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  • 1
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: By using suitable unsymmetrical derivatives of terephthalic acid and ethylene glycol we synthesized linear oligoesters from poly-ethylene-glycol-terephthalate-type. Thus we obtained the first five representatives of the diols and the first three representatives of the hydroxycarboxylic acids with terminal benzyl groups. From hydrogenolysis under atmospheric pressure at 70-90°C. the corresponding diols and hydroxycarboxylic acids have obtained. The cleavage of the benzyl-ether and -ester groups with anhydrous aluminumchloride yielded no pure products.We were not successfull so far in synthesizing cyclic oligoesters.The relation between viscosity and molecular weight in the series of the dibenzyldiols could be represented by the expression \documentclass{article}\pagestyle{empty}\begin{document}$ [\rm{\eta ] = K} \cdot \rm{M}^\rm{\alpha } \rm{ with K = 0}\rm{.0077 [ml} \cdot \rm{/g} \cdot \rm{] and \alpha = 0}\rm{.95} $\end{document}.By W-analysis we found that the molar extinction coefficient a t 242.5 my is proportional to the number of terephthalic acid units in the molecule. The concentration of terminal benzyl groups is related to the value of \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{\rm{\varepsilon 215.5 m\mu }}} {{\rm{\varepsilon 242.5 m\mu }}} $\end{document}.The oligoesters have been examined by IR- and X-ray methods.
    Notes: Mit Hilfe geeigneter monofunktioneller Derivate von Terephthalsäure und Glykol gelang der schrittweise Aufbau von Oligoglykolterephthalaten. Die benzylgeschützten Diole wurden bis zum Pentameren, die geschützten Hydroxycarbonsäuren bis zum Trimeren synthetisiert. Durch Hydrogenolyse der benzylgeschützten Verbindungen bei 70-90°C unter Normaldruck wurden die freien Diole bis zum Pentameren und die Hydroxycarbonsären bis zum Trimeren gewonnen. Von den zur Entfernung der Benzylschutzgruppen erprobten übrigen Methoden lieferte bisher nur diejenige mit wasserfreiem Aluminiumchlorid einen Teilerfolg.Erste orientierende Versuche zur Synthese von Cyclo-tris-glykolterephthalat blieben erfolglos.Viskosimetrische Messungen an den synthetisierten Oligoestern zeigten, daß für die Reihe der Dibenzyldiole vom Dimeren an ein Gesetz \documentclass{article}\pagestyle{empty}\begin{document}$$ [{\rm \eta ] = K} \cdot {\rm M}^{\rm \alpha}\ \hbox {mit K = 0,0077 [ml/g] und}\ \alpha = 0,95 $$\end{document} gilt.Der molare Extinktionskoeffizient bei 242,5 mμ ist der Anzahl der Terephthalsäureeinheiten linear proportional. In der Reihe der benzylgeschützten Oligoester ist der \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{\rm{\varepsilon 215,5 m\mu }}} {{\rm{\varepsilon 242,5 m\mu }}} $\end{document}-Wert ein Maß für die Endgruppenkonzentration.Alle Verbindungen wurden infrarotspektroskopisch und röntgenographisch untersucht.
    Additional Material: 2 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Planta 166 (1985), S. 141-144 
    ISSN: 1432-2048
    Keywords: Amino acid uptake ; Leaf (amino acid uptake) ; Mutant (valine-resistant) ; Nicotiana (amino acid transport) ; Transport (membrane) ; Valine resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The uptake rates of 16 amino acids were measured in leaf discs from Nicotiana tabacum L., cv. Xanthi (wild type) and from two valine-resistant mutants, Valr-1 and Valr-2. For all amino acids tested the uptake rates in Valr-1 were similar to those in the wild type. The Valr-2 mutant showed a reduced uptake of neutral and acidic amino acids, but uptake of the basic amino acids was only slightly lower than in the wild type. It is argued that two systems for amino-acid transport are present: one for neutral and acidic amino acids and the other for basic amino acids.
