Browsing by Subject "Sucrose"

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    Identification and characterization of three Arabidopsis sugar insensitive genes
    (2008-10) Huang, Yadong
    Carbohydrates have signaling functions in regulating gene expression, metabolic pathways and developmental processes. Eukaryotic organisms have evolved conserved and novel mechanisms for sensing and responding to sugars. Plant sugar response pathways are complex and exhibit cross-talk with other response pathways. Sugar responses and signaling pathways have been studied via physiological, biochemical and genetic approaches. Genetic screens have identified sugar response mutants with altered seedling growth phenotypes. The Gibson lab has isolated an array of sugar insensitive (sis) mutants by screening mutagenized Arabidopsis seeds on high concentrations of sugars. The identification and characterization of three of the SIS genes, SIS7, SIS3 and SIS8, are presented here. SIS7 is allelic to NCED3/STO1, an abscisic acid (ABA) biosynthetic gene, which is involved in drought and salt stress responses. Lateral root (LR) development of sis7 mutants is resistant to the inhibitory effects of osmotica. Transcriptomic analysis revealed that a set of auxin-related genes are expressed at lower levels in sis7 seeds than in wildtype seeds when incubated with glucose, suggesting that these genes may be involved in controlling LR development by both ABA and auxin. SIS3 encodes a RING finger protein that functions as an E3 ligase in in vitro ubiquitination assays. The sis3 seeds display wild-type germination responses to ABA and GA. However, the root growth of sis3 mutants has slightly reduced sensitivity to ABA. The sis8 mutants have decreased sensitivity to high sugars and hyperosmolarity. Positional cloning of sis8 revealed that the mutation is in a putative mitogen-activated protein kinase kinase kinase gene. Seed germination assays indicate that sis8 mutants have wild-type sensitivity to ABA and GA, whereas overexpression of SIS8 causes slight hypersensitive responses. Potential interaction partners of SIS8 have been identified via yeast two-hybrid screening. A T-DNA insertion in the gene encoding one potential SIS8- interacting protein, UGT72E1, causes a sis phenotype. Further studies of the SIS3 and SIS8 genes will provide more insight into the mechanisms of sugar signaling in plants.
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    Sucrose crystallinity quantification using FTIR spectroscopy
    (2014-10) Mortenson, Aimee Kwong
    Understanding sucrose crystallinity is important especially as the food industry has reduced sugar content in products. Robust quantification methods determine crystallinity effects from formulation and/or processing changes. Differential Scanning Calorimetry (DSC) quantifies crystallinity within products, albeit requiring sample destruction. Fourier Transform Infrared (FTIR) spectroscopy can quantify different materials and has the potential of mapping crystallizing areas within a complex food matrix. Additionally, this method can be used to quantify sucrose crystallinity by a non-destructive, rapid means.Currently the methods used to quantify for sucrose crystallinity have been explored in pharmaceutical, lower moisture systems, where complex food matrices are not a factor. The objectives were to create a FTIR method to quantify the amount of crystalline sucrose in mixtures at various concentrations and to determine feasibility of spatial analysis capabilities using FTIR microscope methods.The development of the method was built using model systems of sucrose and carbohydrate blends. Crystallinity was measured via both FTIR and DSC. Samples were freeze-dried and held at different humidity levels to determine which IR peaks were independent of moisture content. IR spectral peaks that correlated best with the DSC measured sucrose crystallinity content were identified. Different calibration methods were concurrently used to obtain the best statistical fit using TQ Analyst® software. FTIR spatial analyses were performed on samples to assess feasibility of the method and commercialized baking mixes were tested to determine efficacy of the bulk method on complex food matrices.Three regions of interest (1087 cm-1, 991 cm-1, and 909 cm-1) were found to have the best Partial Least Squares (PLS) correlation to the crystallinity percentage. A Performance Index of 96.3 and a Root Mean Square Error of Prediction 0.925 were achieved with the three regions. These results show the potential of a robust method to quantify heterogeneous microdomains within foods, without interference from complex matrices. The three regions were statistically comprehensive at defining the variables as a bulk method. The spatial analysis using the FTIR microscope was affected by sucrose orientation, beam intensity, and shifts in peaks. A lower magnification spatial method would be a more applicable use of this method in an inline FTIR technology. The future application of this technology is to combine observed microdomains and correlate them to events such as stickiness or drying rates, for example.