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941.
Renal hemodynamic responses to dynamic exercise in rabbits 总被引:2,自引:0,他引:2
Mueller Patrick J.; O'Hagan Kathleen P.; Skogg Kara A.; Buckwalter John B.; Clifford Philip S. 《Journal of applied physiology》1998,85(5):1605-1614
Cardiovascular hemodynamics, including renalblood flow, were measured in rabbits with one intact and one denervatedkidney during various intensities of treadmill exercise. Within thefirst 10 s of exercise, there was rapid vasoconstriction in theinnervated kidney associated with decreases in renal blood flow (range10 to 17%). The vasoconstriction in the innervatedkidney was evident at all workloads and was intensity dependent. Therewas no significant vasoconstriction or change in renal blood flow(range 0.5 to 3.1%) in the denervated kidney at the onset ofexercise. However, a slowly developing vasoconstriction occurred in thedenervated kidney as exercise progressed to 2 min at all workloads.Examination of responses to exercise performed under -adrenergicblockade with phentolamine (5 mg/kg iv) revealed that thevasoconstriction in the innervated kidney at the onset of exercise andthe delayed vasoconstriction in the denervated kidney were dueprimarily to activation of -adrenergic receptors. Inaddition, a residual vasoconstriction was also present in theinnervated kidney after -adrenergic blockade, suggesting that,during exercise, activation of other renal vasoconstrictor mechanismsoccurs which is dependent on the presence of renal nerves. 相似文献
942.
Britta Herzog Susanne Hoffmann W. Hartung U. Lüttge 《Plant biology (Stuttgart, Germany)》1999,1(4):460-470
Abstract: Clusia multiflora H. B. K., an obligate C3 species and Clusia minor L. a C3/CAM intermediate species, are two physio-types of a similar morphotype. They can sympatrically occupy secondary savanna sites exposed to high insolation in the tropics. In C. multiflora severe stress, i.e., switching shade-grown plants to high light plus drought, resulted in leaves browning or yellowing and becoming necrotic. However, in long-term light stress C. multiflora was able to grow new leaves with their photosynthetic apparatus fit for high light conditions. Shade-grown C. minor readily overcame switching to high light conditions and drought, responding by a rapid change from C3 photosynthesis to CAM. Decreasing soil led to increased abscisic acid levels in the leaves of C. minor, however CAM induction was not directly related to this and was mainly determined by increased PPFD. Both species were capable of rapid accumulation of zea-xanthin for acute photoprotection following high PPFD exposure. The maximum capacity for zeaxanthin accumulation was larger in C. minor, but under steady high PPFD it only partially made use of this capacity, relying on high internal CO2 concentrations of Phase Ill of CAM, in addition to zeaxanthin, for acute photo-protection. Thus, by different means the two species perform well under high light conditions. However, C. multiflora needs time for development of adapted leaves under such stress conditions while the more flexible C. minor can readily switch from low light to high light conditions. 相似文献
943.
Gervais Frank; Siedel Ulrike; Heilmann Britta; Weithoff Guntram; Heisig-Gunkel Gabriele; Nicklisch Andreas 《Journal of plankton research》2003,25(3):273-278
A characteristic vertical sequence of phytoplankton populationswas observed below the metalimnetic oxycline of a stratified,mesotrophic lake. Ceratium spp., Closterium acutum and Aphanizomenonflos- aquae were present in the epilimnion but had distinctpopulation maxima in the microaerobic chemocline. Below thesepopulations, Cryptomonas phaseolus, Planktothrix clathrata,Pseudanabaena catenata and Limnothrix sp. followed each otherin the transition zone between the chemocline and the sulphide-containinghypolimnion. The dominating populations of P. clathrata andP. catenata caused a deep chlorophyll maximum. Phytoplanktonstructure was determined by the vertical gradients of sulphideand light. Compared with the epilimnion, nutrient availabilitywas not fundamentally better below the oxycline but the algaemight have benefited from reduced grazing pressure in theirhabitat. 相似文献
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Specific leaf weight, percent moisture, and free sugar, starch, and amino nitrogen content of soybean (Glycine max (L.) Merrill) leaves were measured at 1, 3, 7, and 10 day(s) after petiole girdling by threecornered alfalfa hopper,Spissistilus festinus (Say) (Homoptera: Membracidae) nymphs. Leaf starch was increased at 1, 3, and 7 day(s) after girdling and largely accounted
for corresponding increases in specific leaf weight and decreases in percent moisture, free sugars, and amino nitrogen. Specific
leaf weight was increased at 10 days after girdling despite no increase in starch. Amino nitrogen content was decreased 10
days after girdling. When leaf dry weights were corrected for starch, free sugar content was not affected by girdling, and
amino nitrogen content was reduced only at 3 and 10 days. The amino nitrogen: free sugar ratio was reduced only at 10 days
after girdling. Changes in leaf starch indicated a rapid but reversible effect of girdling on leaf carbohydrate metabolism. 相似文献
947.
Sanna R. Piilo Minna M. Väliranta Matt J. Amesbury Marco A. Aquino-López Dan J. Charman Angela Gallego-Sala Michelle Garneau Natalia Koroleva Mai Kärppä Anna M. Laine A. Britta K. Sannel Eeva-Stiina Tuittila Hui Zhang 《Global Change Biology》2023,29(6):1530-1544
Climate warming is leading to permafrost thaw in northern peatlands, and current predictions suggest that thawing will drive greater surface wetness and an increase in methane emissions. Hydrology largely drives peatland vegetation composition, which is a key element in peatland functioning and thus in carbon dynamics. These processes are expected to change. Peatland carbon accumulation is determined by the balance between plant production and peat decomposition. But both processes are expected to accelerate in northern peatlands due to warming, leading to uncertainty in future peatland carbon budgets. Here, we compile a dataset of vegetation changes and apparent carbon accumulation data reconstructed from 33 peat cores collected from 16 sub-arctic peatlands in Fennoscandia and European Russia. The data cover the past two millennia that has undergone prominent changes in climate and a notable increase in annual temperatures toward present times. We show a pattern where European sub-Arctic peatland microhabitats have undergone a habitat change where currently drier habitats dominated by Sphagnum mosses replaced wetter sedge-dominated vegetation and these new habitats have remained relatively stable over the recent decades. Our results suggest an alternative future pathway where sub-arctic peatlands may at least partly sustain dry vegetation and enhance the carbon sink capacity of northern peatlands. 相似文献
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