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41.
SUMMARY 1. A sampler was developed that displaces surface water which is replaced with water from a sampling tube at a set depth.
2. The displacement sampler is inexpensive, easy to build, and is capable of collecting water at 7.5 I min−1 .
3. Phytoplankton photosynthesis was higher in water from the displacement sampler than in water collected with a Van-Dorn bottle. Subsequent experiments indicated this was due to inhibition caused by the Van-Dorn bottle. 相似文献
2. The displacement sampler is inexpensive, easy to build, and is capable of collecting water at 7.5 I min
3. Phytoplankton photosynthesis was higher in water from the displacement sampler than in water collected with a Van-Dorn bottle. Subsequent experiments indicated this was due to inhibition caused by the Van-Dorn bottle. 相似文献
42.
43.
The growth rate of the indeterminate soybean plant [Glycinemax (L.)Merr.] slows as it proceeds from vegetative phase intoreproductive growth. Yet, the well-nodulated plant acquiresmost of its nitrogen during reproductive growth. Thus, the interrelationshipbetween plant developmental stage and nitrogen fixation wasexamined. It is shown that, regardless of the age of the hydroponicallygrown soybean plant at the time of its inoculation with Bradyrhizobiumjaponicum, the highest rate of nitrogen fixation occurs duringthe pod-filling stage (R5). Nevertheless, maximum total nitrogenfixation is generally achieved when inoculation occurs at thefull-bloom stage (R2). It is shown, however, that flower budsand flowering are not responsible for the enhanced nodulationand nitrogen fixation. Rather, the data suggest that the onsetof rapid nodulation occurs soon after the initiation of thedevelopmentally programmed drop in foliar nitrate reductaseactivity. The ensuing increase in nitrogen fixation providesthe plant with much of its needed nitrogen and hence stimulatesplant mass accumulation during pod-fill. It is suggested thatnitrogen fixation enhances growth of the soybean plant by increasingits net photosynthetic efficiency during reproductive growthand by providing the needed nitrogen at the appropriate timefor maximum seed growth. Key words: Glycine max, nitrate, nitrogen fixation, nodulation 相似文献
44.
Ten to 20% of the net photosynthetic output of a tropical grainlegume may be consumed by the nodulation-nitrogen-fixation process.If plant growth activities during the reproductive phase werelimited by photosynthetic output, enhanced nitrogen fixationwould seemingly lower total plant mass and seed yield. To testthis possibility, soybean [Glycine max (L.) Merr.] plants weregrown hydroponically on nutrient medium supplemented with minimalurea or with an excess of either nitrate or nitrate plus urea.Acetylene reduction activities (i.e. nitrogen fixation rates)and transpiration rates were measured twice weekly on theseplants through pod fill. Of the plants inoculated, those grownon minimal urea revealed significantly greater acetylene reductionactivities and transpiration rates. At maturity, plants thathad fixed nitrogen at a rapid rate during pod fill had a significantlygreater seed size, total plant mass (i.e. net photosyntheticrate) and nitrogen content than uninoculated or poorly nodulatedplants grown on an excess of nitrate. It is concluded, therefore,that a rapid rate of nitrogen fixation during pod fill enhancesboth transpiration and net photosynthetic output. The increasedavailability of usable nitrogen (i.e. ureides), coupled withenhanced transpiration and photosynthetic output, significantlyincreases total plant mass and seed yield. Thus, enhanced nitrogenfixation seems to be an inexpensive means of increasing seedyield of soybean and perhaps of other tropical grain legumes. Key words: Glycine max, nodulation, nitrate, urea 相似文献
45.
GROENHOF ANDREW C.; SMIRNOFF NICHOLAS; BRYANT JOHN A. 《Journal of experimental botany》1988,39(3):353-361
ABSRACT: Groenhof, A. C, Smirnoff, N. and Bryant, J. A. 1988. Enzymicactivities associated with the ability of aerial and submergedforms of Littorella uniflora (L.) Aschers to perform CAM.J.exp. Bot. 39: 353-361. The submerged form of Littorella uniflora shows a full CAM modeof photosynthesis as shown by diel acid fluctuations and elevatedactivities (in comparison to non-submerged leaves) of the enzymesphosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme.Non-submerged plants exhibit no diel fluctuations of acidityand no changes in activity of NADP-malic enzyme or PEPC. PEPCactivity is low and NADP-malic enzyme is not detectable. Furthercharacterization of PEPC extracted from submerged plants duringthe light and dark periods of a diel cycle shows that the enzymeextracted in the dark is more active. In addition, the enzymeshows a decrease in Km (PEP) and an increase in Vmax in thepresence of glucose-6-phosphate, whilst in the presence of malateKm (PEP) is increased and Vmax decreased; this response to malateis only observed in the light and at pH 7.2. Molecular weightdeterminations using a Sephacryl S-300 column show that theenzyme extracted from plants during the dark period has an apparentmol. wt. of 375 KDa and the enzyme extracted from plants duringthe light period has an apparent mol. wt. of 307 KDa. Key words: Littorella uniflora (shoreweed), Crassulacean acid metabolism, PEP carboxylase, malic enzyme 相似文献
46.