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  • 3
    ISSN: 1432-2048
    Keywords: Lactuca (nitrate accumulation) ; Malate utake ; Nitrate uptake ; Vacuole (nitrate, malate uptake)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Vacuoles were isolated from leaves of two lettuce (Lactuca sativa L.) genotypes that differed significantly in their nitrate accumulation. The rate of nitrate uptake into the vacuoles did not differ between the genotypes, but the malate-uptake rate did. Fitting a Michaelis-Menten equation, with or without the addition of a linear term, showed that the rates of malate and nitrate uptake can be best described by saturation kinetics for both genotypes. Malate transport across the tonoplast showed a Km value of approx. 40 mM, while the Km value for nitrate uptake was approx. 5 mM. Both malate and nitrate uptake were greatly stimulated by ATP, but not by pyrophosphate. Valinomycin considerably blocked both malate and nitrate uptake while nigericin only slightly affected the rate of malate uptake and had no effect on the nitrate-uptake rate. This indicates that both nitrate and malate transport are driven by the membrane potential, while the pH gradient may play a minor role in malate transport only. The presence of nitrate in the incubation medium inhibited malate uptake (2 mM nitrate caused an inhibition of approx. 50%). In contrast to this, the presence of malate in the incubation medium did not inhibit nitrate uptake. Endogenous nitrate did not affect malate uptake. Thus, we did not find genotypic differences in the uptake pattern which could explain the variation in nitrate accumulation. The possible reason for differences in nitrate accumulation in vivo is discussed.
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  • 4
    ISSN: 1432-2048
    Keywords: Amino acid efflux ; Membrane transport ; Phloem unloading ; Pisum (seed coats) ; Seed development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Using the empty-seed-coat technique, we have studied the release of amino acids from pea (Pisum sativum L. cv. Marzia) seed coats, either attached to or detached from the mother plant, at various stages of development. During an experimental period of 8 h, about 70% of the amino-acid content of the seed coat was released into the solution with which the seed-coat cup was filled. Major components of the released amino-acid mixture were glutamine (25%), alanine (20%) and threonine (15%). At the end of the experimental period (t≥6 h) the amino-acid efflux from attached seed coats was approx. 0.15 μmol · h−1·(seed coat)−1 greater than that from detached seed coats. This difference may be attributed to the import of amino acids into attached seed coats. It is equivalent to approx. 0.3 μmol N · h−1 · (seed coat)−1, whereas the nitrogen demand of the embryo amounted to 0.50 ± 0.04 μmol N · h−1 · embryo−1. The time course of the release from detached seed coats could be described by the sum of two exponentials with t1/2 = 0.4–0.7 h and t1/2 = 3.3–6.9 h, respectively, which probably represent the emptying of the cytoplasmic and vacuolar compartments. During development the vacuolar amino-acid pool decreased considerably (from 6.2 to 1.4 μmol · (seed coat)−1), whereas the cytoplasmic pool was much more constant (2.1–1.2 μmol · (seed coat)−1). For attached seed coats it will be shown that the time course of the amino-acid release could be fully accounted for by the sum of two exponentials and a linear term, where the parameters of the exponentials were, within error, the same as for detached seed coats and the linear term represented the import of amino acids. The results will be discussed with reference to prevailing models of phloem unloading in the seed coat, and in relation to the flux of amino acids from seed coat to the developing embryo.
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  • 5
    ISSN: 1432-2048
    Keywords: Arabidopsis ; Amino acid transport systems ; Gene mapping ; Proline (uptake kinetics)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The raz1 mutant of Arabidopsis thaliana (L.) Heynh. has been selected as resistant to the toxic proline analogue, azetidine-2-carboxylic acid (2AZ). Seedlings of the mutant tolerated fivefold higher concentrations of 2AZ (ED50 = 0.25 mM) than the wild-type seedlings (ED50 = 0.05 mM). The mutant gene was found to be semi-dominant and the corresponding RAZ1 locus was mapped on chromosome 5 at 69.6±1.8 cM. The resistance to 2AZ could be fully and exclusively accounted for by the lower uptake rate of the proline analogue in the mutant. The influx of L-proline in roots of wild-type seedlings could be dissected into two components: (i) a component with a high affinity and a low capacity for l-proline (K m≈20 gmM, V max≈60 nmol·(g FW)-1·h-1) and also a high affinity for L-2AZ (K i≈40 μM) and (ii) a low-affinity, high-capacity component (K m≈5 mM: V max = 1300 nmol·(g FW)-1·h-1). Clearly, the raz1 mutation affects the activity of a high-affinity transporter, because the high-affinity uptake of proline in the mutant was at least fivefold lower than in the wild-type, whereas the low-affinity uptake was unchanged.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Planta 151 (1981), S. 314-319 
    ISSN: 1432-2048
    Keywords: Amino acids, branch chained ; Spirodela
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The joint action of L-valine and L-isoleucine, L-leucine and L-isoleucine, and L-valine and L-leucine on the growth of Spirodela polyrhiza was established. The effect of one branched-chain amino acid on growth inhibition by another one was compared with the non-specific antagonisms which glycine and L-alanine exert on growth inhibition by singly supplied branched-chain amino acids. In this way specific and non-specific interactions could be distinguished. It appeared that: (1) L-isoleucine was a specific antagonist of L-valine; (2) L-leucine was a specific antagonist of L-isoleucine; (3) L-valine and L-leucine were synergistic growth inhibitors. Further, it was found that: (4) growth inhibition by L-leucine was specifically antagonized by simultaneously supplied L-valine and L-isoleucine; (5) an excess of L-isoleucine strongly inhibited the conversion of exogenous valine into leucine; (6) accumulation of valine was typical of isoleucine-induced growth inhibition. The results are consistent with the view that growth inhibition by L-valine and L-leucine is due to the blocking of acetohydroxy acid synthetase, the first common enzyme in the valine-isoleucine biosynthetic pathway. Growth inhibition by L-isoleucine, however, seems to result from inhibition of leucine synthesis at a step after 2-oxoisovaleric acid. Some aspects of the regulation of branched-chain amino acid biosynthesis in higher plants are discussed.
