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1.
Of nine organotin compounds tested towards the marine yeastDebaryomyces hansenii, only triphenyltin chloride (Ph3SnCl) and mono-, di-, and tributyltin chloride induced significant K+ release from cells which was symptomatic of viability loss. The general order of toxicity of the butylated compounds was tributyltin chloride (Bu3SnCl) > monobutyltin chloride (BuSnCl3) dibutyltin chloride (Bu2SnCl2). The overall toxicity of Ph3SnCl was similar to BuSnCl3. Release of K+ induced by butylated tin compounds or by Ph3SnCl was strongly dependent on the external pH. Maximal toxicity occurred at pH 6.5 for Bu3SnCl, BuSnCl3, and Ph3SnCl, whereas maximal toxicity of Bu2SnCl2 occurred at pH 5.0. Toxicity was decreased above or below these values. The toxicity of BuSnCl3, Bu3SnCl, and Ph3SnCl was reduced at salinity levels approximating to sea water conditions. Prior growth ofD. hansenii in 3% (w/v) NaCl also resulted in reduced sensitivity to Bu3SnCl as evidenced by a decreased rate and extent of K+ efflux. Bu3SnCl-induced Na+ release from cells grown in the absence or presence of 3% (w/v) NaCl was low and similar in both cases. It appeared that the monovalent cation was important in the reduction of Bu3SnCl toxicity since Na2SO4 had a similar protective effect as NaCl while CsCl completely prevented K+ efflux. Thus, the effects of external NaCl were related both to Na+ and to Cl–. These results emphasize that cellular and environmental factors influence the toxic effects of organotins and suggests that these compounds may be more effective antimicrobial agents in some environmental niches than in others. 相似文献
2.
Summary
Debaryomyces hansenii (NCYC 459 and strain 75-21),Candida albicans (3153A),Saccharomyces cerevisiae (X2180-1B),Rhodotorula rubra (NCYC 797) andAureobasidium pullulans (IMI 45533 and ATCC 42371) were grown on solid medium supplemented with varying concentrations of AgNO3. Although Ag+ is highly toxic towards yeasts, growth on solid media was still possible at Ag concentrations of 1–2 mM. Further subculture on higher Ag concentrations (up to 5 mM) resulted in elevated tolerance. The extent of Ag tolerance depended on whether Ag-containing plates were exposed to light prior to inoculation since light-mediated reduction of Ag+ to Ag0 resulted in the production of a less toxic silver species. Experimental organisms exhibited blackening of colonies and the surrounding agar during growth on AgNO3-containing medium especially at the highest Ag concentrations tested. All organisms accumulated Ag from the medium; electron microscopy revealed that silver was deposited as electron-dense granules in and around cell walls and in the external medium. X-ray microprobe analysis indicated that these granules were metallic Ag0 although AgCl was also present in some organisms. Volatile and non-volatile reducing compounds were produced by several test organisms which presumably effected Ag+ reduction to Ag0. 相似文献
3.
Interactions among Ca2+, Na+ and K+ in salinity toxicity: quantitative resolution of multiple toxic and ameliorative effects 总被引:5,自引:0,他引:5
Root elongation by wheat seedlings (Triticum aestivum
L. cv. Scout 66) was not inhibited by NaCl or KCl up to 130 mM in culture
solutions or by high Na+ (2 mg
g-1 FW) or K+ (4 mg
g-1 FW) in the root tissue, provided that
[Ca2+]>2 mM in the rooting medium. At [NaCl],
[KCl], or [mannitol] >250 mOs, root elongation was progressively
inhibited, irrespective of high [Ca2+]. In contrast,
shoot elongation was sensitive to any diminution of water potential, and
Ca2+ alleviated the toxicity only weakly. At solute
concentrations <250 mOs, the following interactions were observed.
Ca2+ alleviated Na+ and
K+ toxicity to roots by at least three separate
mechanisms. K+ was more toxic to roots than
Na+, but Na+ was more toxic
to shoots. Low levels of K+ relieved
Na+ toxicity, but low levels of
Na+ enhanced K+ toxicity.
Tissue concentrations of Na+ were reduced by
Ca2+ and K+ in the rooting
medium, and tissue concentrations of K+ were
enhanced by Ca2+ and Na+.
