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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Planta 110 (1973), S. 303-310 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary ABA has been identified by GLC-MS and routinely determined by GLC as one of several inhibitory substances in the testa and pericarp of hazel nuts. Its concentration in newly harvested nuts, which had not developed embryo dormancy, was 19.0 nmoles/g dry weight for the testa, 1.4 nmoles/g for the pericarp and 0.09 nmoles/g for the embryo. Dry storage of the nuts resulted in the development of embryo dormancy together with a slight loss of ABA. On imbibition of dormant nuts at 5° C and 20° C there was a 61% loss of ABA from the testa and pericarp in both cases. However the 5° C imbibition resulted in the breaking of seed dormancy while the 20° C imbibition had no effect on the dormancy. The ABA of the testa and pericarp seems to be concerned with the maintenance of seed dormancy prior to the onset of embryo dormancy. Subsequent to the onset of embryo dormancy, ABA seems to show little effect on either the maintenance or breaking of seed dormancy.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Analogies and differences between the growth-promoting action of fusicoccin (FC), the toxic agent produced by Fusicoccum amygdali, and of indole-3-acetic acid (IAA) in etiolated pea internode segments were further investigated. It was confirmed that the effect of FC, at optimal concentration, on growth by cell enlargement is markedly higher (ca. 70%) than that of IAA. The lack of an inhibitory effect of FC at high concentrations corresponds to a lack of capacity of the toxin to induce ethylene synthesis. When FC and IAA are present together at suboptimal concentrations, the effects of the two substances are clearly additive. Growth stimulation by a mixture of FC and IAA at optimal concentrations is equal to that by FC alone. NaF, 2,4-DNP, actinomycin D, and cycloheximide strongly depress FC-induced stimulation of cell enlargement. These data are in agreement with the hypothesis that FC promotes growth through some effect on cell-wall extensibility probably identical to the one mediating auxin-induced growth, while the primary site of action of FC is different from that of the natural and synthetic auxins.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Planta 110 (1973), S. 345-351 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary There are two phases of 2-[14C]ABA uptake in lettuce fruits. Although the first phase appears to relate to the imbibition of water, uptake continues for three hours following complete imbibition. The second phase corresponds with the commencement of radicle extension. Exogenously applied radioactive ABA is metabolised to form an unidentified substance which has chromatographic properties different to previously described ABA metabolites. When ABA is present in the bathing solution, the quantity of metabolite never significantly exceeds that of labelled ABA in the tissues.
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  • 4
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1) In cotyledons of dry seeds from watermelons, 10 weak bands of MDH were detectable by electrophoresis (Fig. 1). After 3 hrs of germination, this pattern was reduced to 4 stronger bands whereas the total MDH activity remained unchanged. Artifacts were excluded by use of the reverse enzyme reaction (Fig. 2), different homogenizing media and mixing experiments. 2) Molecular weight comparisons (Fig. 3) showed that with the exception of a glyoxysomal band (exclusion b Sephadex G-200) appearing at day 2 all bands and subbands had the same values (somewhat below 60000). 3) Homogenization of cotyledons from dry seeds with 10 mM β-mercaptoethanol resulted in a 4 band pattern (Fig. 8) identical to that found 3 hrs after sowing. Treatment of older cotyledons did not influence the later pattern. Electrophoresis of the raw extracts in presence of NAD or/and malate did not change the number of bands, only the RF-values. Dialysis of raw extracts was without influence. 4) On the basis of these experiments it is concluded that during germination splitting processes of disulfide bridges take place which may result in conformation changes. According to this hypothesis dry seeds would contain 4 groups of conformational isoenzymes.
