Metabolism of benzalphthalide by Pseudomonas sp.

A Pseudomonas sp. degraded benzalphthalide to o-phthalate and benzoate. A tentative pathway for the metabolism of benzalphthalide in this Pseudomonas sp. is proposed on the basis of isolated metabolites, oxygraphic assay and enzymatic studies.     

Internode length in Zea mays L.

[¹³C, ³H]Gibberellin A₂₀ (GA₂₀) has been fed to seedlings of normal (tall) and dwarf-5 and dwarf-1 mutants of maize (Zea mays L.). The metabolites from these feeds were identified by combined gas chromatography-mass spectrometry. [¹³C, ³H]Gibberellin A₂₀ was metabolized to [¹³C, ³H]GA₂₉-catabolite and [¹³C, ³H]GA₁ by the normal, and to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₁ by the dwarf-5 mutant. In the dwarf-1 mutant, [¹³C, ³H]GA₂₀ was metabolized to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₂₉-catabolite; no evidence was found for the metabolism of [¹³C, ³H]GA₂₀ to [¹³C, ³H]GA₁. [¹³C, ³H]Gibberellin A₈ was not found in any of the feeds. In all feeds no dilution of ¹³C in recovered [¹³C, ³H]GA₂₀ was observed. Also in the dwarf-5 mutant, the [¹³C]label in the metabolites was apparently undiluted by endogenous [¹³C]GAs. However, dilution of the [¹³C]label in metabolites from [¹³C, ³H]GA₂₀ was observed in normal and dwarf-1 seedlings. The results from the feeding studies provide evidence that the dwarf-1 mutation of maize blocks the conversion of GA₂₀ to GA₁.Abbreviations GA_n gibberellin A_n - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - RP reverse phase     

Metabolism of [13C1]gibberellin A29 to [13C1]gibberellin-catabolite in maturing seeds of Pisum sativum cv. Progress No. 9

The metabolism of GA₂₉ during seed maturation in Pisum sativum cv. Progress No. 9 was further investigated. [17-¹³C₁]GA₂₉ was metabolised to a GA-catabolite (structure 3), with incorporation of the [¹³C] label from the GA₂₉ substrate into the GA-catabolite being demonstrated by GC-MS. Quantitation of the GA-catabolite using GC-MS was achieved by adding GA-catabolite, labelled with [¹⁸O], to seed extracts as an internal standard. At least 50% conversion of [¹³C₁]GA₂₉ to [¹³C₁]GA-catabolite was demonstrated with the build up of exogenous [¹³C₁]GA-catabolite strictly paralleling the accumulation of native GA-catabolite. These results strongly suggest that conversion of GA₂₉ to the GA-catabolite is a natural metabolic step occurring during the final stages of seed maturation. 25 g per seed of native GA-catabolite was recorded in 37 day old seeds. Some problems encountered in the analysis of extracts containing the GA-catabolite are discussed briefly.Abbreviations BSTFA bis(trifluoromethylsilyl)acetamide - GA_n gibberellin A_n - GC gas chromatography - GC-MS combined gas chromatography-mass spectrometry - Me methyl ester - SICM selected ion current monitoring - TMSi trimethylsilyl ether     

The quantitative relationship between gibberellin A1 and internode growth in Pisum sativum L.

The metabolism and growth-promoting activity of gibberellin A₂₀ (GA₂₀) were compared in the internode-length genotypes of pea, na le and na Le. Gibberellin A₂₉ and GA₂₉-catabolite were the major metabolites of GA₂₀ in the genotype na le. However, low levels of GA₁, GA₈ and GA₈-catabolite were also identified as metabolites in this genotype, confirming that the le allele is a leaky mutation. Gibberellin A₂₀ was approximately 20 to 30 times as active in promoting internode growth of genotype na Le as of genotype na le. However, the levels of the 3-hydroxylated metabolite of GA₂₀, GA₈ (2-hydroxy GA₁), were similar for a given growth response in both genotypes. In each case a close linear relationship was observed between internode growth and the logarithm of GA₈ levels. A similar relationship was found on comparing GA₂₀ metabolism in the three genotypes le ^d, le and Le. The former mutation results in a more severe dwarf phenotype than the le allele (which has previously been shown to reduce the 3-hydroxylation of GA₂₀ to GA₁). These results indicate that GA₂₀ has negligible intrinsic activity and support the contention that GA₁ is the only GA active per se in promoting stem growth in pea.Abbreviations GA_n gibberellin A_n - GC-MS gas chromatography-mass spectrometry - HPLC high-pressure liquid chromatography     

