Constituants volatils de Lycopersicon esculentum

The volatile components of the tomato have been studied by combined GC-MS with and without previous separation by preparative GC. 5-Methylfurfuryl ketone, furfuryl alcohol, p-anisaldehyde, p-vinylphenol and geraniol were identified and 2-methyl-2-pentanol, 2-heptanol, 4-heptanol, trans-3-hexene-1-ol and trans-2-hexene-1-ol, sec-butyl butyrate, lactone of 5,6-dihydroxyhexanoic acid and isopropyl anisole were tentatively identified.     

Carotene epoxides of Lycopersicon esculentum

A series of oxygenated carotenoids has been isolated from tomatoes. Two of these compounds have been identified, by comparison of their chromatographic and spectroscopic properties with those of semisynthetic samples, as epoxides of lycopene (1,2-epoxy-1,2-dihydro-ψ,ψ-carotene and 5,6-epoxy-5,6-dihydro-ψ,ψ-carotene). The other related compounds have been identified by their chromatographic, spectroscopic and chemical properties as mutatochrome (5,8-epoxy-5,8-dihydro-β,β-carotene) and epoxides of phytoene (1,2-epoxy-1,2,7,8,11,12,7′,8′,11′,12′-decahydro-ψ, ψ-carotene), phytofluene (1,2-epoxy-1,2,7,8, 11,12,7′,8′-octahydro-ψ,ψ-carotene and 1,2-epoxy-1,2,7,8,7′,8′,11′,12′-octahydro-ψ,ψ-carotene) and ξ-carotene (1,2-epoxy-1,2,7,8,7′,8′-hexahydro-ψ,ψ-carotene). The presence in tomatoes of apo-6′-lycopenal (6′-apo-ψ-caroten-6′-al), 8′-apo-lycopenal (8′-apo-ψ-caroten-8′-al) and lycoxanthin (ψ,ψ-caroten-16-ol) has been confirmed by comparison with authentic samples.     

Purification and properties of phosphofructokinase from fruits of Lycopersicon esculentum

A procedure is described using affinity chromatography on Blue Sepharose and on an immobilized ATP column by which phosphofructokinase has been purified by 260-fold from tomato fruits. The properties of the enzyme are affected by the pH at which the preparation is made and maintained. At the pH optimum, pH 8.0, the enzyme is very heterogeneous with up to three forms present differing in MW. At pH 7.5 a single major form of MW 180 000 is present, and evidence that raising the pH to 8.0 promotes dissociation of the enzyme is discussed.     

Electrophoretic investigation of enzymes from developing Lycopersicon esculentum fruit

Acetone powders were prepared from tomato fruit tissue sampled during development and the proteins were separated by polyacrylamide disc gel electrophoresis. The gels were stained to show up general proteins, lipoproteins, glycoproteins and certain enzymes. Minor changes in protein and glycoprotein patterns accompanied development. Most enzymes exhibited more than one active band, with maximum diversity and specific activities usually appearing in extracts from mature green tissue and least with over-ripe tissue. The results support the view that enzyme synthesis accompanies the climacteric respiration rise at the expense of non-metabolic protein.     

Pigment evolution in Lycopersicon esculentum fruits during growth and ripening

During growth and subsequent maturation, the distribution and formation of pigments in the inner pulp and in the outer region of the pericarp of ‘che     

Effect of potassium nutrition on some enzymes from ripening Lycopersicon esculentum fruit

The maximum respiration rate of tomato fruit during the climacteric period was markedly increased when the plants were grown under potassium-deficient conditions. Whereas potassium deficiency had no effect on cytoplasmic glutamate-oxoloacetate transaminase, there was a significant increase in the activity of this enzyme from mitochondria once the fruit began to change colour. Malate dehydrogenase was reduced in activity by potassium deficiency. It is suggested that the augmented mitochondrial transiminase levels, coupled with reduced malate dehydrogenase activity in low potassium fruit, result in reduced levels of oxaloacetic acid which is a potent inhibitor of Krebs cycle oxidations, thus leading to higher respiration rates for the intact fruit.     

Sucrose absorption and synthesis by excised Lycopersicon esculentum roots

Asymmetrically-labelled sucrose was absorbed intact by excised roots of tomato, grown in sucrose. Glucose-grown roots possessed sucrose synthetase and sucrose phosphate synthetase activity.     