Several hypotheses relating to salinity toxicity can be evaluated, at least
for wheat seedlings. The osmoticant hypotheses (salinity intoxication
occurs because of diminished water potential) is true for shoots at all
salinity levels, but is true for roots only at high salinity. The
Ca2+-displacement hypothesis
(Na+ is toxic because it displaced
Ca2+ from the cell surface) is correct, but often of
minor importance. The K+-depletion hypothesis
(Na+ is toxic because it causes a loss of
K+ from plant tissues) is false. The
Cl--toxicity hypothesis (the apparent toxicity of
Na+ is induced by associated
Cl-) is false. The results indicate that, apart from
osmotic effects, high levels of Na+ in the rooting
medium and in the tissues are not toxic unless Ca2+
is also deficient, a condition probably leading to inadequate
compartmentation and excessive cytoplasmic accumulation. This study related
growth to ion activities at plasma-membrane surfaces. These activities were
computed by a Gouy-Chapman-Stern model then incorporated into non-linear
growth models for growth versus toxicants and ameliorants.Key
words: Calcium, potassium, salinity, sodium, toxicity
相似文献
4.
Bean plants (Phaseolus vulgaris) were very sensitive to moderate concentrations of NaCl, showing a dramatic decrease in their K+ content in the presence of this salt. Increasing the KCl content of the nutrient medium released the inhibitory effect of NaCl by increasing the K+ content of the plants. Likewise moderate concentrations of KCl were toxic for bean plants because they produced a large K+ loading. NaCl partially released this toxicity by inhibiting the K+ loading. When compared to the moderately salt tolerant sunflower plants (Helianthus annuus), bean plants showed a lower capacity to discriminate between K+ and Na+, at high Na+ levels, and an uncontrolled K+ uptake at moderate concentrations of K+. It is concluded that this low capacity of discrimination of the K+ uptake system of bean plants in presence of Na+ can account for by the NaCl sensitivity of bean plants. 相似文献
5.
Rabbit erythrocytes were exposed in vitro to continuous wave (CW) and pulse-modulated X-band microwaves in wave guide exposure chambers. Erythrocytes were exposed as whole (hep-arinized) blood suspensions or as washed cells in 1:1 isotonic buffered K+-free saline suspensions. Statistically significant increases in K+ efflux relative to thermal controls were detected when red cells were exposed in whole blood suspensions to either CW or pulsed 8.42-GHz microwaves at SARs that resulted in equilibrium sample temperatures of approximately 24 °C. Under the same exposure conditions, no statistically significant K+ efflux occurred in the case of 1:1 red cell suspensions. Measured differences in sample heating rates and temperature gradients between microwave-exposed and heated control suspensions may account in part for the differential effect of microwave exposure but such effects do not appear to explain the results of this study fully. 相似文献
6.
Molecular mechanisms of potassium and sodium uptake in plants 总被引:20,自引:0,他引:20
Potassium (K+) is an essential nutrient and the most abundant cation in plants, whereas the closely related ion sodium (Na+) is toxic to most plants at high millimolar concentrations. K+ deficiency and Na+ toxicity are both major constraints to crop production worldwide. K+ counteracts Na+ stress, while Na+, in turn, can to a certain degree alleviate K+ deficiency. Elucidation of the molecular mechanisms of K+ and Na+ transport is pivotal to the understanding – and eventually engineering – of plant K+ nutrition and Na+ sensitivity. Here we provide an overview on plant K+ transporters with particular emphasis on root K+ and Na+ uptake. Plant K+-permeable cation transporters comprise seven families: Shaker-type K+ channels, `two-pore' K+ channels, cyclic-nucleotide-gated channels, putative K+/H+ antiporters, KUP/HAK/KT transporters, HKT transporters, and LCT1. Candidate genes for Na+ transport are the KUP/HAK/KTs, HKTs, CNGCs, and LCT1. Expression in heterologous systems, localization in plants, and genetic disruption in plants will provide insight into the roles of transporter genes in K+ nutrition and Na+ toxicity. 相似文献
7.