Different endogenous cytokinins between male and female Mercurialis annua L.

The endogenous pool of cytokinin metabolites during sexual differentiation of Mercurialis annua L. was studied with a computerized gas-chromatography-mass spectrometry system. Certain metabolites were common to both sexes: ribosides (isopentenyl-adenosine, ribosylzeatin) and the nucleotide of I₆-Ade. Zeatin could be detected only in females while its nucleotide was present in males. The results were obtained with differentiating apices and whole plants. The high Z concentration and the low level of its nucleotide are related to the absence of two dominant complementary genes, determining maleness. Study of the regulation of cytokinin metabolism now seems possible.Abbreviations IPA isopentenyl adenosine - I₆-Ade isopentenyl adenine - Z zeatin - RZ ribosylzeatin     

Heterotrophic metabolism and diazotrophic growth ofNostoc sp. fromCycas circinalis

The cyanobiont ofCycas circinalis (identified asNostoc sp.) was isolated and its heterotrophic metabolism was studied in free culture under nitrogen-fixing conditions. Morphology, growth rate, nitrogenase activity, biochemical composition, efficiency of assimilation of organic carbon and molecular nitrogen were determined under different conditions of energy and carbon supply. The study has revealed the high potential of the heterotrophic metabolism in this symbiotic cyanobacterium. Although low rates of metabolic activities were attained under heterotrophic conditions, the efficiencies of organic carbon utilization (0.48 g cell-carbon per g glucose-carbon in chemoheterotrophy, from 0.65 to 0.74 under photoheterotrophy) and of N₂ assimilation (35.0 mg N₂ fixed per g glucose used in chemoheterotrophy, from 58.3 to 61.9 under photoheterotrophy) displayed by this organism were among the highest ever found in diazotrophically grown microorganisms. The isolate fromC. circinalis was able to grow indefinitely in the dark under nitrogen-fixing conditions, maintaining a well balanced biosynthetic activity and the capacity to resume photosynthetic metabolism quickly. The significance of the heterotrophic potential of this symbioticNostoc is discussed.     

Microbial Metabolism of Quinoline by Comamonas sp.

An aerobic bacterial strain which can use quinoline as the sole carbon and energy source has been isolated from activated sludge and identified as Comamonas sp. The microbial metabolism of quinoline by this strain has been investigated. A pH 8 and a temperature of 30 °C were the optimum degradation conditions of quinoline. Five intermediates including 2-oxo-1,2-dihydroquinoline, 5-hydroxy-6-(2-carboxyethenyl)-1H-2-pyridone, 6-hydroxy-2-oxo-1,2-dihydroquinoline, 5,6-dihydroxy-2-oxo-1,2-dihydroquinoline, and 8-hydroxy-2-oxo-1,2-dihydroquinoline were found during quinoline biodegradation. The presence of these intermediates suggested that at least two pathways were involved for quinoline degradation by Comamonas sp. and a reasonable degradation route was proposed to account for the intermediates observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