Glutamate oxaloacetate transaminase activity in developing Lycopersicon esculentum fruit

Glutamate oxaloacetate transaminase (GOT) occurs in both the mitochondrial and cytoplasmic fractions from tomato fruit tissue. Changes in activity of the enzyme from fruit at selected developmental stages have been followed. The combined activity fell from the immature green stage to the full red condition whilst the proportion in the mitochondria reached a peak in green-orange fruit. The activity of cytoplasmic, but not mitochondrial, GOT was stimulated by the addition of pyridoxal-5-phosphate. In the green areas of fruit showing blotchy ripening, the combined activity was equivalent to that in normal immature green fruit but with a much higher proportion of the activity in the mitochondria. Mitochondrial GOT could constitute a system in ripening tomato fruit whereby the accumulation of inhibitory concentrations of oxaloacetate affecting the oxidation of succinate and malate might be controlled.     

Intracellular distribution of the steroidal glycoalkaloid α-tomatine in Lycopersicon esculentum fruit

Pericarp tissue from green tomato fruits was homogenized and separated into organelle fractions by differential centrifugation. Tomatine was found mainly in the final (105 000g) supernatant, with small amounts in the microsomes. Expressed sap from intact tissue was also rich in the alkaloid. It is suggested that tomatine accumulates in the vacuoles and/or soluble phase of the cytoplasm and is possibly synthesized in microsomal organelles.     

Biosynthesis and distribution of tomatine in cultured excised Lycopersicon esculentum roots

Growth of cultured excised tomato roots in the presence of ¹⁴C-mevalonic acid lactone results in labelling of tomatine. In the main axis of the root, incorporation was greatest in the apical meristematic region. Tomatine was present in equal concentrations in all parts of the cultured root system.     

Regulatory properties of a partially purified preparation of pyruvate kinase from Fasciola hepatica

It possesses sigmoid kinetics with PEP; FBP activation changes the relationship to a rectangular hyperbola. The enzyme is inhibited by malate, which competes with PEP; FBP relieves the inhibition slightly. ATP and bicarbonate ions are also inhibitory at high concentrations. ATP inhibition is mixed-competitive with PEP; bicarbonate inhibition is non-competitive. It is suggested that pyruvate kinase may regulate both lactate and acetate production by moderating the size of the cytosolic pyruvate pool.     

Identité des formes soluble et solubilisée à partir des mitochondries de l'alanine α-cetoglutarate aminotransferase de Lycopersicon esculentum

Alanine 2-oxoglutarate aminotransferase, extracted by Triton X-100 from tomato mitochondria, has been purified and its main kinetic characteristics determined. This form is more unstable than the soluble enzyme. However, the chromatographic patterns, effect of pH on stability, the pH optimum, the specificity and the apparent molecular weight show that it is the same enzyme and not an isoenzyme. This identity is confirmed by the results of kinetic studies and by the inhibition data by the products of the reaction for the two forms. The kinetic results also show that the two forms reversibly catalyze the transamination reaction between alanine and 2-oxoglutarate according the Ping Pong mechanism described for the soluble enzyme.     

L'alcool deshydrogénase de tomate (Lycopersicon esculentum): Étude cinétique et mécanisme d'action

In order to investigate the enzymatic mechanism of tomato alcohol dehydrogenase, kinetic studies were carried out at pH 5.8 and 9.4 for the forward and reverse reactions, respectively. Primary double reciprocal plots for several fixed concentrations of the associated substrate in all cases intersect, suggesting a sequential mechanism. Exploitation of secondary plots (slope-intercept values on the primary plots versus the reciprocals of the non-varied substrates) gives the following values: K_ms 500 μM for MeCHO, 30 μM for NADH, 2700 μM for EtOH, 12 μM for NAD⁺; K_is 40 μM for MeCHO, 3 μM for NADH, 10⁴ μM for EtOH and 45 μM for NAD⁺. The results obtained in product inhibition studies agree with an ordered bi-bi mechanism for both forward and reverse reactions. Application of Cleland's rules shows that the coenzyme was the first substrate to complex with the enzyme in both cases.     

Potassium requirement of pyruvate kinase extracted from leaves of halophytes

Pyruvate kinase enzymes were partially purified from leaves of halophytes, Atriplex gmelini C. A. Mey., Chenopodium acuminatum Wild, and Spergularia salina J. et C. Presl., grown hydroponically in the presence of 250 m M NaCl in a greenhouse, to determine their K_m values for potassium. The values were all ca 10⁻³ M , as also reported for the glycophyte enzymes. However, the K_m values were reduced by 60 to 70% by the addition of betaine to a concentration of 1 M .     

