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71.
72.
Paul Dijkstra AD. H. M. C. Schapendonk KO. Groenwold Marinus Jansen Siebe C. Van De Geijn 《Global Change Biology》1999,5(5):563-576
Winter wheat was grown at ambient and elevated (ambient plus 350 μL L–1) CO2 concentrations in open top chambers and in field-tracking sun-lit climatized enclosures (elevated is 718 μL L–1). There was no significant effect of CO2 concentration on sheath, leaf and root biomass and leaf area in the early spring (January to April). 24-h canopy CO2 exchange rate (CCER) was not significantly affected either. However, elevated CO2 concentration increased CCER at midday, decreased evapotranspiration rate and increased instantaneous water-use-efficiency during early spring. Leaf, sheath and root nitrogen concentration per unit dry weight decreased and nonstructural carbohydrate concentration increased under elevated CO2, and N-uptake per unit ground area decreased significantly (– 22%) towards the end of this period. These results contrast with results from the final harvest, when grain yield and biomass were increased by 19% under elevated CO2. N concentration per dry weight was reduced by 5%, but N-uptake per unit ground area was significantly higher (+ 11%) for the elevated CO2 treatment. 24-h and midday-CCER increased significantly more in late spring (period of 21 April to 30 May) (respectively by + 40% and 53%) than in the early spring (respectively 5% and 19%) in response to elevated CO2. Midday evapotranspiration rate was reduced less by elevated CO2 in the late spring (– 13%) than in early spring (– 21%). The CO2 response of midday and 24-h CCER decreased again (+ 27% and + 23% resp.) towards the end of the growing season. We conclude that the low response to CO2 concentration during the early spring was associated with a growth-restriction, caused by low temperature and irradiance levels. The reduction of nitrogen concentration, the increase of nonstructural carbohydrate, and the lower evapotranspiration indicated that CO2 did have an effect towards the end of early spring, but not on biomass accumulation. Regression analysis showed that both irradiance and temperature affected the response to CO2. 相似文献
73.
Ca2+, annexins, and GTP modulate exocytosis from maize root cap protoplasts 总被引:3,自引:0,他引:3 下载免费PDF全文
Protoplasts isolated from root cap cells of maize were shown to secrete fucose-rich polysaccharides and were used in a patch-clamp study to monitor changes in whole-cell capacitance. Ca2+ was required for exocytosis, which was measured as an increase in cell capacitance during intracellular dialysis with Ca2+ buffers via the patch pipette. Exocytosis was stimulated significantly by small increases above normal resting [Ca2+]. In the absence of Ca2+, protoplasts decreased in size. In situ hybridization showed significant expression of the maize annexin p35 in root cap cells, differ-entiating vascular tissue, and elongating cells. Dialysis of protoplasts with maize annexins stimulated exocytosis at physiological [Ca2+], and this could be blocked by dialysis with antibodies specific to maize annexins. Dialysis with milli-molar concentrations of GTP strongly inhibited exocytosis, causing protoplasts to decrease in size. GTPgammaS and GDPbetaS both caused only a slight inhibition of exocytosis at physiological Ca2+. Protoplasts were shown to internalize plasma membrane actively. The results are discussed in relation to the regulation of exocytosis in what is usually considered to be a constitutively secreting system; they provide direct evidence for a role of annexins in exocytosis in plant cells. 相似文献
74.
CEES GRASHOFF † PAUL DIJKSTRA † SANDERINE NONHEBEL ‡ AD H.C.M. SCHAPENDONK† SIEBE C. VAN DE GEIJN† 《Global Change Biology》1995,1(6):417-428
The effect of elevated [CO2] on the productivity of spring wheat, winter wheat and faba bean was studied in experiments in climatized crop enclosures in the Wageningen Rhizolab in 1991–93. Simulation models for crop growth were used to explore possible causes for the observed differences in the CO2 response. Measurements of the canopy gas exchange (CO2 and water vapour) were made continuously from emergence until harvest. At an external [CO2] of 700 μmol mol?1 Maximum Canopy CO2 Exchange Rate (CCERmax) at canopy closure was stimulated by 51% for spring wheat and by 71% for faba bean. At the end of the growing season, above ground biomass increase at 700 μmol mol?1 was 58% (faba bean), 35% (spring wheat) and 19% (winter wheat) and the harvest index did not change. For model exploration, weather data sets for the period 1975-88 and 1991–93 were used, assuming adequate water supply and [CO2] at 350 and 700 μmol mol?1. For spring wheat the simulated responses (35–50%) were at the upper end of the experimental results. In agreement with experiments, simulations showed smaller responses for winter wheat and larger responses for faba bean. Further model explorations showed that this differential effect in the CO2 response may not be primarily due to fundamental physiological differences between the crops, but may be at least partly due to differences in the daily air temperatures during comparable stages of growth of these crops. Simulations also showed that variations between years in CO2 response can be largely explained by differences in weather conditions (especially temperature) between growing seasons. 相似文献
75.
Nadezhda E. Yun Shannon Ronca Atsushi Tamura Takaaki Koma Alexey V. Seregin Kelly T. Dineley Milagros Miller Rebecca Cook Naoki Shimizu Aida G. Walker Jeanon N. Smith Joseph N. Fair Nadia Wauquier Bayon Bockarie Sheik Humarr Khan Tomoko Makishima Slobodan Paessler 《Journal of virology》2016,90(6):2920-2927
76.