A light-enhanced metabolism of sulfite in cells of Cucumis sativus L. cotyledons

The effects of light and several photosynthetic inhibitors on the rate of sulfite metabolism in cells obtained from Cucumis sativus L. cotyledons was studied. The cells were treated with 200 M Na₂SO₃ and the disappearance of sulfite was monitored using either dithiobisnitrobenzoic acid or fuchsin. The rate of sulfite disappearance in light was double the dark rate. Disalicylidene propanediamine at 1 mM increased this light-enhanced metabolism approx. 50%; neither 1 M 3,4-dichlorophenyl-N,N-dimethylurea nor 0.1 mM cyanazine, which completely inhibited CO₂-dependent oxygen evolution, affected the rate of sulfite metabolism. Addition of 200 M Na₂SO₃ to the cells partially inhibited ¹⁴CO₂ fixation. The rate of sulfite consumption by the cells did not affect this inhibition. We conclude that light-dependent sulfite metabolism is cucumber cells may utilize reduced ferredoxin generated as a result of photosynthetic electron transport. An injurious interaction between CO₂ fixation and sulfite appears to occur independently of the sulfite-metabolism process.Abbreviations DCMU 3,4-dichlorophenyl-N,N-dimethylurea - DSPD disalicylidene propanediamine - DTNB 5,5-dithiobis-(2-nitrobenzoic acid)     

Characterization of carbon metabolism in Opuntia ficus-indica Mill. exhibiting the idling mode of Crassulacean acid metabolism

Upon transfer from well-watered conditions to total drought, long-day-grown cladodes of Opuntia ficus-indica Mill. shift from full Crassulacean acid metabolism (CAM) to CAM-idling. Experiments using ¹⁴C-tracers were conducted in order to characterize the carbon-flow pattern in cladodes under both physiological situations. Tracer was applied by ¹⁴CO₂ fumigations and NaH¹⁴CO₃ injections during the day-night cycle. The results showed that behind the closed stomata, mesophyll cells of CAM-idling plants retained their full capacity to metabolize CO₂ in light and in darkness. Upon the induction of CAM-idling the level of the capacity of phosphoenolpyruvate carboxylase (EC 4.1.1.31) was maintained. By contrast, malate pools decreased, displaying finally only a small or no day-night oscillation. The capacity of NADP-malic enzyme (EC 1.1.1.40) decreased in parallel with the reduction in malate pools. Differences in the labelling patterns, as influenced by the mode of tracer application, are discussed.Abbreviations CAM Crassulacean acid metabolism - PEP-Case phosphoenolpyruvate carboxylase     

Effects of ammonia on carbon metabolism in photosynthesizing isolated mesophyll cells from Papaver somniferum L.

Addition of ammonia to a suspension of photosynthesizing isolated mesophyll cells from P. somniferum quantitatively alters the pattern of carbon metabolism by increasing rates of certain key ratelimiting steps leading to amino-acid synthesis and by decreasing rates of rate-limiting steps in alternative biosynthetic pathways. Of particular importance is the stimulation of reactions mediated by pyruvate kinase and phosphoenolpyruvate carboxylase. The increased rates of these two reactions, which result in an increased flow of carbon into the tricarboxylic-acid cycle, correlate with a rapid rise in glutamine (via glutamine synthetase) which draws carbon off the tricarboxylic-acid cycle as -ketoglutarate. Increased flux of carbon in this direction appears to come mainly at the expense of sucrose synthesis. The net effect of addition of ammonia to mesophyll cells is thus a redistribution of newly fixed carbon away from carbohydrates and into amino acids.     

Ethylene metabolism in Pisum sativum L.

The possible role of C₂H₄ metabolism in mediating the responses of plants to C₂H₄ is re-examined. It is demonstrated that (i) the effects of inhibitors upon C₂H₄ action do not correspond with their effects on metabolism, (ii) elicitors of C₂H₄ effects do not have appropriate effects on C₂H₄ metabolism, (iii) inhibitors of C₂H₄ metabolism do not affect the response of plants to C₂H₄. It is concluded that metabolism of C₂H₄ is not linked to the mode of action of the growth regulator.Abbreviations DTC sodium diethyldithiocarbamate - FW fresh weight     

