共查询到20条相似文献,搜索用时 78 毫秒
1.
2.
3.
4.
5.
6.
7.
8.
9.
Bacterial Metabolism of 3-Hydroxy-3-Methylglutaric Acid 总被引:1,自引:0,他引:1
An organism belonging to Pseudomonadaceae and capable of utilizing 3-hydroxy-3-methylglutarate as sole carbon source has been isolated from soil. Whole-cell preparations catalyze the oxidation of acetoacetate, acetate, glyoxylate, and citric acid cycle intermediates. Cell-free extracts of 3-hydroxy-3-methylglutarate-grown cells show an adenosine triphosphate, coenzyme A (CoA), and Mg(2+)-dependent conversion of 3-hydroxy-3-methylglutarate to 3-hydroxy-3-methylglutaryl-CoA. Succinyl-CoA-generating system has no effect on the activation and catabolism of 3-hydroxy-3-methylglutarate. 相似文献
10.
The biological activity of 20 l-alpha-amino acid conjugates of indole-3-acetic acid (IAA) to stimulate cell elongation of Avena sativa coleoptile sections and to stimulate growth of soybean cotyledon tissue cultures has been examined at concentrations of 10(-4) to 10(-7)m. In the Avena coleoptile test, most of the amino acid conjugates stimulated elongation. Several of the conjugates stimulated as much elongation as IAA but their half-maximum concentrations tended to be higher. Some of the more active conjugates were alanine, glycine, lysine, serine, aspartic acid, cystine, cysteine, methionine, and glutamic acid.In the soybean cotyledon tissue culture test, all of the l-alpha-amino acid conjugates of IAA stimulated growth except for the phenylalanine, histidine, and arginine conjugates. Most of the conjugates produced responses at least as great as that caused by IAA. Conjugates with half-maximum concentrations lower than IAA included cysteine, cystine, methionine, and alanine. These conjugates exceed the IAA-induced callus growth at all tested concentrations. Other conjugates significantly better than IAA at 10(-6)m were serine, glycine, leucine, proline, and threonine. 相似文献
11.
Anders ?stin Mariusz Kowalyczk Rishikesh P. Bhalerao G?ran Sandberg 《Plant physiology》1998,118(1):285-296
The metabolism of indole-3-acetic
acid (IAA) was investigated in 14-d-old Arabidopsis plants grown in
liquid culture. After ruling out metabolites formed as an effect of
nonsterile conditions, high-level feeding, and spontaneous
interconversions, a simple metabolic pattern emerged. Oxindole-3-acetic
acid (OxIAA), OxIAA conjugated to a hexose moiety via the carboxyl
group, and the conjugates indole-3-acetyl aspartic acid (IAAsp) and
indole-3-acetyl glutamate (IAGlu) were identified by mass spectrometry
as primary products of IAA fed to the plants. Refeeding experiments
demonstrated that none of these conjugates could be hydrolyzed back to
IAA to any measurable extent at this developmental stage. IAAsp was
further oxidized, especially when high levels of IAA were fed into the
system, yielding OxIAAsp and OH-IAAsp. This contrasted with the
metabolic fate of IAGlu, since that conjugate was not further
metabolized. At IAA concentrations below 0.5 μm, most of
the supplied IAA was metabolized via the OxIAA pathway, whereas only a
minor portion was conjugated. However, increasing the IAA
concentrations to 5 μm drastically altered the metabolic
pattern, with marked induction of conjugation to IAAsp and IAGlu. This
investigation used concentrations for feeding experiments that were
near endogenous levels, showing that the metabolic pathways controlling
the IAA pool size in Arabidopsis are limited and, therefore, make good
targets for mutant screens provided that precautions are taken to avoid
inducing artificial metabolism.The plant hormone IAA is an important signal molecule in the
regulation of plant development. Its central role as a growth regulator
makes it necessary for the plant to have mechanisms that strictly
control its concentration. The hormone is believed to be active
primarily as the free acid, and endogenous levels are controlled in
vivo by processes such as synthesis, oxidation, and conjugation. IAA
has been shown to form conjugates with sugars, amino acids, and small
peptides. Conjugates are believed to be involved in IAA transport, in
the storage of IAA for subsequent use, in the homeostatic control of
the pool of the free hormone, and as a first step in the catabolic
pathways (Cohen and Bandurski, 1978; Nowacki and Bandurski, 1980;
Tuominen et al., 1994; Östin et al., 1995; Normanly, 1997). It is
generally accepted that in some species conjugated IAA is the major
source of free IAA during the initial stages of seed germination (Ueda
and Bandurski, 1969; Sandberg et al., 1987; Bialek and Cohen, 1989),
and there is also evidence that in some plants (but not all; see Bialek
