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  • 1
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Changes in carbon metabolism and δ13C value of transgenic potato plants with a maize pyruvate,orthophosphate dikinase (PPDK; EC 2.7.9.1) gene are reported. PPDK catalyzes the formation of phosphoenolpyruvate (PEP), the initial acceptor of CO2 in the C4 photosynthetic pathway. PPDK activities in the leases of transgenic potatoes were up to 5.4-fold higher than those of control potato plants (wild-type and treated control plants). In the transgenic potato plants, PPDK activity in leaves was negatively correlated with pyruvate content (r2= 0.81), and was positively correlated with malate content (r2= 0.88). A significant increase in the δ13C value was observed in the transgenic potato plants, suggesting a certain contribution of PEP carboxylase as the initial acceptor of atmospheric CO2. These data suggest that elevated PPDK activity may alter carbon metabolism and lead to a partial operation of C4-type carbon metabolism. However, since parameters associated with CO2 gas exchange were not affected, the altered carbon metabolism had only a small effect on the total photosynthetic characteristics of the transgenic plants.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The physiological and molecular events of ethylene-induced abscission in mature fruit calyx, laminar and floral abscission zones of cv. Valencia orange were examined. Continuous exposure of fruit explants to 5 µl 1−1 ethylene for 2 to 40 h resulted in marked increases in endo-1,4-β-glucanase (cellulase) and polygalacturonase (PG) activities in calyx abscission zones. Two abscission-related cellulases and one PG were found. The major peak of cellulase activity corresponded to a pI of 8.0 and molecular weight of 51 kDa, whereas the minor cellulase peak had a pI of 5.5. The abscission polygalacturonase had a pI of 5.5. Calyx abscission zone RNA was amplified with degenerate primers based on sequence of the purified Valencia orange calyx abscission cellulase, and cloned. The two partial cellulase cDNA clones were 59% identical at the nucleotide level. Genomic Southern analysis suggested that Valencia orange contained two groups of cellulase genes. A full-length cDNA clone from each group was isolated from a cDNA library prepared from ethylene-induced calyx abscission zone mRNA. Both genes were expressed in ethylene-induced calyx, laminar and floral abscission zones, but were not expressed in non-induced abscission zones or mature leaves treated with or without ethylene, young bark or young fruit of Valencia.
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 102 (1998), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The genetics and expression of pectinesterase (PE) genes were examined in Valencia orange. Degenerate primers based on partial amino acid sequence of a 36 kDa PE protein isolated from juice vesicles were used to amplify a 350 bp DNA fragment from cDNA prepared from juice vesicle total RNA. Two groups of 350 bp PE clones with 66% sequence identity were isolated. A clone from each group was used to screen a Valencia orange genomic DNA λ library. Two different lambda clones that contained complete PE coding sequence (CsPME1 and CsPME3) and a third lambda clone that contained partial PE sequence (CsPME2) were characterized. The CsPME1 gene contained two exons (1063 and 689 bp) interrupted by a 1452 bp intron, whereas the CsPME3 gene had two exons (844 and 686 bp) interrupted by a 771 bp intron. CsPME1 shared significant sequence similarity with the partial clone CsPME2, including the entire cloned region of the first exon, a large region in the 5′ portion of the intron and the 3′ portion of the second exon, but the 3′ portion of the intron and the 5′ portion of the second exon were dissimilar. Southern blots suggested that Valencia orange has two genes within each PE group. Full-length cDNA clones that shared 99% sequence identity with CsPME1 and CsPME3 were isolated. Both groups of PE genes were differentially expressed in tissues of Valencia orange, and in addition CsPME3 appeared to be ethylene-regulated. The deduced proteins of PE cDNA clones CsPME1 (63.5 kDa) and CsPME3 (56.3 kDa) were considerably larger than the PE protein we isolated from Valencia orange juice vesicles and also other mature plant PE proteins. The estimated size of group I (2.2 kb) and group II (2.0 kb) PE mRNAs also predicted a larger protein than was isolated from juice vesicles. Alignment of the mature tomato and mung bean PE proteins, the most N-terminal sequence we obtained from polypeptides derived from the 36 kDa PE isolated from juice vesicles and the deduced amino acid sequences of plant PE cDNA clones suggest that a post-translational cleavage event separates the variable N-terminus from the more conserved C-terminal domain of the mature PE protein.
    Type of Medium: Electronic Resource
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