Nickel and the metabolism of urea by Lemna paucicostata Hegelm. 6746

With urea as sole nitrogen source, the addition of 5×10^-5 M nickel sulfate to axenic cultures of Lemna paucicostata 6746 approximately doubles the rate of vegetative growth. Under a standard light-dark schedule, Ni²⁺ changes the daily pattern of respiratory CO₂ output on urea from one having a single daily peak to one with two daily peaks which resembles that on ammonium or nitrate as sole nitrogen source. It also increases CO₂ output by as much as 3-fold on a fresh-weight basis. These data represent the first confirmation in an intact higher plant of proposals, based on enzymology and tissue culture responses, for a role of Ni²⁺ in urea metabolism. Further, they indicate the possible existence of two distinct pathways of urea utilization.     

Oleate metabolism in microsomes from developing leaves ofPisum sativum L.

Microsomes from young leaves of pea,Pisum sativum L., metabolized oleate principally by the reactions mediated by oleoyl-CoA synthetase, oleoyl-CoA thioesterase, oleoyl-CoA: phosphatidylcholine acyltransferase and oleoyl phosphatidylcholine desaturase. Hydrogen peroxide specifically inhibited oleate desaturation and the evidence presented argues for a specific inhibition of the terminal enzyme of the desaturase system, i.e. oleoyl phosphatidylcholine desaturase. Catalase, ascorbic acid, or ascorbate peroxidase, in conjunction with ascorbic acid, stimulated oleate desaturation, possibly by the removal of hydrogen peroxide. Lysophosphatidylcholine was found to be the preferred acceptor for acyl transfer from oleoyl-CoA, which indicates that the transfer of oleoyl moieties was catalyzed predominantly by oleoyl-CoA:lysophosphatidylcholine acyltransferase. Acyl exchange between oleoyl-CoA and phosphatidylcholine, with a possible involvement of phospholipases, was also detected but at much lower rates than acyl transfer. When intact or broken chloroplasts were added to microsomes, which had been preincubated with oleoyl-CoA, some stimulation of the reactions catalyzed by oleoyl-CoA:phosphatidylcholine acyltransferase and oleoyl phosphatidylcholine desaturase was observed. However, only minor amounts of microsomal linoleoyl phosphatidylcholine were converted to galactolipids containing linolenoyl moieties.Abbreviations FA unesterified fatty acid (s) - PC phosphatidylcholines - 18:1 oleoyl moieties - 18:2 lmoleoyl moieties Dedicated to Professor Helmut K. Mangold, Bundesanstalt für Fettforschung, Münster, on his 60th birthday     

Waterlogging responses of Sporobolus virginicus (L.) Kunth.

Summary Flooding responses in Sporobolus virginicus (L.) Kunth., a perennial C₄ grass, propagated from plants collected on the fringes of a mangrove swamp, were examined in a glasshouse study over 42 days. Flooding significantly reduced soil redox potential, induced adventitious root development, shifted resource allocation from below- to above-ground components without affecting total biomass accumulation and significantly decreased below-ground/above-ground biomass ratios. Although soil waterlogging significantly increased alcohol dehydrogenase activity (ADH) after 30 h, significant increase in central air space by 45–50% of the cross-sectional stem area eliminated root hypoxia, and ADH activity decreased to levels equivalent to drained controls after 42 days. In addition, flooded plants exhibited significantly higher carbon dioxide assimilation rates but similar relative growth rates (RGR) to drained controls. The results indicate that S. virginicus responds to water-logging by a combination of metabolic, morphological and anatomical mechanisms, which may account for its widespread distribution in coastal lagoons, estuaries and marshes.     

