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111.
A morphologically explicit numerical model for analysing wateruptake by individual roots was developed based on a conductornetwork, with specific conductors representing axial or radialconductivities for discrete root segments. Hydraulic conductivity(Lp; m s1 MPa1) was measured for roots of Agavedeserti Engelm. and Opuntia ficus-indica (L.) Miller by applyinga partial vacuum to the proximal ends of excised roots in solution.Lp was also measured for 40- to 80-mm segments along a root,followed by measurements of axial conductivity and calculationof radial conductivity. Predicted values of Lp for entire rootsbased on two to ten segments per root averaged 1.04±0.07(mean±s.e. mean for n = 3) of the measured Lp for A.deserti and 1.06±0.10 for O. ficus-indica. The modelalso closely predicted the drop in water potential along theroot xylem (xylem); when a tension of 50 kPa was applied tothe proximal ends of 0.2 m-long roots of A. deserti and O. ficus-indica,the measured xylem to midroot averaged 30 kPa compared witha predicted decrease of 36 kPa. Such steep gradients in xylemsuggest that the driving force for water movement from the soilto young distal roots may be relatively small. The model, whichagreed with an analytical solution for a simple hypotheticalsituation, can quantify situations without analytical solutions,such as when root and soil properties vary arbitrarily alonga root. Agave deserti, electrical circuit analog, hydraulic conductivity, Opuntia ficus-indica, water potential 相似文献
112.
Attached 2-month-old roots of the succulent plant, Opuntia ficus-indica,shrank 0.4% radially during periods of maximal transpirationunder wet conditions. In contrast, reversible decreases in diameterof nearly 20% occurred for these roots as their ambient waterpotential () in the vapour phase decreased from 0.01to 10 MPa over 8 d, the changes being slightly more rapidat 40 °C than at 10 °C. Such substantial diameter changesbecame progressively less with root age, from a 43% decreasein diameter at 3 weeks to a 6% decrease at 12 months Root shrinkagewas slight when was decreased from 0.01 to 0.3MPa, the latter being similar to the root water potential.As was further decreased from 0.3 to 10 MPa,water movement out of cortical cells caused considerable rootshrinkage. The root hydraulic conductivity (Lp) decreased only30 to 60% for a change in from 0.01 to 10 MPacompared with a decrease of over 106-fold for the soil hydraulicconductivity over this range. The overall conductivity of thesoil, the root-soil air gap, and the root was predicted to bedominated by Lp for soil above 0.3 MPa. As simulatedsoil decreased below 0.3 MPa, the root-soil air gap initiallybecame the primary limiter of water loss from the roots. Below5 MPa for 1-month-old roots and below 2 MPa for12-month-old roots, the soil became the main limiter of waterloss. Thus, water uptake from wet soils apparently was mainlycontrolled by root properties Water loss to drying soils wascontrolled by the development of a root-soil air gap aroundshrinking roots during the initial phase of soil drying andby the reduction of the soil hydraulic conductivity at evenlower soil. Root diameter, root hydraulic conductivity, root-soil air gap, soil hydraulic conductivity 相似文献
113.
Concentration of Cyclic Adenosine 3′,5′ -Monophosphate in Human Leucocytes during Phagocytosis 总被引:5,自引:0,他引:5
CYCLIC adenosine 3′,5′-monophosphate (cyclic AMP) has been established as a mediator of various hormonal effects in the appropriate target cells1. Adenyl cyclase converts adenosine triphosphate (ATP) to cyclic AMP and is widely distributed in the membrane of mammalian nucleated cells2–4. Since the early process of phagocytosis involves the physical and chemical contact of the cell membrane to the objects and subsequent formation of phagosome, we postulated that one of the earliest biochemical changes during phagocytosis might be an activation of adenyl cyclase and an alteration of concentrations of cyclic AMP in the phagocytes. 相似文献
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GYUNGAH KIM YOON MI JIN YEONSIL YU HA YEONG KIM SANGMEE AHN JO YOON JEONG PARK YOON SHIN PARK INHO JO 《Cytotherapy》2018,20(8):1013-1027
Background and aims
Osteoporosis, which is a disease characterized by weakening of the bone, affects a large portion of the senior population. The current therapeutic options for osteoporosis have side effects, and there is no effective treatment for severe osteoporosis. Thus, we urgently need new treatment strategies, such as topical therapies and/or safe and effective stem cell therapies.Methods
We investigated the therapeutic potential of directly injecting human tonsil-derived mesenchymal stem cells (TMSC) into the right proximal tibias of ovariectomized postmenopausal osteoporosis model mice. Injections were given once (1×) or twice (2×) during the 3-month experimental period. At the end of the experiment, micro-computed tomographic images revealed some improvement in the proximal tibias and more significant improvement in the femoral heads of treated mice.Results
Osteogenic effect was qualitatively and quantitatively more pronounced in TMSC/2×-treated mice. Furthermore, TMSC/2×?mice exhibited significant recovery of the serum osteocalcin level, which is pathologically elevated in osteoporosis, and increased serum alkaline phosphatase, which indicates bone formation. TMSC therapy was generally well tolerated and caused no apparent toxicity in the experimental mice. Moreover, TMSC therapy reduced visceral fat.Conclusion
Our results demonstrate that double injection of TMSC directly into the proximal tibia triggers recovery of osteoporosis, and thus could be a potential therapeutic approach for severe bone loss. 相似文献116.