Georg Petschenka Steffi Fandrich Nils Sander Vera Wagschal Michael Boppré Susanne Dobler 《Evolution; international journal of organic evolution》2013,67(9):2753-2761
Despite the monarch butterfly (Danaus plexippus) being famous for its adaptations to the defensive traits of its milkweed host plants, little is known about the macroevolution of these traits. Unlike most other animal species, monarchs are largely insensitive to cardenolides, because their target site, the sodium pump (Na+/K+‐ATPase), has evolved amino acid substitutions that reduce cardenolide binding (so‐called target site insensitivity, TSI). Because many, but not all, species of milkweed butterflies (Danaini) are associated with cardenolide‐containing host plants, we analyzed 16 species, representing all phylogenetic lineages of milkweed butterflies, for the occurrence of TSI by sequence analyses of the Na+/K+‐ATPase gene and by enzymatic assays with extracted Na+/K+‐ATPase. Here we report that sensitivity to cardenolides was reduced in a stepwise manner during the macroevolution of milkweed butterflies. Strikingly, not all Danaini typically consuming cardenolides showed TSI, but rather TSI was more strongly associated with sequestration of toxic cardenolides. Thus, the interplay between bottom‐up selection by plant compounds and top‐down selection by natural enemies can explain the evolutionary sequence of adaptations to these toxins. 相似文献
8.
《Trends in microbiology》2023,31(5):511-520
Several families of potassium (K+) channels are found in membranes of all eukaryotes, underlining the importance of K+ uptake and redistribution within and between cells and organs. Among them, TOK (tandem-pore outward-rectifying K+) channels consist of eight transmembrane domains and two pore domains per subunit organized in dimers. These channels were originally studied in yeast, but recent identifications and characterizations in filamentous fungi shed new light on this fungus-specific K+ channel family. Although their actual function in vivo is often puzzling, recent works indicate a role in cellular K+ homeostasis and even suggest a role in plant–fungus symbioses. This review aims at synthesizing the current knowledge on fungal TOK channels and discussing their potential role in yeasts and filamentous fungi. 相似文献
9.
Joy Perkins Geoffrey M. Gadd 《Journal of industrial microbiology & biotechnology》1995,14(3-4):218-225
Summary Toxicity screening ofEscherichia coli NCIB 9484 andBacillus subtilis 007, NCIB 168 and NCIB 1650 has shown Cs+ to be the most toxic Group 1 metal cation. However, toxicity and accumulation of Cs+ by the bacteria was affected by two main external factors; pH and the presence of other monovalent cations, particularly K+. Over the pH range 6–9 bothE. coli andB. subtilis showed increasing sensitivity towards caesium as the pH was raised. The presence of K+ and Na+ in the laboratory media used lowered caesium toxicity and lowered acumulation of the metal. In order to assess accurately Cs+ toxicity towards the bacterial strains it was therefore necessary to define the K+:Cs+ ratio in the external medium. The minimum inhibitory K+:Cs+ concentration ratio for theBacillus strains tested was in the range 12–13 whileE. coli had a minimum inhibitory K+:Cs+ concentration ratio of 16. 相似文献
10.
Two cDNAs isolated from Cymodocea nodosa, CnSOS1A, and CnSOS1B encode proteins with high-sequence similarities to SOS1 plant transporters. CnSOS1A expressed in a yeast Na+-efflux mutant under the control of a constitutive expression promoter mimicked AtSOS1 from Arabidopsis; the wild type cDNA did not improve the growth of the recipient strain in the presence of Na+, but a cDNA mutant that expresses a truncated protein suppressed the defect of the yeast mutant. In similar experiments,
CnSOS1B was not effective. Conditional expression, under the control of an arabinose responsive promoter, of the CnSOS1A and CnSOS1B cDNAs in an Escherichia coli mutant defective in Na+ efflux was toxic, and functional analyses were inconclusive. The same constructs transformed into an E. coli K+-uptake mutant revealed that CnSOS1A was also toxic, but that it slightly suppressed defective growth at low K+. Truncation in the C-terminal hydrophilic tail of CnSOS1A relieved the toxicity and proved that CnSOS1A was an excellent
low-affinity K+ and Rb+ transporter. CnSOS1B mediated a transient, extremely rapid K+ or Rb+ influx. Similar tests with AtSOS1 revealed that it was not toxic and that the whole protein exhibited excellent K+ and Rb+ uptake characteristics in bacteria. 相似文献
11.
