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Investigating the role of sucrose phosphate synthase and hexokinase in carbon sink strength. Lazarova, Sofiya


The production, transport and assimilation of organic carbon ultimately drive the growth of plants. In this work, two enzymes, Sucrose Phosphate Synthase (SPS) and Hexokinase (HXK), prominent in their role of carbon production in the form of sucrose at the source, have been examined for their role at the sink, where carbon is assimilated. It has been postulated that the presence of sucrose-forming enzymes in the sink serves a function to reform sucrose from apoplastic cleavage or partake in a “futile” cycle of sucrose cleavage and such that small changes in metabolite enable large changes in sink carbon strength. In order to determine if SPS is involved in carbon sink strength, A. thaliana TDNA insertional lines and P. trichocarpa RNAi stem and developing xylem with decreased SPS transcript expression were analyzed. It was determined that loss of SPS transcript generally increases soluble sugars: sucrose, glucose and fructose, in the leaf and stem as well as starch in the leaf. Structural carbohydrates were generally unaffected and Klason soluble lignin decreased. Similarly, A. thaliana TDNA insertional lines with decreased HXK transcript expression were utilized to determine the role of HXK using stem tissue as a carbon sink model. Soluble sugars mainly increased in the leaf of athxk3 TDNA insertional line whereas starch increased in both leaf and stem of the same line. Interestingly, structural carbohydrate levels of the cell wall were perturbed in HXK TDNA insertional lines. The results were found to be consistent with the postulated roles of SPS and HXK that predict a function in sucrose formation from apoplastic cleavage, which allows for fine-tuning of major intracellular metabolites and adjustment of sink strength.

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