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  • 7
    ISSN: 1432-2048
    Keywords: Glucose ; Membrane transport ; Phloem unloading ; Pisum (seed coat, sugar) ; Sucrose ; Uptake (kinetics, sugar)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Uptake of 14C-labelled sucrose and glucose by isolated seed coat halves of pea (Pisum sativum L. cv. Marzia) seeds was measured in the concentration range 〈0.1 μM to 100 mM. The initial influx of sucrose was strictly proportional to the external concentration, with a coefficient of proportionality (k) of 6.2 μmol·(g FW)−1·min−1·M−1. Sucrose influx was not affected by 10 μM carbonylcyanide m-chlorophenylhydrazone (CCCP), but it was inhibited by 40% in the presence of 2.5 mM p-chloromercuribenzenesulfonic acid (PCMBS). Influx with diffusional kinetics was also observed for glucose (k = 4.8 μmol·(g FW)−1·min −1·M −1) and mannitol (k = 5.1 μmol·(g FW)−1·min−1·M−1). For glucose an additional saturable system was found (Km = 0.26 mM, V max = 4.2 nmol·(g FW)−1·min−1), which appeared to be completely inhibited by CCCP and partly by PCMBS. In contrast to the diffusional pathway, uptake by this saturable system was slightly pH-dependent, with an optimum at pH 5.5. The influx of sucrose appears to be by the same pathway as the efflux of endogenous sucrose, which was inhibited by 36% in the presence of 2.5 mM PCMBS (De Jong A, Wolswinkel P, 1995, Physiol Plant 94: 78–86). It is argued that passive transport may be the only mechanism for sucrose transport through the plasma membrane of seed coat parenchyma cells. The estimated permeability coefficient of the plasma membrane for sucrose (P = 3.5·10−7 cm·s−1) is more than 1 × 106-fold higher than that reported for artificial lipid membranes. This relatively high permeability is hypothesized to result from pore-forming proteins that allow the diffusion of sucrose. Furthermore, it is shown that a sucrose gradient across the plasma membrane of the seed coat parenchyma of only 22 mM will suffice to result in the net efflux of sucrose which is required to feed the embryo.
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  • 8
    ISSN: 1432-2048
    Keywords: Amino acid biosynthesis ; Leucine ; Metabolic regulation ; Spirodela ; Valine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Duckweed colonies were grown on 1 l of nutrient solution supplied with 10 μM l-[14C]leucine or with 25 μM l-[14C]valine. Under these conditions the exogenously supplied amino acid did not inhibit growth, but caused in the plants a moderately increased pool of that amino acid, which remained essentially constant during the culture period. The effect of the increased pool of valine or leucine on the biosynthesis of these amino acids was determined from isotope dilution in the protein-bound valine and-or leucine. An increase in the leucine pool from 1.1 to 5.0 nmol mg−1 dry weight resulted in a 21% reduction of metabolite flow through the common part of the valine-leucine biosynthetic pathway; leucine synthesis was reduced by 35%, but valine synthesis by only 5% and isoleucine synthesis was apparently unaffected. An increase in the valine pool from 3.2 to 6.6 nmol mg−1 dry weight reduced the metabolite flow through the valine-leucine pathway by 48%, valine synthesis by 70%, and leucine synthesis from pyruvate by 29%, which was compensated by leucine synthesis from exogenous valine, whereas the synthesis of isoleucine was not changed. It is concluded that the biosynthesis of valine and leucine is mainly controlled by feedback inhibition of acetohydroxyacid synthetase. In vivo, the feedback inhibition can be exerted in such a way that synthesis of acetolactate (the precursor of valine and leucine) is appreciably reduced, whereas synthesis of acetohydroxybutyrate (the isoleucine precursor) is not inhibited.