Miller C 《Genome biology》2000,1(4):reviews0004.1-reviews00045
Potassium channels, tetrameric integral membrane proteins that form aqueous pores through which K+ can flow, are found in virtually all organisms; the genomes of humans, Drosophila, and Caenorhabditis elegans contain 30-100 K+ channel genes each. The structure of a bacterial K+ channel, sequence comparisons with other channels and electrophysiological measurements have enabled conclusions about the mechanism of gating and ion flow to be drawn for many other channels. 相似文献
12.
G. A. da Silva 《Applied microbiology and biotechnology》1996,46(2):112-121
The occurrence of killer toxins amongst yeasts in Brazilian Riesling Italico grape must was investigated by using the sensitive
strain EMBRAPA-26B as a reference strain at 18°C and 28°C. From a total of 85 previously isolated yeasts, 21 strains showed
ability to kill the sensitive strain on unbuffered grape must/agar (MA-MB) and 0.1 M citrate/phosphate-buffered yeast extract/peptone/dextrose/agar
(YEPD-MB) media both supplemented with 30 mg/l methylene blue. The killer activity of only four yeasts depended on the incubation
temperature rather than the medium used. At 28°C, the strains 11B and 53B were not able to show killer action. On the other
hand, strains 49B and 84B did not kill the sensitive yeast at 18°C. The killer strain EMBRAPA-91B and a commercial wine killer
yeast K-1 were employed to examine the sensitivity of the isolated yeasts on YEPD-MB and MA-MB at 18°C. The sensitivity and
neutral characteristics of yeasts were shown to be dependent on the medium and the killer strain. Interactions, including
K- R-, K- R+ and K+ R+ strains, simultaneously, have revealed that some K-R+ strains appear to protect the K- R- strain against the killer toxin. Sensitive dead cells, although to a less extent, also exhibited similar protection. Kinetic
studies have shown that the maximum specific growth rates were higher for the 20B YEPD-MB-sensitive strain (μmax=0.517 h-1) than for both the 91B (μmax=0.428 h-1) and K-1 (μmax= 0.466 h-1) killer strains. The protective capacity of neutral or sensitive cells that contaminate a fermentation, as well as the higher
maximum specific growth rate of sensitive yeasts, besides other factors, may preclude the dominance of a killer strain. This
protective capacity may also reduce the risk of a sensitive inoculum being killed by wild-type killer yeasts in open non-sterile
fermentation.
Received: 3 November 1995/Received revision: 11 March 1996/Accepted: 15 April 1996 相似文献
13.
Toshihiro Aiuchi Takashi Daimatsu Kazuyasu Nakaya Yasuharu Nakamura 《生物化学与生物物理学报:生物膜》1982,685(3):289-296
The intensity of rhodamine 6G fluorescence was found to be a useful scale for measuring the membrane potential in synaptosomes. The fluorescence of rhodamine 6G in synaptosomal suspensions increases with depolarization in the synaptosomes induced by the replacement of cations in the medium or by the addition of agents known to depolarize the membrane potential. Considering the character of the dye, we have derived an equation which gives the relation between the fluorescence intensity of the dye and the membrane potential. The change in membrane potential (diffusion potential) of synaptosomes was calculated using the equation. The calculated membrane potential was proportional to the logarithm of the K+ concentration above 20 mM, and the slope of membrane potential against log[K+] was about 52 mV per decade of concentration. The permeability ratio (; the ratio of the permeability constants of a given cation, X+, and K+) was estimated from the calculated membrane potential. 相似文献
14.
Mauro Gobbini Silvia Armaroli Leonardo Banfi Alessandra Benicchio Giulio Carzana Patrizia Ferrari Giuseppe Giacalone Giuseppe Marazzi Barbara Moro Rosella Micheletti Simona Sputore Marco Torri Maria Pia Zappavigna Alberto Cerri 《Bioorganic & medicinal chemistry》2010,18(12):4275-4299
We report the synthesis and biological properties of novel analogues of Istaroxime acting as positive inotropic compounds through the inhibition of the Na+,K+-ATPase. We explored the chemical space around the position 6 of the steroidal scaffold by changing the functional groups at that position and maintaining a basic oximic chain in position 3. Some compounds showed inhibitory potencies of the Na+,K+-ATPase higher than Istaroxime and many of the compounds tested in vivo were safer than digoxin, the classic digitalis compound currently used for the treatment of congestive heart failure as inotropic agent. The 3D-QSAR analyses using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) methods have been successfully applied to a set of 63 androstane derivatives as Na+,K+-ATPase inhibitors. The contour plots provide many useful insights into relationships between structural features and inhibitory potency. 相似文献
15.