et al., 1992), the young seedling is entirely dependent on the release
of free IAA from conjugated pools until the plant itself is capable of
de novo synthesis (Epstein et al., 1980; Sandberg et al., 1987).The function of conjugated IAA during vegetative growth is somewhat
less clear. It has been shown that conjugated IAA constitutes as much
as 90% of the total IAA in the plant during vegetative growth
(Normanly, 1997). However, the role of the IAA conjugates at this stage
of the plant''s life cycle remains unknown. Analysis of endogenous IAA
conjugates in vegetative tissues has revealed the presence of a variety
of different compounds, including indole-3-acetyl-inositol,
indole-3-acetyl-Ala, IAAsp, and IAGlu (Anderson and Sandberg, 1982;
Cohen and Baldi, 1983; Chisnell, 1984; Cohen and Ernstsen, 1991;
Östin et al., 1992). Studies of vegetative tissues have indicated
that IAAsp, one of the major conjugates in many plants, is the first
intermediate in an irreversible deactivation pathway (Tsurumi and Wada,
1986; Tuominen et al., 1994; Östin, 1995). Another mechanism that
is believed to be involved in the homeostatic control of the IAA pool
is catabolism by direct oxidation of IAA to OxIAA, which has been shown
to occur in several plant species (Reinecke and Bandurski, 1983;
Ernstsen et al., 1987).One area in the study of IAA metabolism in which our knowledge is
increasing is the analysis of the homeostatic controls of IAA levels in
plants. It has been possible, for instance, to increase the levels of
IAA in transgenic plants expressing iaaM and iaaH
genes from Agrobacterium tumefaciens. Analysis of these
transgenic plants has indicated that plants have several pathways that
can compensate for the increased production of IAA (Klee et al., 1987;
Sitbon, 1992). It is expected that future studies using now-available
genes will provide further insight into IAA metabolism. For example, a
gene in maize encoding IAA-Glc synthetase has been identified, and
several genes (including ILR1, which may be involved
in hydrolysis of the indole-3-acetyl-Leu conjugate) have been cloned
from Arabidopsis (Szerszen et al., 1994; Bartel and Fink,
1995). Furthermore, Chou et al. (1996) identified a gene that
hydrolyzes the conjugate IAAsp to free IAA in the bacterium
Enterobacter aggloremans.Because of its small genome size, rapid life cycle, and the ease of
obtaining mutants, Arabidopsis is increasingly used as a
genetic model system to investigate various aspects of plant growth and
development. IAA signal transduction is also being investigated
intensively in Arabidopsis in many laboratories (Leyser, 1997). Mutants
with altered responses to externally added auxins or IAA conjugates
have been identified in Arabidopsis. The identified mutants are either
signal transduction mutants such as axr1-4 (Lincoln et al.,
1990), or have mutations in genes involved in auxin uptake or
transport, such as aux1 and pin1 (Okada et al.,
1991; Bennett et al., 1996). A few mutants that are unable to regulate
IAA levels or are unable to hydrolyze IAA conjugates, sur1-2
and ilr1, respectively, have also been identified (Bartel
and Fink, 1995; Boerjan et al., 1995). To our knowledge, no mutant that
is auxotrophic for IAA has been identified to date, which may
reflect the redundancy in IAA biosynthetic pathways or the lethality of
such mutants.In spite of the work reported thus far, many aspects of the metabolism
of IAA in Arabidopsis require further investigation, because few
details of the processes involved in IAA regulation are known. This
lack of knowledge puts severe constraints on genetic analysis of IAA
metabolism in Arabidopsis. For example, it is essential to have prior
knowledge of IAA metabolism to devise novel and relevant screens with
which to identify mutants of IAA metabolism. We have sought to address
this issue by identifying the metabolic pathways involved in catabolism
and conjugation under conditions that minimally perturb physiological
processes. In this investigation we studied the conjugation and
catabolic pattern of IAA by supplying relatively low levels of labeled
IAA and identifying the catabolites and conjugates by MS. Different
feeding systems were tested to optimize the application of IAA and to
avoid irregularities in metabolism attributable to culturing, feeding
conditions, or microbial activity. It is well documented that IAA
metabolism is altered according to the amount of exogenous auxin
applied; therefore, we placed special emphasis on distinguishing
between catabolic routes that occur at near-physiological
concentrations and those that occur at the high auxin concentrations
commonly used in mutant screens. 相似文献
12.
