Browsing by Author "Van Staden, J."

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    Malic acid distribution and degradation in grape must during skin contact : the influence of recombinant malo-ethanolic wine yeast strains
    (South African Society for Enology and Viticulture, 2005) Van Staden, J.; Volschenk, H.; Van Vuuren, H. J. J.; Viljoen-Bloom, M.
    Wine acidity plays an important role in determining wine quality and ensuring physiochemical and microbiological stability. In high-acid wines, the L-malic acid concentration is usually reduced through bacterial malolactic fermentation, while acidulation in low-acidity wines is usually done during final blending of the wine before bottling. This study showed that skin contact did not influence the relative concentration of L-malic acid in the pulp and juice fractions from Colombard, Ruby Cabernet and Cabernet Sauvignon grape musts, with 32%-44% of the L-malic acid present in the pulp fraction. Four recombinant malo-ethanolic (ME) Saccharomyces wine yeast strains containing the malic enzyme (mae2) and malate transporter (mael) genes of Schizasaccharomyces pombe, effectively degraded the L-malic acid in both the juice and pulp fractions of all three cultivars, with a complete degradation of malic acid in the juice fraction within 2 days.
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    Transformation of potato (cv. Late Harvest) with the potato leafroll virus coat protein gene, and molecular analysis of transgenic lines
    (Academy of Science for South Africa, 1998) Murray, S. L.; Burger, J. T.; Oelofse, D.; Cress, W. A.; Van Staden, J.; Berger, D. K.
    Potato leafroll virus (PLRV) is one of the most destructive potato viruses in South Africa. In order to establish resistance against PLRV in the potato cultivar Late Harvest, the coat protein (CP) gene of a South African isolate of the virus was isolated, cloned into the plant transformation vector pBI121 and inserted into potatoes using Agrobacterium tumefaciens-mediated transformation. Six plantlets, which appeared to be phenotypically normal, were regenerated from leaf disks under kanamycin selection. These lines were analysed for stable transgene insertion and expression. The presence of the PLRV CP, uidA (GUS) and nptII (kanamycin resistance) genes were shown using PCR! Southern blot analysis verified that the PLRV CP gene had been inserted into the genome of the transgenic potato lines. Coat protein could not be detected, but RNA dot blots demonstrated PLRV CP gene expression at the mRNA level. Expression of the uidA gene was investigated using a fluorometric assay, and it was observed that lines containing the PLRV CP gene in the antisense orientation exhibited GUS activity.