Biosynthesis and metabolism of indole-3-ethanol and indole-3-acetic acid by Pinus sylvestris L. needles

Combined gas chromatography-mass spectrometry has been used to identify indole-3-ethanol (IEt) in a purified extract from needles of Pinus sylvestris L. Quantitative estimates obtained by high-performance liquid chromatography with fluorescence detection, corrected for samples losses occurring during purification, indicate that Pinus needles contain 46±4 ng g^-1 IEt. This compares with 24.5±6.5 ng g^-1 indole-3-acetic acid (IAA) and 2.3±0.4 ng g^-1 indole-3-carboxylic acid (ICA) (Sandberg et al. 1984, Phytochemistry, 23, 99–102). Metabolism studies with needles incubated in a culture medium in darkness revealed that both [3-¹⁴C]-tryptophan and [2-¹⁴C]tryptamine mine are converted to [¹⁴C]IEt. It was also shown that [3-¹⁴C]IEt acted as a precursor of [¹⁴C]IAA. The observed metabolism appears to be enzymic in nature. The [2-¹⁴C]IAA was not catabolised to [¹⁴C]ICA in detectable quantities implying that, at best, only a minor portion of the endogenous ICA pool in the Pinus needles originates from IAA.Abbreviations DEAE diethylaminoethyl - GC-MS gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - IAA indole-3-acetic acid - ICA indole-3-carboxylic acid - IEt indole-3-ethanol - PVP polyvinylpyrrolidone     

Effects of molybdenum on ascorbate-glutathione cycle metabolism in Chinese cabbage (Brassica campestris L. ssp. pekinensis)

A hydroponic trial was conducted to investigate effects of molybdenum (Mo) on ascorbate-glutathione cycle (AsA-GSH cycle) metabolism in Chinese cabbage (Brassica campestris L. ssp. pekinensis). Mo was applied at four rates: 0, 0.01, 0.15 and 1.5 mg l⁻¹. The concentrations of ascorbate, dehydroascorbate, reduced- and oxidized- glutathione, and activities of five key enzymes in the AsA-GSH cycle were studied. The results showed that appropriate Mo application increased the fresh weight of Chinese cabbage, but excess application of Mo (1.5 mg l⁻¹ Mo) decreased the fresh weight. Total ascorbate and reduced ascorbate concentrations in the Chinese cabbage increased with Mo application rates. Although no significant differences existed in DHA concentration between the different Mo regimes, but it has an increase trend with the 0.01 mg l^-1 Mo treatment, and then decreased with the Mo level increasing. No significant difference in GSH concentration was found between the different Mo treatments. Compared with the control, the GSSG concentration decreased significantly in the 0.01 mg l⁻¹ Mo treatment. The activities of APX, MDHAR, DHAR and GR increased due to Mo application. But the activity of AAO decreased with increasing Mo application rates. It is hypothesized that Mo may promote the redox process and regeneration of ascorbic acid, and affect the ability of anti-oxidation in the Chinese cabbage. Responsible Editor: Jian Feng Ma.     

Nocturnal stachyose metabolism in leaf tissues of Xerosicyos danguyi H. Humb.

Leaf discs obtained from mature leaves of Xerosicyos danguyi were found to contain appreciable levels of stachyose throughout an 8-h nocturnal period during which this plant performs Crassulacean acid metabolism (CAM). In contrast, in mesophyll tissues obtained from paradermal sections of these same leaf discs and which were devoid of vascular tissues, stachyose pools were rapidly depleted during the nocturnal phase. The pattern of this depletion followed closely the depletion pattern observed for starch, indicating that mesophyll stachyose was possibly involved in nocturnal CAM processes and was not necessarily being used for export. Pulse-labelling of intact X. danguyi leaves prior to excision of leaf discs and mesophyll samples also indicated that, while labelled stachyose had turned-over completely in the mesophyll tissues by the end of the nocturnal period, substantial levels of labelled stachyose were always recovered from the leaf discs from which these mesophyll samples were derived. The data indicate the existence of two separate pools of stachyose in the X. danguyi leaf, one a mesophyll pool which turns over rapidly at night and which may be involved to a small extent in nocturnal CAM processes, and the other a pool associated with and possibly synthesized by the vascular tissues and which presumably represents the phloem-transport pool.Abbreviation CAM Crassulacean acid metabolism This work was supported by National Science Foundation Grant DCB 8901785.