The nature of metabolic products of 3indolylacetic acid(IAA) extracted from potato tuber disks treated with aeratedIAA solution has been investigated. Two major products, knownat first as V and P in these studieshave been isolated and V has been identified as3-indolylacetylaspartic acid (IacAsp). The rapid uptake of IAA is inhibitited by metabolic poisonssuch as 103 M. cyanide. The maximum mean internal concentrationexceeds the external concentration wellaerated cultures.The mean internal concentration, however only remains for aperiod and then falls off rapidly as a result of extrusion ofabsorbed IAA into the external solution. This extrusion is notinhibited by 10-3 cyanide; when the mean internal IAA concentrationis 150 µ mol/ml. and the localized IAA concentration musttherefore exceed this value. We conclude therefore that theIAA concentration in the sites where it has accumulated exceedsthe concentration of IAA outside. Uptake of IAA and also its further conversion are inhibitedby indolylacetonitrile and promoted by aspartate, but this promotionis not associated with any gain in amount of indolylacetylaspartate(IacAsp). The data suggest that IacAsp may be formed in tissue from boundIAA rather then free IAA. The accelerator found in potato and beans whichhas similar RF to IAcAsp has been shown definity to be someother substance or substances and not IAcAsp as was at firstthought possible. 相似文献
13.
Crassulacean Acid Metabolism and Crassulacean Acid Metabolism Modifications in Peperomia camptotricha 总被引:9,自引:6,他引:3
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Peperomia camptotricha, a tropical epiphyte from Mexico, shows variable forms of Crassulacean acid metabolism (CAM). Young leaves exhibit CAM-cycling, while mature leaves show an intermediate type of metabolism, between CAM and CAM-cycling, having approximately the same amount of nighttime gas exchange as daytime. Metabolism of young leaves appears independent of daylength, but mature leaves have a tendency toward more CAM-like metabolism under short days (8 hours). Large differences in the physical appearance of plants were found between those grown under short daylengths and those grown under long daylengths (14 hours). Some anatomical differences were also detected in the leaves. Water stress caused a switch to CAM in young and mature leaves, and as water stress increased, they shifted to CAM-idling. 相似文献
14.
15.
Anoxic stress induces a strong change in sugar, protein, and amino acid metabolism in higher plants. Sugars are rapidly consumed through the anaerobic glycolysis to sustain energy production. Protein degradation under anoxia is a mechanism to release free amino acids contributing in this way to maintaining the osmotic potential of the tissue under stress. Among free amino acids, a particular role is played by glutamic acid, being a precursor of some characteristic compounds of the anaerobic metabolism (alanine, -aminobutyric acid, and putrescine). The glutamine synthetase/glutamate synthase cycle contributes to ammonia reassimilation and primary assimilation of nitrate, and resynthesizes constantly glutamate for the synthesis of other compounds. Some polypeptides involved in these pathways are expressed under anoxia. The importance of amino acid metabolism for the response to anaerobic stress is discussed. 相似文献
16.
17.
18.
氨基酸代谢与肝性脑病 总被引:2,自引:1,他引:1
肝性脑病 (HepaticEncephalopathy)又称肝昏迷 ,即由于严重肝病引起的中枢神经系统功能紊乱 ,患者出现一系列神经精神病状 ,直至进入昏迷。在此仅从氨基酸代谢异常的角度叙述与肝性脑病的关系。 相似文献
19.
Investigations on the Mechanism of the Brassinosteroid Response: I. Indole-3-acetic Acid Metabolism and Transport 总被引:9,自引:7,他引:2
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A brassinosteroid treatment of light-grown first internode sections of Phaseolus vulgaris results in an increased bending response following unilateral indole-3-acetic acid (IAA) application. Reverse isotope dilution analysis shows that this increased response is not due to an increase in the concentration of applied IAA in the tissue or a change in the amount of IAA conjugated. Treatment with the brassinosteroid also does not affect the rate of IAA transport as measured using the agar block method. These results indicate that even though brassinosteroid potentiates auxin action, it does not have a direct effect on IAA uptake, metabolism, or cell to cell transport. 相似文献
20.
Soluble cell-free extracts of actinomycete S4 grown on media containing mevalonate catalyze acetoacetate formation from mevalonate, mevaldate, and β-hydroxy-β-methylglutaryl-coenzyme A (CoA). Conversion of mevalonate to acetoacetate involves formation of free β-hydroxy-β-methylglutaryl-CoA, but not free mevaldate. The reaction favors mevalonate oxidation, and nicotinamide adenine dinucleotide, rather than nicotinamide adenine dinucleotide phosphate, acts as oxidant. 相似文献