Differential superoxide dismutase expression in ryegrass cultivars in response to short term aluminium stress 总被引:3,自引:0,他引:3
Cartes Paula McManus Michael Wulff-Zottele Cristián Leung Susanna Gutiérrez-Moraga Ana Mora María de la Luz 《Plant and Soil》2012,352(1-2):353-362
Background and aims
Saline soils limit plant production worldwide through osmotic stress, specific-ion toxicities, and nutritional imbalances.Methods
The ability of Ca2+ and K+ to alleviate toxicities of Na+ and Mg2+ was examined using 89 treatments in short-term (48 h) solution culture studies for cowpea (Vigna unguiculata (L.) Walp.) roots. Root elongation was related to ionic activities at the outer surface of the root plasma membrane.Results
The addition of K+ was found to alleviate the toxic effects of Na+, and supplemental Ca2+ improved growth further in these partially-alleviated solutions where K+ was present. Therefore, Na+ appears to interfere with K+ metabolism, and Ca2+ reduces this interference. Interestingly, the ability of Ca2+ to improve K-alleviation of Na+ toxicity is non-specific, with Mg2+ having a similar effect. In contrast, the addition of Ca2+ to Na-toxic solutions in the absence of K+ did not improve growth, suggesting that Ca2+ does not directly reduce Na+ toxicity in these short-term studies (for example, by reducing Na+ uptake) when supplied at non-deficient levels. Finally, K+ did not alleviate Mg2+ toxicity, suggesting that Mg2+ is toxic by a different mechanism to Na+.Conclusions
Examination of how the toxic effects of salinity are alleviated provides clues as to the underlying mechanisms by which growth is reduced. 相似文献16.
17.
Pharmacological and gene regulation properties point to the SlHAK5 K+ transporter as a system for high‐affinity Cs+ uptake in tomato plants
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Manuel Nieves‐Cordones Rosa M. Rivero Vicente Martinez Francisco Rubio 《Physiologia plantarum》2018,162(4):455-466
Potassium (K+) and cesium (Cs+) are chemically similar but while K+ is an essential nutrient, Cs+ can be toxic for living organisms, plants included. Two different situations could lead to problems derived from the presence of Cs+ in agricultural systems: (1) presence of Cs+ at high concentrations that could produce toxic effects on plants, (2) presence of micromolar concentrations of radiocesium, which can be accumulated in the plant and affect animal and human health through the food chain. While K+ uptake has been well described in tomato plants, information on molecular mechanisms involved in Cs+ accumulation in this species is absent. Here, we show that in tomato plants, high concentrations of Cs+ produce deficiency of K+ but do not induce high‐affinity K+ uptake or the gene encoding the high‐affinity K+ transporter SlHAK5. At these concentrations, Cs+ uptake takes place through a Ca2+‐sensitive pathway, probably a non‐selective cation channel. At micromolar concentrations, Cs+ is accumulated by a high‐affinity uptake system upregulated in K+‐starved plants. This high‐affinity Cs+ uptake shares features with high‐affinity K+ uptake. It is sensitive to NH4+ and insensitive to Ba2+ and Ca2+ and its presence parallels the pattern of SlHAK5 expression. Moreover, blockers of reactive oxygen species and ethylene action repress SlHAK5 and negatively regulate both high‐affinity K+ and Cs+ uptake. Thus, we propose that SlHAK5 contributes to Cs+ uptake from micromolar concentrations in tomato plants and can constitute a pathway for radiocesium transfer from contaminated areas to the food chain. 相似文献
18.
