Investigating starch from transgenic potato plants lacking starch branching enzyme I and/or glucan, water dikinase 1

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dc.contributor.advisorLloyd, Jamesen_ZA
dc.contributor.advisorVan der Vyver, Christellen_ZA
dc.contributor.authorGouws, Nina Ellenen_ZA
dc.contributor.otherStellenbosch University. Faculty of AgriSciences. Department of Genetics & Institute of Plant Biotechnology.en_ZA
dc.date.accessioned2024-02-29T15:11:56Z
dc.date.accessioned2024-04-26T13:01:42Z
dc.date.available2024-02-29T15:11:56Z
dc.date.available2024-04-26T13:01:42Z
dc.date.issued2024-03
dc.descriptionThesis (MScAgric)--Stellenbosch University, 2024. en_ZA
dc.description.abstractENGLISH ABSTRACT: Starch is the principal storage carbohydrate in plants where it is found in granules in plastids. It is the major calorie in the human diet and is an important feedstock in various industries. To improve the usefulness of native starch for different industrial applications, it must first undergo expensive chemical, physical or enzymatic treatments. Understanding starch biosynthesis can help to introduce modifications in planta with the aim of reducing such postharvest costs. Starch consists of two polymers, amylose and amylopectin, which are synthesised by multiple enzymes and are found in differing ratios where amylopectin normally constitutes the majority of the granule. Starch synthases elongate α-1,4 linked glucose chains to produce amylose. Starch branching enzymes can introduce α-1,6 branchpoints to form amylopectin which can be phosphorylated by glucan, water dikinases. There seems to be a relationship between the branching structure and phosphate incorporation as repression of STARCH BRANCHING ENZYME genes leads to increased granule bound phosphate. In this project, STARCH BRANCHING ENZYME I (SBEI) and GLUCAN, WATER DIKINASE 1 (GWD1) were repressed individually or simultaneously in potato using RNAi constructs. Repression of these enzymes resulted in changes to the amylose and phosphate contents. These alterations influenced granule morphology and gelling properties, but not freeze-thaw stability or starch digestibility. Rapid viscoamylography demonstrated that repression of SBEI increased phosphate content and peak viscosity. Starch pastes from SBEI transgenic plants also had improved paste clarity. GWD1 repression resulted in a decrease in phosphate content and peak viscosity. Simultaneous repression of SBEI/GWD1 resulted in higher amylose content and altered granule morphology with some multilobed starch granules being present. Despite the increase in amylose, a carbohydrate more resistant to digestion, no differences in digestibility of purified starch were found. This study adds to what is known about starch biosynthesis in potato tubers and demonstrates that starch can be modified in planta by targeting starch biosynthetic genes. Whether these changes ultimately result in improvement to end-products still needs to be investigated.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Stysel is die primêre stoorkoolhidraat in plante. Dit is die belangrikste kalorie in die menslike dieet en is ‘n belangrike komponent in verskeie nywerhede. Om die bruikbaarheid van stysel te verbeter vir industriële verbruik, moet die struktuur eers met duur chemiese, fisiese of ensiem behandeling verander word. Om hierdie na-oes koste te verminder, kan struktuurveranderings in planta aangewend word, dus is kennis van styselbiosintese belangrik. Stysel bestaan uit twee polimere, amilose en amilopektien, wat deur ‘n menigte ensieme saamgestel word. Styselsintases verleng α-1,4-gekoppelde glukosekettings om amilose te produseer. Styselvertakkingsensiemes kan amilose vertak deur α-1,6-takpunte by te voeg, waarby glukaan, waterdikinases fosfaat groepe kan aanheg. Daar blyk ‘n verhouding tussen die vertakkingsstruktuur en fosfaat inhoud, maar die ensieme verantwoordelik vir hierdie eienskappe is nog nie saam bestudeer nie. In hierdie studie is STARCH BRANCHING ENZYME I (SBEI) en GLUCAN, WATER DIKINASE 1 (GWD1) in aartappel afsonderlik of gelyktydig onderdruk deur van RNAi-konstrukte gebruik te maak. Onderdrukking van hierdie eniseme het veranderinge in die amilose en fosfaat inhoud tot gevolg gehad. Hierdie wysigings het styselkorrelmorfologie en gel eienskappe beïnvloed, maar nie stabiliteit in vries-ontdooi toetse of die verteerbaarheid van die stysel nie. Onderdrukking van SBEI het gelei tot hoër fosfaat inhoud en piek viskositeit, asook ‘n meer deursigtige gel. Onderdrukking van GWD1 het gelei tot ‘n afname in fosfaat inhoud asook in piek viskositeit. Gelyktydige onderdrukking van SBEI/GWD1 het gelei tot hoër amilose inhoud en die ontstaan van veellobige styselkorrels. Ten spyte van die toename in amilose, ‘n koolhidraat wat meer weerstandig is teen verteringsensieme, is geen verskille in die verteerbaarheid van suiwer stysel gemerk nie. Hierdie studie dra by tot die kennis van styselbiosintese in aartappels en toon dat wysigings tot die styselstruktuur aangewend kan word in planta deur gene betrokke in styselbiosintese te teiken. Dit moet egter nog ondersoek word of hierdie veranderinge wel tot die verbetering van eindprodukte lei.af_ZA
dc.description.versionMastersen_ZA
dc.format.extentix, 58 pages : illustrations (some color)en_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/130312
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshStarch -- Biosynthesisen_ZA
dc.subject.lcshGene expressionen_ZA
dc.subject.lcshStarch branching enzyme -- Classificationen_ZA
dc.subject.lcshPotato starchen_ZA
dc.subject.lcshUCTDen_ZA
dc.titleInvestigating starch from transgenic potato plants lacking starch branching enzyme I and/or glucan, water dikinase 1en_ZA
dc.typeThesisen_ZA
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