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  • 1
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Sixty-seven hydroxyproline-resistant (hypr) cell lines were selected from cell suspensions of a diploid potato (Solanum tuberosum L., clone H2578) after plating on 5 and 10 mM hydroxyproline (hyp). Resistant colonies were obtained with a spontaneous frequency of 2.9×10−6. No clear influence could be shown from treatment with N-ethyl-N-nitrosourea (10 or 50 μM). Ninety % of the variant lines contained more proline than the wild type when cells were grown away from hyp for 1 month. Total free amino acid content was increased 2.2 to 6.8 times. When the lines were grown for another 2–5 months on non-selective medium, the content of proline and other amino acids and hyp resistance decreased. After this period the values were, however, still substantially higher than in the wild type. When tested for growth on media with other amino acid analogues (azetidine-2-carboxylic acid and dehydroproline, analogues of proline; aminoethyl-cysteine, analogue of lysine and 3-fluorotyrosine, analogue of tyrosine) and on media with inhibitory concentrations of lysine + threonine. lines H4a and H4b4 were cross resistant to these compounds. When tested on media with inhibitory NaCl concentrations, variant lines H2a, H4a, and H6 showed better tolerance than the wild type. One variant cell line (H4a) was successfully regenerated into plants. Preliminary results showed an increased frost tolerance in the leaves of these plants (−4.5°C compared to −3°C for the wild type), accompanied by a higher leaf proline content. Callus initiated from leaves of the regenerated clones was more resistant to hyp than wild type callus, indicating that the variant trait might be due to a mutation.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 66 (1986), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The accumulation of labelled ions was measured in seedlings of Arabidopsis thaliana (L.) Heynh. grown in submerged cultures. Genotypes used were wild type and the nitrate-uptake mutant B1, which is altered in the uptake of nitrate and chlorate from concentrations above 1 mM when grown under normal conditions. At low and high concentrations of chlorate, chloride, and K+, significantly less radioactivity was accumulated in seedlings of B1 than in seedlings of wild type. The influx of sulphate did not decrease in B1. The results indicate that the effect of the mutation in B1 is restricted to the uptake of monovalent ions.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 64 (1985), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Frost tolerance and leaf proline content were examined in a number of potato hybrids selected for frost tolerance and in the cv. Astarte before and after hardening. Cold hardening (2°C for 20 days) in a dry environment (50/90% relative humidity, day/night) resulted in decreased water content, increased proline content and increased frost tolerance of the leaves of all genotypes. Frost tolerance before and after hardening was positively related to leaf proline content, but not to leaf water content. Drought stress alone, imposed by wilting excised leaves for 4 days, resulted in an accumulation of proline comparable to that after hardening in a dry environment, but the increase in frost tolerance was smaller. Cold hardening in a humid environment (90% relative humidity continuously) only caused a minor accumulation of proline and a small increase in frost tolerance, but the increase in frost tolerance was high in relation to the amount of proline accumulated. Proline, exogenously applied to one of the genotypes, was accumulated in the leaves of shoot cultures, resulting in an increase in frost tolerance. A possible role of proline in frost tolerance is discussed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 54 (1982), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A chlorate-resistant mutant B25 of Arabidopsis thaliana (L.) Heinh. was isolated, which has very little or no in vitro nitrate reductase activity and grows poorly on a substrate with nitrate as the sole nitrogen source. The mutation of B25 (rgn) is monogenic and recessive, tightly linked to the marker gene an on chromosome 1. Nitrate induces cytochrome-c reductase activity in the mutant but to a lower level than in the wildtype. After sucrose gradient centrifugation the greatest part of the cytochrome-c reductase from induced wildtype is found as 8s type whereas cytochrome-c reductase from B25 under the same conditions is found as 4s type. Nitrate reductase is found at the 8s position. It is suggested that B25 has lost the ability to assemble two 4s subunits showing cytochrome-c reductase activity and a Mo-bearing co-factor into the functional nitrate reductase. Nitrate rather than nitrite is the inducing agent for nitrite reductase, since in B25 nitrite reductase is even more rapidly induced than in the wildtype after addition of nitrate. Both the wildtype and B25 contain a nitrate reductase inhibiting factor when grown on ammonium. This inhibiting factor is a small protein, possibly similar to the nitrate reductase inactivating enzyme reported for other plants.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 43 (1978), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A study of nitrate and chlorate uptake by Arabidopsis thaliana was made with a wildtype and two mutant types, both mutants having been selected by resistance to high chlorate concentrations. All plants were grown on a nutrient solution with nitrate and/or ammonium as the nitrogen source. Uptake was determined from depletion in the ambient solution. Nitrate and chlorate were able to induce their own uptake mechanisms. Plants grown on ammonium nitrate showed a higher subsequent uptake rate of nitrate and chlorate than plants grown on ammonium alone.Mutant B25, which has no nitrate reductase activity, showed higher rates of nitrate and chlorate uptake than the wildtype, when both types were grown on ammonium nitrate. Therefore, the uptake of nitrate is not dependent on the presence of nitrate reductase. Nitrate has a stimulating effect on nitrate and chlorate uptake, whereas some product of nitrate and ammonium assimilation inhibits uptake of both ions by negative feedback. Mutant B 1, which was supposed to have a low chlorate uptake rate, also has disturbed uptake characteristics for nitrate.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-5028