Fish yield from catch data and from prediction models in Lake Kariba is compared to that in Lake Tanganyika. Fish yields from catch data in L. Tanganyika are above expectation from the rates of algal production, and this disparity is not experienced in L. Kariba. Of the two hypotheses that have been forwarded to explain the situation in L. Tanganyika — high trophic efficiency and high bacterial production, it is suggested that, with the experience from L. Kariba, only the hypothesis of high bacteria production could be important.This paper is published with the permission of the Director, National Parks and WildLife Management, Zimbabwe. 相似文献
77.
The objective of this study was to examine the effect of dietary n-3 polyunsaturated fatty acid (PUFA) supplementation of rams on semen quality and subsequent sperm function of liquid stored semen. Mature rams of proven fertility were individually housed and were blocked according to breed, body weight, and body condition score and randomly allocated within block to one of two dietary treatments (N = 7 per treatment). Rams were offered a base diet of hay and concentrate, with the concentrate enriched with either: (1) saturated palmitic acid (CON) or (2) high n-3 PUFA fish oil (FO) supplements. Both lipid supplements were added at 2% (wt/wt) of the total diet as fed and both were partially rumen-protected. The animals were fed their respective diets for a total of 9 weeks and blood samples were collected on weeks 0 (pre-experimental), 4, and 9, relative to initial allocation of diet (week 0), for measurement of plasma concentration of fatty acids, metabolites, insulin like growth factor 1 (IGF-1) and insulin. Semen was collected from each ram (on 1 day in each week) in weeks 4, 5, 7, 8, and 9, and each ejaculate was assessed for volume, wave motion, and concentration of sperm, after which it was diluted in a skim milk-based extender and stored at 4 °C. A second ejaculate was collected on weeks 4, 7, and 9, centrifuged, and the sperm frozen for subsequent lipid analysis. A sample of semen from each ram was assessed at 24, 48, and 72 hours after collection for sperm progressive linear motion, ability to penetrate artificial mucus, and the ability to resist lipid peroxidation (at 24 and 48 hours only) using the thiobarbituric acid reactive substances assay. There was no effect of diet on plasma insulin concentrations or on any of the metabolites measured, however, there was a diet by week interaction for plasma IGF-1 concentration (P < 0.05). This was manifested as the FO supplemented rams having higher IGF-1 concentrations on week 9 compared with the control treatment (P < 0.05), but not at the earlier sampling dates. Compared with the pre-experimental values, supplementation with FO increased plasma concentrations of total n-3 PUFAs by 3.1-fold and decreased n-6 PUFA concentrations by 1.84-fold. Consequently, the ratio of n-6 to n-3 PUFA was decreased in the FO-supplemented rams (P < 0.001). Dietary supplementation with FO increased the concentration of eicosapentaenoic acid in sperm from week 4 to 9 by 2.7-fold (P < 0.05) leading to a 1.5-fold increase in total n-3 PUFA in the same period. Ejaculates collected from rams supplemented with FO yielded a higher semen concentration (P < 0.05), however, there was no difference between diets on any of the other semen quality parameters including semen volume, wave motion, progressive linear motion, ability to penetrate artificial mucus, or ability to resist lipid peroxidation. In conclusion, dietary supplementation of rams with n-3 PUFA successfully increased the n-3 PUFA content of plasma and sperm but has limited effects on the quality of liquid stored semen. 相似文献
78.
79.
Duncan E. Govan William R. Fair Gerald W. Friedland Roy A. Filly 《The Western journal of medicine》1974,121(5):382-389
Of 134 girls with demonstrable ureterovesical reflux, 61 (105 ureters) had the reflux surgically corrected with an overall surgical cure rate of 97 percent. In the remaining 73 children (112 ureters), the reflux was treated conservatively with medical management alone. During the follow-up period no significant differences were demonstrated in the overall incidence of urinary tract infection; two years following corrective operation or medical treatment more than 50 percent of both medically and surgically treated children were still experiencing infections. A pronounced decrease, however, occurred in the incidence of clinical pyelonephritis among the surgically treated group. Following correction of reflux, the incidence of pyelonephritis was similar in both medically and surgically treated cases and was approximately the same as that found in a comparable group of children without reflux.In approximately two-thirds of refluxing renal units in which there was evidence of clubbing and scarring before medical or surgical therapy, deterioration progressed during the follow-up period. In most of these cases infection control was felt to be inadequate with episodes of clinical pyelonephritis occurring during the period of medical management, or, in the surgically treated group, occurring just before corrective operation and the scar appearing within two years after operation.The majority of renal units in which calyceal clubbing and parenchymal scarring was present had the most severe grades of reflux. 相似文献
80.
Ariel L. Rivas Mark D. Jankowski Renata Piccinini Gabriel Leitner Daniel Schwarz Kevin L. Anderson Jeanne M. Fair Almira L. Hoogesteijn Wilfried Wolter Marcelo Chaffer Shlomo Blum Tom Were Stephen N. Konah Prakash Kempaiah John M. Ong’echa Ulrike S. Diesterbeck Rachel Pilla Claus-Peter Czerny James B. Hittner James M. Hyman Douglas J. Perkins 《PloS one》2013,8(2)