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  • 5
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The difference in activity of enzymes which are involved in the biosynthesis of flavonols (phenylalanineammonium-lyase, chalcone-flavanone isomerase) and of an enzyme which converts flavonols is studied during the development of anthers in Tulipa cv. Apeldoorn. The results are considered in relation to the accumulation of simple phenylpropanes, of an intermediate a chalcone and of different flavonoid compounds. In the stages of development with high activities of flavonol synthesizing enzymes there are also high activities in the flavonol converting enzymes. In these stages a large amount of derivates of p-coumaric acid and ferulic acid is accumulated as well as the intermediate product 2′,3,4,4′,6′-pentahydroxychalcone; accordingly only traces of flavonols can be found. An intensive accumulation of different flavonols does not start before the late phase of development of the anthers in which the stationary concentration of chalcones decreases. It is the stage when the activity of the flavonol converting enzyme decreases rapidly. The relations between the stationary concentration of flavonoid compounds and the interlacing of synthesis and turnover are discussed.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The growth of Thelypteris normalis (C. Chr.) Moxley gametophytes is inhibited under T. normalis sporophytes. Competition for minerals, light, change in pH, or microbial inhibitors were experimentally eliminated as causes of the inhibition. This is the first demonstration of allelopathy between a sporophyte and gametophyte in a fern. Two inhibitors, thelypterin A and B, which were released from the roots of the Thelypteris sporophyte, were isolated and a bioassay for the inhibitors was devised. Thelypterin A gave an Ehrlich-positive reaction indicative of secondary aromatic amines and an ultraviolet absorption spectrum indicative of a heterocyclic ring. The inhibitors affected the growth of Thelypteris, Pteris and Phlebodium gametophytes.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Planta 111 (1973), S. 13-22 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The rate of Na+/Na+ exchange as measured with 24Na+ in Na+-rich cells of Chlorella pyrenoidosa is governed by a single rate constant and saturates with increasing external Na+ concentration. The K mvalue for this process is 0.8 mM Na+ and the maximum rate of exchange in illuminated cells is about 5 pmoles cm-2 sec-1. These values contrast with a K mof 0.18 mM K+ and maximum rate of about 17 pmoles K+·cm-2·sec-1 for net K+ influx. Although the Na+/Na+ exchange was only slightly sensitive to light it was inhibited by the uncouplers CCCP and DNP and by the energy transfer inhibitor DCCD. This inhibition of the rate of Na+/Na+ exchange was not accompanied by a loss of internal Na+. Both the effect of external K+ on 24Na+ influx into Na+-rich cells and the inhibition of net K+ uptake by the presence of external Na+ indicates that Na+/Na+ and K+/Na+ exchanges share the same carrier and that the external site of this carrier has a three to four times higher affinity for K+ over Na+.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Planta 111 (1973), S. 41-46 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The influence of nitrite and nitrate on chlorophyll fluorescence, a very sensitive indicator for the redox state of the primary acceptor of photosystem II of photosynthesis, was studied in green algae (several species of Chlorella, and Ankistrodesmus braunii). In phosphate solution under an atmosphere of nitrogen (i.e., in the absence of O2 and CO2, and without nitrite or nitrate), fluorescence shows a pronounced induction and then rises to a high steady-state level. In the presence of nitrite, however, fluorescence decreases after a rather short induction peak to a much lower steady-state. Nitrate, on the other hand, does not have any influence on either induction or steady-state of fluorescence. These results clearly demonstrate that nitrite reduction in the light is very closely coupled to the photosynthetic electron transport system, whereas nitrate is not reduced photosynthetically in vivo.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Planta 111 (1973), S. 47-56 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nitrite reductase from barley seedlings was purified 50–60 fold by ammonium sulphate precipitation and gel filtration. No differences were established in the characteristics of nitrite reductases isolated in this way from either leaf or root tissues. The root enzyme accepted electrons from reduced methyl viologen, ferredoxin, or an unidentified endogenous cofactor. Enzyme activity in both tissues was markedly increased by growth on nitrate. This activity was not associated with sulphite reductase activity. Microbial contamination could not account for the presence of nitrite reductase activity in roots. Nitrite reductase assayed in vitro with reduced methyl viologen as the electron donor was inhibited by 2,4-dinitrophenol but not by arsenate.
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  • 10
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cell-free extracts from seeds of Juglans regia synthesize tryptophan from L-serine and indole. Tryptophan synthetase has maximal activity in the range between pH 7 and 8. The enzyme is associated with a particulate fraction (density 1,210 g/ml) which is separated from the mitochondria (density 1,191 g/ml) after isopycnic density centrifugation on a continuous sucrose gradient.
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