    Keywords: Agrobacterium tumefaciens ; adventitious shoot regeneration ; transformation ; homozygous potato
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transformed potato (Solanum tuberosum) plants were obtained from homozygous diploid potato by using a transformation procedure in combination with an adventitious shoot regeneration method. Leaf and stem explants were inoculated with an Agrobacterium tumefaciens strain which contained a binary vector (pVU 1011) carrying the neomycin phosphotransferase gene. Shoot regeneration most effectively on stem explants, occurred within six weeks directly from the explants without introducing a callus phase. A strong seasonal influence on transformation efficiencies was observed. Analysis of a number of randomly selected regenerated shoots for their ability to root and form shoots on kanamycin-containing medium shows that over 90% of the regenerated shoots obtained are transformed. In a number of shoots transformation was confirmed by a test for the presence and expression of the NPT-II gene.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-2242
    Keywords: Arabidopsis thaliana ; Chlorate resistance ; Nitrate reductase deficiency ; Suspension cultures ; M2-seeds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cell suspensions of diploid Arabidopsis thaliana were screened for resistance to chlorate on a medium with ammonium nitrate as the nitrogen source, and after plating on filters to increase the plating efficiency. Thirty-nine lines were selected, four of which were still resistant after two years of subculturing on non-selective medium. Of the latter lines three were nitrate reductase deficient but exhibited some residual nitrate reductase activity; the fourth line showed a high level of enzyme activity. Screening M2-seeds for callus production on selective medium with amino acids as the nitrogen source and chlorate revealed resistant calli in 17 out of 483 M2-groups. Nine well-growing lines, all but one (G3) exhibiting no detectable in vivo nitrate reductase activity, were classified as defective in the cofactor. Two lines (G1 and G3) could be analysed genetically at the plant level. Chlorate resistance was monogenic and recessive. Sucrose gradient fractionation of callus extracts of G1 revealed that a complete enzyme molecule can be assembled. Nitrate reductase activity in G1 could partly be restored by excess molybdenum. It is suggested that G1 is disturbed in the catalytic properties of the cofactor. It appeared that G1 is neither allelic with another molybdenum repairable mutant (B73) nor with another cofactor mutant (B25). Wilting of intact G1 plants could be ascribed to non-closing stomata.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-2242
    Keywords: Amino acid analogue-resistance ; Electrofusion ; Potato ; Solanum tuberosum L. ; Somatic hybridization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Intraspecific somatic hybridization between amino acid analogue-resistant cell lines of potato (Solanum tuberosum L.) has been carried out following electrofusion of protoplasts. In initial analytical electrofusion experiments (1 mm electrode separation) optimal fusion conditions were determined by changing the fusion medium (addition of Ca and/or spermine) and the electrical parameters. Subsequently, in large scale experiments, cell suspension protoplasts of aec-1, a variant resistant to AEC, were fused with the same type of protoplasts of 5mt-26 or 5mt-27, both variants resistant to 5MT and cross-resistant to 3 FT. After an extensive selection procedure only somatic hybrid lines of aec-1 + 5mt-26 were obtained. The resistance traits of aec-1 and 5mt-26 were expressed fully, indicating that the variant characters involved are transmitted dominantly. Quantitative examination of the free amino acid content revealed characteristics of both the parental cell lines in most of the somatic hybrids. However, initially selected double resistant colonies from fusions of aec-1 + 5mt-27 lines appeared not to be somatic hybrids.
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  • 9
    ISSN: 1432-2242
    Keywords: Agrobacterium rhizogenes ; Solanum tuberosum ; Binary vector ; Neomycin phosphotransferase ; β-Glucuronidase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Transgenic shoots were regenerated from eight diploid potato hairy root clones obtained by transformation with Agrobacterium rhizogenes harboring next to its wild-type Ri-plasmid a binary vector containing the neomycin phosphotransferase and the β-glucuronidase genes. The plants exhibited the typical hairy root phenotype. Of the plants isolated, 58% were tetraploid and 38% were diploid. Flowering and tuberization was much better in the diploid than in the tetraploid plants. Transgenic plants formed a significantly larger root system when grown on kanamycin-containing medium as compared to growth on kanamycin-free medium. Direct evidence for genetic transformation was obtained by opine, neomycin phosphotransferase and β-glucuronidase assays, and by molecular hybridization. Fourteen flowering diploid plants were reciprocally crossed with untransformed S. tuberosum plants, but only six were successful. Seedlings obtained from four crosses showed that all traits were transmitted to the offspring. Molecular analysis confirmed the presence of multiple integrations (copies) of both vector T-DNA and Ri-T-DNA. The genetic data, furthermore, suggest that the traits derived from Ri-T-DNA and binary vector T-DNA are linked, as no recombination between the different traits was observed.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-2242
    Keywords: Solanum tuberosum ; Mutant ; Starch composition ; Granule-bound starch synthase ; amylose-free
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An amylose-free potato mutant was isolated after screening 12,000 minitubers. These minitubers had been induced on stem segments of adventitious shoots, which had been regenerated on leaf explants of a monoploid potato clone after Röntgen-irradiation. The mutant character is also expressed in subterranean tubers and in microspores. Starch granules from the mutant showed a strongly reduced activity of the granule bound starch synthase and loss of the major 60 kd protein from the starch granules.
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