ABSTRACT The storage carbohydrate granules from Euglena and Pavlova were compared by light and electron microscopy. Freezeetch studies demonstrated that while both types of granules are crystalline, they have different structures. The elemental microfibril of the euglenoid granule measures 4 nm, and the elemental striation of the granule from Pavlova is 22 nm. The granules each have a unique X-ray diffraction pattern. The storage carbohydrate granules from Pavlova are not the same as paramyton, and the term “paramylon” should be reserved for the euglenoid storage carbohydrate. 相似文献
47.
ABSTRACT. The purpose of this research was to determine whether mice could be protected from lethal challenge with Naegleria fowleri by prior intranasal exposure to pathogenic and nonpathogenic Naegleria. Mortality ranged from 0 to 100% for mice inoculated intranasally (i.n.) with 5 × 103 amebae of 13 human isolates of N. fowleri. Mice were immunized and challenged i.n. using live amebae of strains of low, medium, and high virulence. The greatest protection against lethal challenge was afforded by three immunizing doses of 103 amebae per dose of the strain of medium virulence. Nonpathogenic N. gruberi also was used to immunize mice i.n. against lethal challenge with N. fowleri. Protection was greater following immunization with N. gruberi than it was after immunization with N. fowleri, suggesting that nonpathogenic N. gruberi may be a better immunogen in protecting mice against lethal naeglerial challenge. 相似文献
48.
DICKY S. YU ERIC G. KOKKO JOHN R. BARRON G. BRUCE SCHAALJE BRENT E. GOWEN 《Systematic Entomology》1992,17(4):389-395
Abstract. Image analysis was used to measure the morphological characters of wings of five species of Canadian Itoplectis (Ichneumonidae). The procedure to digitize and measure various elements of the wings with an image analyser is outlined. Specimens were assigned to species by discriminant analysis and independent univariate comparisons of 144 characters from cells, veins and vertices. All the fifty specimens used were assigned to the correct species by both methods. Image analysis of ichneumonid wings is an effective alternative to the conventional identification system. 相似文献
49.
CLARKE ANDREW; LEESON ELSPETH A.; MORRIS G. JOHN 《Journal of experimental botany》1986,37(9):1285-1293
86Rb uptake was examined in two species of unicellular greenalgae, Chlamydomonas nivalis isolated from snow, and a cellwall-less mutant of the temperate freshwater Chlamydomonas reinhardii.In C. reinhardii cells grown at 20°C and cooled rapidlyto 0°C, 86Rb uptake was abolished. Cells cooled rapidlyto 5°C in the absence of ice accumulated 86Rb veryrapidly but the time course of this uptake suggested non-selectiveaccumulation through a damaged plasmalemma. Cells grown at 8°Cwere viable, able to divide and motile; they showed no signsof cold-shock and 86Rb uptake, albeit slow, was measurable at5°C in the absence of extracellular ice. Cells ofC. nivalis grown at 20°C were damaged at sub-zero temperaturesalthough they did show an enhanced 86Rb uptake at 0°C. Cellsgrown at 5°C were able to accumulate 86Rb from media undercooledto -5°C in the absence of extracellular ice, and again showedenhanced uptake at 0°C. The process of acclimation to lowtemperature appears to differ in the two species. Key words: Chlamydomonas, temperature, 86Rb uptake, membrane 相似文献
50.
The xylem vessels of excised adventitious roots of onion, Alliumcepa, were perfused with unbuffered nutrient solution adjustedinitially to either pH 9·3 or 3·9; the pH of thesolution after passage through the xylem, at rates not lessthan 2 xylem volume changes min1, was close to pH 6·5in both instances. The flux of H+ across the xylem/symplastboundary into mildly alkaline, phosphate-buffered solutionsperfusing the vessels could be increased greatly with increasingbuffer strength, up to a maximum value between 0·51·0pmol H+ mm2 s1. The apparent neutralization ofacidic malic acid buffers had a slightly lower maximum capacity,equivalent to 0·3 to 0·5 pmol H+mm2 s1. The addition of 5·0 pmol m3fusicoccin (FC) to the xylem perfusion solution stimulated theentry of H+ into the xylem; in unbuffered perfusion solutionsthe pH fell to pH 3·6 after a lag of 2535 min.FC additions to phosphate-buffered solutions also stimulatedthe H+ flux to an extent similar to that in unbuffered solution,viz. 0·20·4 pmol mm2 s1. The release of K+ (36Rb-labelled) into xylem sap transientlyincreased as the [K+] in weakly buffered perfusion solutionswas raised stepwise; a very marked increase being seen whenthe concentration was raised to 100 mol m3 from 40 molm3. The addition of 5·0 mmol m3 FC to theperfusing solution containing 100 mol m3 K+ rapidly decreasedthe K+ flux to the xylem as the H+ flux increased. Fusicoccinalso inhibited the flux of K+ into unbuffered perfusion solutionsbut the effect appeared reversible. Addition of 10 mmol m3abscisic acid (ABA) to the perfusion solution quickly producedtransient increases in both K+ and H+ fluxes into the xylem.In this and other experiments using weakly phosphate-bufferedperfusing solutions, H+ fluxes were comparable in size to thoseof K+ The results are consistent with the idea that the stele of onionroots contains a proton trarislocating ATPase whose activityresponds to the pH of the xylem sap. It is evident that theactivity of the proton secreting and proton neutralizing mechanismsin the xylem parenchyma control the movement of other ions acrossthe xylem/symplast boundary. Key words: Xylem perfusion, fusicoccin, abscisic acid, pH gradient 相似文献