Cloning, Expression, and Mapping of GDP-D-mannose Pyrophosphorylase cDNA from Tomato (Lycopersicon esculentum)

GDP-D-mannose pyrophosphorylase (GMP, EC 2.7.7.22) catalyzes the synthesis of GDP-D-mannose and represents the first committed step in plant ascorbic acid biosynthesis. Using potato GMP cDNA sequence as a querying probe, 65 highly homologous tomato ESTs were obtained from dbEST of GenBank and the putative cDNA sequence of tomato GMP was assembled. The full-length GMP cDNA of tomato was cloned by RACE-PCR with primers designed according to the assembled cDNA sequence. The full-length cDNA sequence contained a complete open reading frame (ORF) of 1 086 bp, which encoded 361 amino acid residues. This gene was designated as LeGMP (GenBank accession No. AY605668). Homology analysis of LeGMP showed a 96% identity with potato GMP and the deduced amino acid showed 99%, 97%, 91% and 89% homology with GMP from potato, tobacco, alfalfa and Arabidopsis thaliana, respectively. Northern blot analysis showed that LeGMP was constitutively expressed in roots, stems, leaves, flowers and fruits of tomato; but the expression levels varied.LeGMP was mapped to 3-D using 75 tomato introgression lines (ILs), each containing a single homozygous RFLP-defined chromosome segment from the green-fruited species Lycopersicon pennellii.     

Effect of phenolic compounds in Lycopersicon esculeutum on the synthesis of ethylene

Caffeic, coumaric, sinapic and ferulic acids and naringenin were found in green tomato fruit, Chlorogenic acid accounted for 75% of the total phenolics in mature green fruit but only 35% in ripe fruit. There was very little change in the phenolic composition of the flesh of the fruit during ripening, whereas in the skin, naringenin increased markedly at the onset of the climacteric and three unidentified compounds increased during the climacteric rise. The increase in the concentration of naringenin was accompanied by an increase in the production of ethylene in the skin. Investigation of three systems producing ethylene from 4-methylmercapto-2-oxobutyric acid in the presence of peroxidase, showed that only p`-coumaric acid or naringenin were capable of acting as phenolic substrates, the other phenolic compounds being inhibitory.     

Interactions of temperature and pH on the regulatory properties of pyruvate kinase from organs of a marine mollusc

The effects of low temperature assay (5 °C) on the properties of the aerobic (low phosphate) vs. anoxic (high phosphate) forms of pyruvate kinase (PK) from foot muscle and gill of the whelk Busycon canaliculatum (L.) were assessed at two pH values, pH 7.00 and 7.25, and compared to control conditions of 20 °C and pH 7.00 (all assayed in imidazole buffer). When pH was held constant at 7.00, the decrease in assay temperature to 5 °C had large effects on the measured kinetic parameters of all PK forms, as compared to 20 °C and pH 7.00. However, when assay pH was allowed to rise, from 7.00 to 7.25, with the temperature decrease to 5 °C there were fewer alterations of kinetic parameters and quantitatively smaller changes to enzyme properties. It appears, then, that when pH rises with decreasing temperature following alphastat predictions, kinetic properties of PK are largely conserved. Low temperature, at either pH value, had several significant effects on PK properties. For example, low temperature raised the S_0.5 for phosphoenolpyruvate of PK-anoxic from gill by 3–6 fold and decreased the I₅₀ Mg · ATP for PK-anoxic from foot by the same amount. Arrhenius plots of PK activity for the gill PK forms showed a distinct break at 10 °C; > 10 °C Q₁₀ was 2.5 whereas < 10 °C Q₁₀ was 8.4. Temperature-dependent changes in all cases affected enzyme properties in a manner that would restrict enzyme function at low temperature.     

Molecular characterization of plastid pyruvate kinase from castor and tobacco

Clones encoding two different forms of plastid pyruvate kinase (PK_p; EC 2.7.1.40) have been isolated from both castor and tobacco seed cDNA libraries. One form, designated PK_pA, from castor was described in a previous report, and the tobacco homologue of PK_pA has now been isolated. In addition, a second cDNA, designated PK_pG, has been identified and sequenced in both species. Western blot analysis, using antibodies raised against protein overexpressed from these clones, indicates that they encode the two predominant polypeptides of plastid pyruvate kinase from developing castor endosperm. In castor, both PK_pA and PK_pG are encoded by single genes. In the allotetraploid Nicotiana tabacum, there are two copies of each, one derived from each of the progenitors of this species. The expression of the genes for PK_pA and PK_pG was examined in various tissues from both castor and tobacco. In castor, both forms are expressed in developing and germinating endosperm and in the root but neither is expressed in the leaf. In tobacco, both forms are expressed in developing seeds but in mature tissues, PK_pA is most abundant in roots and PK_pG in leaves.     

Distribution in excised Lycopersicum esculentum roots of the principal enzymes involved in sucrose metabolism

Sucrose synthetase and sucrose phosphate synthetase could not be detected in 7-day-old excised tomato roots grown in sucrose. These roots, however, possessed a highly active acid invertase and a neutral invertase of low activity. The distribution of the cell wall-located acid invertase along the root axis appeared to be related to growth. This was not the case for the soluble enzyme. The possible functions of these two enzymes are discussed.