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  • 9
    ISSN: 1432-2048
    Keywords: Amino acid uptake ; Membrane transport ; Mutant tobacco (valine-resistant) ; Nicotiana (mutant) ; Phloem loading ; L-Valine (uptake kinetics)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Uptake rates of L-valine in epidermis-free leaf discs of tobacco (Nicotiana tabacum L. cv. Xanthi) were measured over the concentration range 0.1 μM to 50 mM. Wild-type tobacco was compared with the digenic mutant Valr-2 (genotype vr2/vr2; vr3/vr3), and with the monogenic mutant strains h9 and h10 (genotype +/+; vr3/vr3) and h17 and h23 (genotype vr2/vr2; +/+). Rate equations consisting of one to three Michaelis-Menten terms, possibly in combination with a linear term were fitted to the kinetic data. These rate equations are equivalent to rational polynomials which may be regarded as the general type of mathematical function describing the kinetics of enzymes and carriers. Kinetic data of the four genotypes conformed to the sum of three Michaelis-Menten terms. Accordingly, three kinetic components could be distinguished. In the wild-type the approximate Kms were 40 μM, 1mM, and 40 mM, respectively. In Valr-2 a component with a very low Km (about 4 μM) was found which may represent either the modified low-Km component of the wild-type or a fourth component which is undetectable in the wild-type by kinetic analysis. The Vmax of the low-Km component in Valr-2 was at least a 100-fold lower than in the wild-type. In the presence of one of the mutant genes the calculated Vmax of the low-Km component was 48% (strains h9 and h10) or 40% (strains h17 and h23) of the corresponding Vmax in the wild-type. It is reasoned that the mutations have no effect on the activity of the other two kinetic components, though the evidence for this is circumstantial. Autoradiographs of leaf discs showed that in Valr-2 the uptake of 14C-labelled valine in both mesophyll and minor veins was strongly reduced as compared with the wild-type.
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  • 10
    ISSN: 1432-2048
    Keywords: Amino acid release ; Efflux (amino acid) ; Pisum (amino acid, cotyledon) ; Seed development ; Tonoplast ; Turgor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The release of endogenous amino acids from isolated, immature pea (Pisum sativum L. cv. Marzia) cotyledons was investigated in relation to their developmental stage and the osmolarity of the bathing medium. The water potential of the cotyledons was about-1.1 MPa from which it could be inferred that the osmolarity of their apoplastic fluids will be approximately 450 mosmol·l−1. The time course of amino-acid release conformed to an exponential function. Rate constants of the release were in the range 0.3 to 0.9 · h −1. No indication was found for increased permeability of the plasmamembrane for amino acids at low medium osmolarity. Rate constants were even 1.5-fold lower in 0 mM mannitol than in medium with 400 mM mannitol. This effect could be ascribed to reduced protein synthesis in hypotonic media. In the presence of 400 mM mannitol the release was nearly proportional to the total amino-acid pool of the cotyledons and ranged from 12% to 8% for the various developmental stages. Amino-acid release was stimulated by incubation in a hypotonic medium (〈 400 mM mannitol), up to fourfold in a medium without mannitol where as much as 45% of the cotyledonary amino-acid content could be released. The extra aminoacid release induced by the hypotonic condition declined during development and eventually vanished completely. Release of amino acids into a medium with 400 mM mannitol was more selective than into a medium without mannitol. For instance, arginine was one of the main constituents of the cotyledonary amino-acid pool (19%) as well as of the released amino-acid mixture when the medium contained no mannitol (10%), whereas it was virtually absent when the medium contained 400 mM mannitol. As an overall interpretation of these results, it is proposed that the hypotonic condition greatly enhances the permeability of the tonoplast (not that of the plasmalemma) for amino acids so that the otherwise well-sequestered amino acids in the vacuole become available for release into the bathing medium.
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