainsthis invariably requires urine from an outbred line. The pheromones whichinduce oestrus and early puberty in mice have been identified as thebrevicomins and dihydrothiazoles. Since the same vomeronasal, neural andneuroendocrine pathways are also activated in pregnancy block, thesecompounds are likely candidates for pregnancy blocking pheromones. However,these relatively simple chemicals lack the capacity to code for differingmouse strains. Since large quantities of the polymorphic major urinaryproteins from the lipocalin family found in urine serve as transporters forthe dihydrothiazoles and brevicomins, and differ across strains, then theseproteins must participate in pheromone recognition in the context ofpregnancy block.  相似文献   
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H2S+ bacteria responsible for the degradation of sulfur-containing amino acids of fish muscle are currently little used to evaluate the microbiological pal quality of fish. Shewanella putrefaciens greatly predominates in this flora, and was therefore used to define a suitable culture method and medium. Inoculations by the Spiral surface method at 25C, with an incubation of 72h, gave the best counts on a medium containing two sources of sulfur (organic and inorganic) for H2S+ bacteria. The culture medium and the NaCl concentration were determinant in the evaluation of this flora. At present there is no standard medium which meets these requirements.  相似文献   
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Dead animal cells stain red in a solution of 20 mg per cent Erythrosin B and as such can be counted on a hemocytometer. This procedure can be used to evaluate the effect of agents on tissue-cultured cells. Many tissue-cultured cells die within a few hours when suspended in a balanced saline solution even though the solution has an osmotic pressure equivalent to serum and is buffered at pH 7.3. This destructive effect cannot be corrected by changing osmotic pressure with sodium chloride. Certain high molecular weight substances that will take up water such as gelatin, blood albumin or 15 centipoise methyl cellulose will completely protect cells when added to a saline solution. The concentration of the agent necessary to exert this effect is of the same order as the concentration of protein in interstitial fluid. Certain kinds of agents capable of exerting oncotic pressure are probably a necessary requirement of fluids surrounding mammalian tissue cells.  相似文献   
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Nine determinate and two indeterminate-bush dry seed cultivars of P. vulgaris were grown in trials for four successive years. Mean annual yield of air dry seed (15% moisture content) varied between 222 and 398 g/m2. Most of the annual variation in yield was accounted for by differences in the quantity of nitrogen fertiliser applied and in the duration of bright sunshine during August. The annual mean harvest date varied between 20 September and 9 October. There was a significant negative correlation between the mean harvest date and the number of Ontario heat units accumulated between 20 May and 20 July. There were significant interactions between genotype and environment for both yield and harvest date; joint regression analysis of the interactions showed that five of the cultivars, which had previously been identified as cold tolerant in laboratory tests, all showed greater stability of yield and of maturity date than standard navy bean types. Environmental variation in the yield components of the cold tolerant selections tended to be compensatory, while that of the standard navy beans was additive in its effects on yield.  相似文献   
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