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Molecular Characterization of Hexose Transporter in Sugar Accumulation of Papaya Fruit During Maturation and Ripening

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Title:Molecular Characterization of Hexose Transporter in Sugar Accumulation of Papaya Fruit During Maturation and Ripening
Authors:Sangwanangkul, Peerapong
Date Issued:2007
Abstract:Papaya glucose uptake during fruit development was studied by comparing 14C-glucose uptake of mesocarp slices between two cultivars, ‘Sunset’ and UH801 (low sugar line) in two seasons, September-December, 2003 and April-July, 2004. ‘Sunset’ papaya fruit, though one third the weight of UH801, had higher total soluble solids (TSS), total sugar, and dry weight (DW) than UH801. In 2003, both cultivars reached the color break stage at the same time, 125 days after anthesis (DAA), but flesh color, TSS, and DW of ‘Sunset’ fruit began to increase 111 DAA, one to three weeks before UH801. In 2004, both cultivars started to develop skin and fresh color and accumulate TSS, total sugar, and DW at 139 DAA. In 2003, glucose uptake in ‘Sunset’ fruit was lower than for UH801, but found to be higher in 2004. The pattern of 14C-glucose uptake by ‘Sunset’ papaya flesh discs was divided into three fruit growth phases during fruit maturation. Uptake was initially low during the first, 90-97 DAA (2003) and 90-111 DAA (2004), and last phase, after 132 DAA for both years and high 97-132 DAA and 11-132 DAA in 2003 and 2004, respectively. The maximum glucose uptake in ‘Sunset’ was found at 118 DAA in both years to be 1,367 and 2,140 pmol mg protein-1h-1, respectively. Papaya hexose transporter appeared to be an energy-dependent cotransporter. Hexose transporter activity was detected in both varieties but 14C-glucose uptake did not appear to correlate with papaya sugar accumulation. Hence, the role of invertase in phloem unloading may be a more important factor in determining fruit sugar levels at harvest.
The 1,642 bp cDNA of the first Carica papaya hexose transporter (CpHT1) has been cloned. The sequence of CpHT1 cDNA matched part of the sequence on the papaya genome supercontig_1226 which consisted of 3,218 bp with four exons and three introns. The full length CpHT1 mRNA was predicted to be 1,732 bp and encoded a 523 amino acids long peptide. The predicted polypeptide was estimated to be 57.48 kDa and contained 12 transmembrane helices with both amino and carboxyl terminals located in the cytosol.
URI:http://hdl.handle.net/10125/56210
Appears in Collections: Ph.D. - Horticulture


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