Preferential flow descriptions for structured soils   总被引：3，自引：0，他引：3  

Horst H. Gerke 《植物养料与土壤学杂志》2006,169(3):382-400

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Role of root-induced changes in the rhizosphere for iron acquisition in higher plants     

Horst Marschner  Michael Treeby  Volker Rmheld 《植物养料与土壤学杂志》1989,152(2):197-204

Plants can mobilize iron (Fe) in the rhizosphere by non-specific and specific (adaptive) mechanisms. Non-specific mechanisms are, for example, rhizosphere acidification related to high cation-anion uptake ratios, or citric acid excretion. The specific mechanisms are root responses to Fe deficiency and can be classified into two different strategies. The Strategy I is typical for dicots and monocots except for grasses (graminaceous species) and is characterized by increased plasma membrane-bound reductase activity, enhanced net excretion of protons and enhanced release of reducing compounds, mainly phenolics. The reductase activity is stimulated by low pH, and with supply of Fe^III chelates, ferric reduction at the plasma membrane takes place prior to uptake. In contrast, in graminaceous species (Strategy II) these root responses are absent, but enhancement of release of Fe^III chelating compounds - phytosiderophores - takes place. These phytosiderophores are very efficient in mobilizing Fe^III from artificially prepared sparingly soluble inorganic compounds (e.g. Fe^III hydroxide) and from calcareous soils. The ferrated phytosiderophores are taken up by grasses at rates 10² to 10³ times higher than Fe supplied either as synthetic chelate or microbial siderophores (e.g. ferrioxamine B), indicating a specific membrane transport system for ferrated phytosiderophores in roots of grasses. In calcareous soils phytosiderophores not only mobilize Fe, but also Zn, Mn, and Cu by chelation. However, only the Fe^III phytosiderophores are taken up preferentially by Fe deficient grasses. The ecological advantages and disadvantages of Strategy I and Strategy II for Fe acquisition from calcareous soils are discussed.  相似文献   

Symptome von Mangan-Überschuß bei Bohnen (Phaseolus vulgaris)     

W. J. Horst  H. Marschner 《植物养料与土壤学杂志》1978,141(2):129-142

Symptoms of manganese toxicity in beans (Phaseolus vulgaris L) In water culture experiments with bush bean plants (Phaseolus vulgaris L. var. ?Red Kidney”?) the macro- and micro-symptoms of manganese toxicity had been studied. Typical symptoms of Mn toxicity are small distinct blackish-brown spots, first at the older leaves and at more severe toxicity also at the petals and stems. Using the autoradiographic technique on ⁵⁴Mn-distribution and comparing this with corresponding light microscopic studies it could be demonstrated that the blackish-brown spots in the leaves resemble Mn-precipitations. These precipitations are Mn-compounds of higher oxidated form and are primarily localized in the walls of cells in vicinity of the vessels. The extend to which these precipitations occur is not only a function of the Mn-content of the leaves but also of their age. At comparable Mn-content the extend of the precipitation increases with the leaf age. As secondary symptom of Mn-toxicity under certain conditions (presence of silicon e.g.) induced Fe deficiency (chlorosis of the youngest leaves) and Ca deficiency (?crinkle leaf”?) may occur. It is assumed that the process of Mn precipitation within the leaves is enzymatically regulated. The severe reduction in the growth of leaf blades at Mn toxicity is presumably related to an interference with the growth hormon balance.  相似文献   

A possible relativistic jetted outburst from a massive black hole fed by a tidally disrupted star     

Bloom JS  Giannios D  Metzger BD  Cenko SB  Perley DA  Butler NR  Tanvir NR  Levan AJ  O'Brien PT  Strubbe LE  De Colle F  Ramirez-Ruiz E  Lee WH  Nayakshin S  Quataert E  King AR  Cucchiara A  Guillochon J  Bower GC  Fruchter AS  Morgan AN  van der Horst AJ 《Science (New York, N.Y.)》2011,333(6039):203-206

Gas accretion onto some massive black holes (MBHs) at the centers of galaxies actively powers luminous emission, but most MBHs are considered dormant. Occasionally, a star passing too near an MBH is torn apart by gravitational forces, leading to a bright tidal disruption flare (TDF). Although the high-energy transient Sw 1644+57 initially displayed none of the theoretically anticipated (nor previously observed) TDF characteristics, we show that observations suggest a sudden accretion event onto a central MBH of mass about 10(6) to 10(7) solar masses. There is evidence for a mildly relativistic outflow, jet collimation, and a spectrum characterized by synchrotron and inverse Compton processes; this leads to a natural analogy of Sw 1644+57 to a temporary smaller-scale blazar.  相似文献   

Documenting Lysenkoism     

Malke H 《Science (New York, N.Y.)》2002,297(5587):1646-7; author reply 1646-7

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Influence of cultivar and cutting date on the fatty acid composition of perennial ryegrass (Lolium perenne L.)     

A. Elgersma  G. Ellen†  H. Horst Van der‡  B. G. Muuse†  H. Boer‡  S. Tamminga‡ 《Grass and Forage Science》2004,59(1):104-105

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Influence of Various Factors on Circulating 25(OH) Vitamin D Concentrations in Dogs with Cancer and Healthy Dogs          下载免费PDF全文

N. Weidner  J.P. Woods  P. Conlon  K.A. Meckling  J.L. Atkinson  J. Bayle  A.J. Makowski  R.L. Horst  A. Verbrugghe 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2017,31(6):1796-1803

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The use of vitamin D3 to improve beef tenderness   总被引：7，自引：0，他引：7  

Montgomery JL  Parrish FC  Beitz DC  Horst RL  Huff-Lonergan EJ  Trenkle AH 《Journal of animal science》2000,78(10):2615-2621

An experiment was designed to test the hypothesis that short-term oral administration of dietary vitamin D3 to beef cattle before slaughter would increase beef tenderness through greater calcium-activated calpain activity in postmortem aged skeletal muscle. Thirty continental crossbred steers were allotted randomly to three treatment groups housed in one pen. One group served as a control; two other groups were administered boluses with either 5 x 10(6) or 7.5 x 10(6) IU of vitamin D3 daily for 9 d. Cattle were slaughtered 1 d later. The longissimus lumborum was excised from each carcass 72 h postmortem and steaks removed at 3, 7, 14, and 21 d postmortem. The semimembranosus muscle (top round) was excised from each carcass 72 h postmortem and steaks removed at 7, 14, and 21 d postmortem. Blood plasma calcium concentration of cattle treated with 5 or 7.5 x 10(6) IU of vitamin D3 was higher (P < .05) than that of controls. Strip loin and top loin steaks from cattle fed supplemental doses of vitamin D3 had lower (P < .05) Warner-Bratzler (W-B) shear values at 14 d postmortem but were not significantly different from controls at 3, 7, or 21 d (strip loins) or 7 or 21 d (top rounds). No significant difference in strip loin steak tenderness was observed by sensory panel at 14 d postmortem (P < .17) between steaks from control and vitamin D3-treated steers. At 14 d postmortem, strip loin and top round steaks from cattle fed 5 x 10(6) IU of vitamin D3, but not from those given 7.5 x 10(6) IU, showed more proteolysis (P < .05) than did steaks from control cattle, based on Western blotting analysis. Therefore, the use of supplemental dietary vitamin D3 given daily for 9 d before slaughter did improve tenderness (lower W-B shear values) of 14-d postmortem aged beef. Increased proteolysis seems to be the mechanism of tenderization.  相似文献