The sodium-plus-potassium ion-activated adenosine triphosphatase of cerebral microsomal fractions: treatment with disrupting agents 总被引:2,自引:2,他引:0
1. The Na+-plus-K+-stimulated adenosine triphosphatase [(Na+,K+)-ATPase] of microsomal preparations from ox brain was inactivated or diminished in activity by exposure to 2–8m-urea. Similar concentrations of urea diminished the turbidity of the suspensions. 2. Low concentrations (about 2·5mm) of NaATP with the urea gave partial or complete protection of the ATPase, without altering the concomitant change in turbidity. Some protection of the (Na+,K+)-ATPase was afforded by tris ATP, but the greatest protection was found with NaATP and in its presence the change in (Na+,K+)-ATPase with 3m-urea included a phase in which activity was enhanced by 40%. 3. The protective effect was specific to NaATP: KATP, NaADP, NaAMP and sodium pyrophosphate were without protective effect and in some cases they augmented the action of urea. 4. The turbidity of cerebral microsomal suspensions was diminished also by ultrasonic irradiation; NaATP did not alter this change. After ultrasonic treatment up to 55% of the protein and of the ATPase activity were no longer deposited by centrifugal forces of 4·5×106g-min. 5. Ultrasonic treatment and centrifugation could be carried out with little or no loss of ATPase and ammonium sulphate flocculation of the supernatant then afforded in the first material precipitated a three- to five-fold enrichment of (Na+,K+)-ATPase activity. 6. Sodium borohydride and dimethyl sulphoxide also diminished the turbidity of the microsomal fraction but enrichment of the ATPase was not effected by these reagents; ten other compounds were without action on the ATPase. 7. Acetyl phosphate was hydrolysed by the microsomal preparation and this activity was increased by added K+. Acetyl-phosphatase activity persisted in the ultrasonically treated and ammonium sulphate-fractionated preparations, which were more exacting in their requirements for K+. 8. The findings are discussed in relation to the mechanism of the (Na+,K+)-ATPase. 相似文献
19.
Digitalis-like compounds are recently identified steroids synthesized by the adrenal gland, which resemble the structure of plant cardiac glycosides. These compounds, like the plant steroids, bind to and inhibit the activity of the Na+, K+-ATPase. The possible function of the endogenous digitalis-like compounds has to be evaluated in view of the presence of different isoforms of the Na+, K+-ATPase, which differ in their sensitivity to digitalis. This review focuses on recent published data on the Na+, K+-ATPase inhibitors, the digitalis-like compounds, regarding their structure, biosynthesis and secretion from the adrenal gland, physiological role and pathological implications in diseases such as hypertension and depression. Emphasis is given to studies describing the involvement of these compounds in brain function. 相似文献
20.
Role of Potassium Channels in Amyloid-Induced Cell Death 总被引:20,自引:1,他引:19
Luis V. Colom Maria E. Diaz David R. Beers Alan Neely Wen-jie Xie Stanley H. Appel 《Journal of neurochemistry》1998,70(5):1925-1934
Abstract: Basal forebrain cholinergic neurons are severely depleted early in Alzheimer's disease and appear particularly susceptible to amyloid β-peptide (Aβ) toxicity in vivo. To model this effect in vitro, a cholinergic septal cell line (SN56) was exposed to Aβ. SN56 cells exhibited a tetraethylammonium (TEA)-sensitive outward K+ current with delayed rectifier characteristics. Increases of 64% (±19; p < 0.02) and 44% (±12; p < 0.02) in K+ current density were noted 6–12 and 12–18 h following the addition of Aβ to SN56 cell cultures, respectively. Morphological observation and staining for cell viability showed that 25 ± 4 and 39 ± 4% of SN56 cells were dead after 48- and 96-h exposures to Aβ, respectively. Perfusion of SN56 cells with 10–20 mM TEA blocked 71 ± 6 to 92 ± 2% of the outward currents, widened action potentials, elevated [Ca2+]i, and inhibited 89 ± 14 and 68 ± 14% of the Aβ toxicity. High [K+]o, which depolarizes cell membranes and increases [Ca2+]i, also protected SN56 cells from Aβ toxicity. This effect appeared specific since glucose deprivation of SN56 cells did not alter K+ current density and TEA did not protect these cells from hypoglycemic cell death. Furthermore, Aβ was toxic to a dopaminergic cell line (MES23.5) that expressed a K+ current with delayed rectifier characteristics; K+ current density was not altered by Aβ and MES23.5 cells were not protected by TEA from Aβ toxicity. In contrast, a noncholinergic septal cell line (SN48) that shows minimal outward K+ currents was resistant to the toxicity of Aβ. These data suggest that a K+ channel with delayed rectifier characteristics may play an important role in Aβ-mediated toxicity for septal cholinergic cells. 相似文献