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排序方式: 共有893条查询结果,搜索用时 9 毫秒
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Chiara Pavanello Alice Ossoli Arianna Strazzella Patrizia Risè Fabrizio Veglia Marie Lhomme Paolo Parini Laura Calabresi 《Journal of lipid research》2022,63(7):100232
Mutations in the LCAT gene cause familial LCAT deficiency (Online Mendelian Inheritance in Man ID: #245900), a very rare metabolic disorder. LCAT is the only enzyme able to esterify cholesterol in plasma, whereas sterol O-acyltransferases 1 and 2 are the enzymes esterifying cellular cholesterol in cells. Despite the complete lack of LCAT activity, patients with familial LCAT deficiency exhibit circulating cholesteryl esters (CEs) in apoB-containing lipoproteins. To analyze the origin of these CEs, we investigated 24 carriers of LCAT deficiency in this observational study. We found that CE plasma levels were significantly reduced and highly variable among carriers of two mutant LCAT alleles (22.5 [4.0–37.8] mg/dl) and slightly reduced in heterozygotes (218 [153–234] mg/dl). FA distribution in CE (CEFA) was evaluated in whole plasma and VLDL in a subgroup of the enrolled subjects. We found enrichment of C16:0, C18:0, and C18:1 species and a depletion in C18:2 and C20:4 species in the plasma of carriers of two mutant LCAT alleles. No changes were observed in heterozygotes. Furthermore, plasma triglyceride-FA distribution was remarkably similar between carriers of LCAT deficiency and controls. CEFA distribution in VLDL essentially recapitulated that of plasma, being mainly enriched in C16:0 and C18:1, while depleted in C18:2 and C20:4. Finally, after fat loading, chylomicrons of carriers of two mutant LCAT alleles showed CEs containing mainly saturated FAs. This study of CEFA composition in a large cohort of carriers of LCAT deficiency shows that in the absence of LCAT-derived CEs, CEs present in apoB-containing lipoproteins are derived from hepatic and intestinal sterol O-acyltransferase 2. 相似文献
4.
T. E. HUMPHREYS 《Plant, cell & environment》1987,10(3):259-266
Abstract During incubation of maize scutellum slices in fructose, there was an efflux of sucrose. Efflux was constant for at least 4 h at fructose concentrations of 70 or 100 mol m?3. Efflux was increased by EDTA, and decreased by Ca2+. Efflux was independent of pH after EDTA treatment, but increased from untreated slices when the pH was lowered from 7 to 4. Uranyl ion and PCMBS (p-chloro-mercuribenzenesulfonic acid) abolished sucrose uptake, but were only weak inhibitors of sucrose efflux. These results are consistent with efflux occurring by simple diffusion through aqueous pores, but they do not rule out facilitated diffusion. Rates of sucrose export from the scutellum to the root shoot axis were estimated from measurements of axis respiration and dry weight gain. Sucrose efflux from scutellum slices was only 14-22% of the export rate. Sucrose efflux from the whole scutellum was only 3-4% of the export rate. It is concluded that the observed efflux is from leaky cells and does not represent sucrose on the way to the phloem along a path that includes the apoplast. These results support the idea that the path for sucrose from parenchyma cell to sieve tube in the maize scutellum is entirely symplastic. 相似文献
5.
Careful cutting of the hypocotyl of Ricinus communis L. seedlings led to the exudation of pure sieve-tube sap for 2–3 h. This offered the possibility of testing the phloem-loading system qualitatively and quantitatively by incubating the cotyledons with different solutes of various concentrations to determine whether or not these solutes were loaded into the sieve tubes. The concentration which was achieved by loading and the time course could also be documented. This study concentrated on the loading of sucrose because it is the major naturally translocated sieve-tube compound. The sucrose concentration of sieve-tube sap was approx. 300 mM when the cotyledons were buried in the endosperm. When the cotyledons were excised from the endosperm and incubated in buffer, the sucrose concentration decreased gradually to 80–100 mM. This sucrose level was maintained for several hours by starch breakdown. Incubation of the excised cotyledons in sucrose caused the sucrose concentration in the sieve tubes to rise from 80 to 400 mM, depending on the sucrose concentration in the medium. Thus the sucrose concentration in the sieve tubes could be manipulated over a wide range. The transfer of labelled sucrose to the sieve-tube sap took 10 min; full isotope equilibration was finally reached after 2 h. An increase of K+ in the medium or in the sieve tubes did not change the sucrose concentration in the sievetube sap. Similarly the experimentally induced change of sucrose concentration in the sieve tubes did not affect the K+ concentration in the exudate. High concentrations of K+, however, strongly reduced the flow rate of exudation. Similar results were obtained with Na+ (data not shown). The minimum translocation speed in the sieve tubes in vivo was calculated from the growth increment of the seedling to be 1.03 m·h-1, a value, which on average was also obtained for the exudation system with the endosperm attached. This comparison of the in-vivo rate of phloem transport and the exudation rate from cut hypocotyls indicates that sink control of phloem transport in the seedlings of that particular age was small, if there was any at all, and that the results from the experimental exudation system were probably not falsified by removal of the sink tissues.Abbreviations PTS
3-hydroxy-5,8, 10-pyrenetrisulfonate 相似文献
6.
