Browsing by Author "Oberlander, Kenneth"

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    A molecular phylogenetic assessment of Oxalis L. section Angustatae subsection Lineares using trnL-trnF sequence data
    (Stellenbosch : Stellenbosch University, 2003-03) Oberlander, Kenneth; Dreyer, L. L.; Bellstedt, D. U.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: The phylogenetic relationships and taxonomic status of South African Oxalis L. species are highly unresolved, both regionally and with regard to precise placement within the genus as a whole. Studies based exclusively on morphological and palynological characteristics have hitherto proved only partially successful in resolving natural groupings among the indigenous taxa of the region. Recent studies involving a few native taxa have indicated the plastid trnL-trnF non-coding DNA region as useful for the purposes of reconstructing phylogenetic relationships within the genus. The present study addressed the taxonomic monophyly and relationships of the highly unresolved section Angustatae subsection Lineares, using DNA sequence data. The phylogenetic reconstruction of southern African Oxalis species renders five of the subsections of section Angustatae sensu Salter (1944) polyphyletic, three of them conclusively so. The members of subsection Lineares are split between three clades, two of them with strong bootstrap support. None of these three clades consists exclusively of species of subsection Lineares. Likewise four of the seven assemblages of related taxa within subsection Lineares sensu Salter (1944) are not retrieved as monophyletic. Pollen data sensu Dreyer (1996) supports the clades retrieved in this study, whereas very few morphological characters could be plotted as potential synapomorphies for these clades. The resultant phylogenetic reconstruction thus supports palynological data of this subsection, and indicates the urgent need for a revision of the current morphological classification of Salter (1944).
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    Mutations in glucan, water dikinase affect starch degradation and gametophore development in the moss physcomitrella patens
    (Nature Research, 2019) Mdodana, Ntombizanele T.; Jewell, Jonathan F.; Phiri, Ethel E.; Smith, Marthinus L.; Oberlander, Kenneth; Mahmoodi, Saire; Kossmann, Jens; Lloyd, James R.
    The role of starch degradation in non-vascular plants is poorly understood. To expand our knowledge of this area, we have studied this process in Physcomitrella patens. This has been achieved through examination of the step known to initiate starch degradation in angiosperms, glucan phosphorylation, catalysed by glucan, water dikinase (GWD) enzymes. Phylogenetic analysis indicates that GWD isoforms can be divided into two clades, one of which contains GWD1/GWD2 and the other GWD3 isoforms. These clades split at a very early stage within plant evolution, as distinct sequences that cluster within each were identified in all major plant lineages. Of the five genes we identified within the Physcomitrella genome that encode GWD-like enzymes, two group within the GWD1/GWD2 clade and the others within the GWD3 clade. Proteins encoded by both loci in the GWD1/GWD2 clade, named PpGWDa and PpGWDb, are localised in plastids. Mutations of either PpGWDa or PpGWDb reduce starch phosphate abundance, however, a mutation at the PpGWDa locus had a much greater influence than one at PpGWDb. Only mutations affecting PpGWDa inhibited starch degradation. Mutants lacking this enzyme also failed to develop gametophores, a phenotype that could be chemically complemented using glucose supplementation within the growth medium.
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    Repression of sex4 and like sex four2 orthologs in potato increases tuber starch bound phosphate with concomitant alterations in starch properties physical
    (Frontiers Media, 2018-07-23) Samodien, Ebrahim; Jewell, Jonathan F.; Loedolff, Bianke; Oberlander, Kenneth; George, Gavin M.; Zeeman, Samuel C.; Damberger, Fred F.; Van Der Vyver, Christell; Kossmann, Jens; Lloyd, James R.
    To examine the roles of starch phosphatases in potatoes, transgenic lines were produced where orthologs of SEX4 and LIKE SEX FOUR2 (LSF2) were repressed using RNAi constructs. Although repression of either SEX4 or LSF2 inhibited leaf starch degradation, it had no effect on cold-induced sweetening in tubers. Starch amounts were unchanged in the tubers, but the amount of phosphate bound to the starch was significantly increased in all the lines, with phosphate bound at the C6 position of the glucosyl units increased in lines repressed in StSEX4 and in the C3 position in lines repressed in StLSF2 expression. This was accompanied by a reduction in starch granule size and an alteration in the constituent glucan chain lengths within the starch molecule, although no obvious alteration in granule morphology was observed. Starch from the transgenic lines contained fewer chains with a degree of polymerization (DP) of less than 17 and more with a DP between 17 and 38. There were also changes in the physical properties of the starches. Rapid viscoanalysis demonstrated that both the holding strength and the final viscosity of the high phosphate starches were increased indicating that the starches have increased swelling power due to an enhanced capacity for hydration.