GÉRALDINE LOOT YOUNG-SEUK PARK SOVAN LEK SÉBASTIEN BROSSE 《Biological journal of the Linnean Society. Linnean Society of London》2006,89(1):99-106
The present study aimed to understand how a parasite with a complex life cycle selects a given host succession when several potential hosts are present. Ligula intestinalis (Cestoda, Pseudophyllidea) was considered, which presents a life cycle with three hosts: copepod, fish, and piscivorous bird. Encounter probability between each pair of hosts was calculated for Lavernose-Lacasse gravel pit (France) using a sum of the product of the host abundances over time. Among four potential copepod hosts, two potential fish hosts, and six potential bird hosts, the results demonstrate that the copepod Eudiaptomus gracilis , the roach ( Rutilus rutilus ), and the great crested grebe ( Podiceps cristatus ) had a maximal encounter probability due to their abundance, but also due to the similarities of the temporal dynamics of their life cycles. These results agree with previous experiments and field work identifying a high specificity of L. intestinalis to E. gracilis , R. rutilus , and P. cristatus in the study site. This suggests that the abundance of potential hosts and the temporal dynamics of their life cycles act together to determine encounter rates between hosts and parasites, and thus could constitute a crucial determinant in local host selection by parasites with a complex life cycle. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 99–106. 相似文献
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119.
Water Influx Characteristics and Hydraulic Conductivity for Roots of Agave deserti Engelm. 总被引:4,自引:0,他引:4
NOBEL PARK S.; SCHULTE PAUL J.; NORTH GRETCHEN B. 《Journal of experimental botany》1990,41(4):409-415
Various plant and environmental factors influence the hydraulicproperties for roots, which were examined using negative hydrostaticpressures applied to the proximal ends of individual excisedroots of a common succulent perennial from the Sonoran Desert,Agave deserti Engelm. The root hydraulic conductivity, Lp, increasedsubstantially with temperature, the approximately 4-fold increasefrom 0.5°C to 40°C representing a Q10 of 1.45. Suchvariations in Lp with temperature must be taken into accountwhen modelling water uptake, as soil temperatures in the rootzone of such a shallow-rooted species vary substantially bothdaily and seasonally. At 20°C, Lp was 2.3 x 107 ms{macron}1MPa{macron}1for 3-week-old roots, decreasing to abouthalf this value at 10 weeks and then becoming approximatelyhalved again at 6 months. For a given root age, Lp for rainroots that are induced by watering as lateral branches on theestablished roots (which arise from the stem base) was aboutthe same as Lp for established roots. Hence, the conventionalbelief that rain roots have a higher Lp than do establishedroots is more a reflection of root age, as the rain roots tendto be shed following drought and thus on average are much youngerthan are established roots. Unlike previous measurements onroot respiration, lowering the gas-phase oxygen concentrationfrom 21% to 0% or raising the carbon dioxide concentration from0.1% to 2% had no detectable effect on Lp for rain roots andestablished roots. Lp for rain roots and established roots wasdecreased by an average of 11% and 35% by lowering the soilwater potential from wet conditions (soil=0 kPa) to {macron}40kPa and {macron}80 kPa, respectively. Such decreases in Lp mayreflect reduced water contact between soil particles and theroot surface and should be taken into account when predictingwater uptake by A. deserti. Key words: Gas phase, rain roots, root age, soil, temperature, water potential 相似文献
120.
Influences of Water Status, Temperature, and Root Age on Daily Patterns of Root Respiration for Two Cactus Species 总被引:4,自引:1,他引:3
Daily patterns of root respiration measured as CO2, efflux werestudied at various soil water potentials, temperatures, androot ages for individual, attached roots of the barrel cactusFerocactus acanthodes and the platyopuntia Opuntia ficus-indica.The daily patterns of root respiration for both establishedroots and rain roots followed the daily patterns of root temperature.Root respiration increased when root temperature was raisedfrom 5 °C to 50 °C for F. acanthodes and from 5 °Cto 55 °C for O. ficus-indica; at 60 °C root respirationdecreased 50° from the maximum for F. acanthodes and decreased25° for O. ficus-indica. Root respiration per unit d. wtdecreased with root age for both species, especially for rainroots. Root respiration rates for rain roots were reduced tozero at a soil water potential ( 相似文献