Current perspectives on plasmodesmata: structure and function 总被引:2,自引:0,他引:2
Recent studies on plasmodesmata have shown that these important intercellular passages for communication and transport are much more sophisticated in both structure and regulatory abilities than previously imagined. A complex, but not well understood, substructure has been revealed by a variety of increasingly reliable ultrastructural techniques. Proteinaceous particles are seen within the cytoplasmic sleeve surrounding the desmotubule. Dye-coupling studies have provided experimental evidence for the physical pathway of solute movement, supporting conclusions about substructural dimensions within plasmodesmata drawn from the ultrastructural studies. Calcium has been identified as a major factor in the regulation of intercellular communication via plasmodesmata. Evidence from studies on virus movement through plasmodesmata suggests a direct interaction between virallycoded movement proteins and plasmodesmata in the systemic spread of many viruses. There is increasing evidence, albeit indirect, that in some plant species phloem loading may involve transport of photoassimilate entirely within the symplast from mesophyll cells to the sieve element-companion cell complexes of minor veins. 相似文献
7.
Hans Sding 《Plant biology (Stuttgart, Germany)》1985,98(1):209-226
1. Die anscheinend in Vergessenheit geratenen älteren Angaben von HÄRDTL (1927 und spärer) und PRINGSHEIM (1931), nach denen einseitig belastete Blätter Gleichgewichtsbewegungen ausführen können (Isoklinotropismus nach HÄRDTL), wurden an mehreren Arten (Chelidonium majus, Aegopodium podagra ria, Ranunculus repens, Sambucus nigra, Coleus blumei und Hibiscus rosa sinensis) bestätigt,— Die einseitige Belastung erfolgte durch Einstecken von Nadeln in die eine Hälfte der Blattspreite bzw. in eine Blattfieder. 2. Bei Blättern, die in Spreite oder Stiel epinastisch gekrtimmt sind (die überwiegende Mehrzahl) oder auch durch die Belastung abwärts gebogen sind, kommt es dabei zu zwei verschiedenen Reaktionen: a) zu einer sofort eintretenden rein physikalischen reversiblen Reaktion, da die einseitige Last eine Torsion der Spreite bewirkt, die die Spreitenspitze nach der der Last gegenüberliegenden Seite [führt, und b) zu einer spärer eintretenden physiologischen Reaktion durch eine Wachstumskrümmung nach derselben Seite, - Beide Komponenten der Bewegung ftihren zu einer Verringerung oder einem Ausgleich des Ungleichgewichtes. 3. Die physiologische Reaktion war meist nach einem oder einigen Tagen erkennbar, bei Chelidonium mitunter schon nach einigen Stunden, bei Hibiscus gelegentlich erst nach etwa einer Woche. Mitunter blieb die Reaktion auch aus. Bei den gefiederten Blattern erfolgte sie in der Rhachis, ober- und unterhalb der belasteten Fieder, mitunter auch im Blattstiel, bei Coleus im Spreitengrund und im Blattstiel, bei Hibiscus im oberen Gelenkpolster (“Sekundargelenk”) des Blattstiels. Auch ältere Blätter reagierten oft noch überraschend gut. Vielfach führte die physiologische Reaktion zu einer vollständigen Ausbalancierung der einseitig belasteten Blattspreite. Auf nachtragliche Entfernung der eingesteckten Nadeln gingen auch die Krtimmungen in 2–3 Tagen wieder weitgehend zurück. 4. Als Ursache ftir die Gleichgewichtsbewegungen der Blätter kommen zwei verschiedene Mechanismen in Betracht: a) Infolge der durch die einseitige Belastung hervorgerufenen Schräglage der Blattspreite sammelt sich das Auxin auf der tiefer liegenden Flanke von Mittelnerv bzw. Rhachis und Blattstiel an, was zu einem stärkeren Wachstum dieser Seite und einer Gleichgewichtskrümmung führen muß. Nach dieser Auffassung ordnet sich der Isoklinotropismus dem Gravitropismus ein. b) Die nach der Belastung sofort eintretende auf der Torsionsspannung beruhende rein physikalische und zunächst reversible Gleichgewichtsreaktion des Blattes wird nach einigen Stunden oder Tagen teilweise irreversibel. (Für die spannungsfreien Abschnitte der Rhachis eines gefiederten Blattes oberhalb der Belastung kann diese Erklärung natürlich nicht gelten). Vermutlich sind beide Mechanismen, vor allern wohl der erstgenannte, bei den einzelnen Arten in verschiedenem Maße, als Ursache der Gleichgewichtsbewegungen wirksam. 5. Der biologische Sinn der Ausbalancierung eines (größeren) Blattes (PRINGSHELM 1931, HÄRDTL 1927, 1937 a) liegt darin, daß a) ein ausbalanciertes Blatt den geringsten Aufwand an mechanischen Elementen erfordert, und b) Photo- und Gravitropismus nur ein ausbalanciertes Blatt ohne Komplikationen in die angestrebte Lage fuhren konnen. 相似文献
8.
The loading of amino acids and nitrate into the xylem was investigated by collection and analysis of root-pressure exudate from the cut hypocotyl stumps of seedlings of Ricinus communis L. Glutamine was found to be the dominant amino acid in the exudate and also to be the amino acid which is transferred to the xylem most rapidly and accumulated to the greatest extent. The comparison between uptake and xylem loading showed significant differences in specificity between these two transport reactions, indicating a different set of transport systems. Nitrate is transferred to the xylem at a higher relative rate than any amino acid despite the great nitrate-storage capacity of the root system. Thus the supply of nitrate to Ricinus plants leads to enhanced nitrogen allocation to the shoots. 相似文献
9.
Barley leaf protoplasts were incubated in light or darkness in the presence of various inhibitors, metabolites or weak acids/bases. Nitrate reductase (NR) and phosphoenolpyruvate carboxylase (PEPCase) were rapidly extracted from the protoplasts and assayed under sub-optimal conditions, i.e. in the presence of Mg2+ and malate, respectively. Under these conditions changes in activities are thought to reflect changes in the phosphorylation states of the enzymes. The NR was activated by illumination to 90% of its maximal activity within 10 min. Photosynthetic electron transport appeared necessary for light activation of NR since activation was inhibited by the photosynthetic electron-transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and, additionally, an electron acceptor (HCO
3
-
) was required. The PEPCase was also activated by light. However, this activation was not prevented by DCMU or lack of HCO
3
-
. Loading of protoplasts in the dark with a weak acid resulted in activation of both NR and PEPCase. For NR, full activation was completed within 5 min, whereas for PEPCase a slower, modest activation continued for at least 40 min. Incubation of protoplasts with a weak base also gave activation of PEPCase, but not of NR. On the contrary, base loading counteracted light activation of NR. Since several treatments tested resulted in the modulation of either NR or PEPCase activity, but not both, signal transduction cascades leading to changes in activities appear to be very different for the two enzymes.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron)
- DMO
5,5-dimethyl-2,4 oxazolidinedione
- NR
nitrate reductase
- PEPCase
Phosphoenolpyruvate carboxylase
This work was supported by the Norwegian Research Council by a Grant to C.L: L.H.S. was supported by the Biotechnology and Biological Sciences Research Council. 相似文献
10.
Large, intermediate, and small bundles and contiguous tissues of the leaf blade of Hordeum tvulgare L. ‘Morex’ were examined with the transmission electron microscope to determine their cellular composition and the distribution and frequency of the plasmodesmata between the various cell combinations. Plasmodesmata are abundant at the mesophyll/parenchymatous bundle sheath, parenchymatous bundle sheath/mestome sheath, and mestome sheath/vascular parenchyma cell interfaces. Within the bundles, plasmodesmata are also abundant between vascular parenchyma cells, which occupy most of the interface between the sieve tube-companion cell complexes and the mestome sheath. Other vascular parenchyma cells commonly separate the thick-walled sieve tubes from the sieve tube-companion cell complexes. Plasmodesmatal frequencies between all remaining cell combinations of the vascular tissues are very low, even between the thin-walled sieve tubes and their associated companion cells. Both the sieve tube-companion cell complexes and the thick-walled sieve tubes, which lack companion cells, are virtually isolated symplastically from the rest of the leaf. Data on plamodesmatal frequency between protophloem sieve tubes and other cell types in intermediate and large bundles indicate that they (and their associated companion cells, when present) are also isolated symplastically from the rest of the leaf. Collectively, these data indicate that both phloem loading and unloading in the barley leaf involve apoplastic mechanisms. 相似文献