| The thermal properties of starch during gelatinization are important characters to food and non-food industries. The size distribution of starch granules are also critical in both industrial processing and application. So for, several studies on the thermal properties of maize starch have been'done only in limited starch-modified genotypes or in uncommon genetic backgrounds. There rarely has any information about the effects of genetic backgrounds on the thermal properties of maize starch. Few investigation have been conducted on the thermal variation of starch in normal maize. It is unclear whether the granule size of starch would influence the thermal properties. Few investigation are involved in evaluating the effects of starch-modified genes on the granule size of maize starch under a common background and with a large scale samples.In this study, the thermal properties of four single mutants: ae/ae, du/du, su2/su2 and wx/wx, five double mutants: ae/ae du/du, ae/ae wx/wx, du/du su/su2, du/du wx/wx, and su2/su2 wx/wx, and their normal counterparts were evaluated in two different genetic backgrounds (Oh43 and B37). The variability for thermal properties of starch from 35 tropical and semitropical normal populations was also estimated. Enthalpy (AH), peak onset (To), peak maximum (Tp), peakhigh (Hp) and peak conclusion (Tc) were determined with Differential Scanning Calorimetry (DSC). The temperature range (Tr) of gelatinization was calculated as Tc-To. The granule size of starch in nine genotypes was measured by a Brinkmann Particle Size Analyzer (PSA) with laser light. The total number of particles counted in each replicate varied from 22,107 to 85,282.According to this investigation, it was found that different starch-modified genes highly significantly influenced the thermal properties of starch. The wx starch possessed the Tp of 73℃ and the AH of 10.95 j/g, and the ae starch had the Tp of 81.35℃ and the AH of 11.05 j/g, all of which were higher than the normal. The Tp of all homological su2 genotypes, either in single or in double mutants, had as over 10℃ low as the normal. Except for the du/du wx/wx, the other double mutants had much lower AH , ranging from 1.8 (du/du wx/wx) to 6.26 (su2/su2 wx/wx) j/g. The interactions on the thermal properties between different genes were detected. The su2 gene may have an eptstatic effect to the du and wx on the Tp. It was found that different genetic backgrounds significantly affect the thermal properties. Oh43 always had a high values in each measured properties. Among 35 populations, highly significant differences for all measured properties were observed. Means of Tp was 71.0℃, ranging 70.1-73.9℃. The Tr varied between 9.8 and 13.0℃. Average H was 10.5 j/g with a range of 8.2-12.3 j/g. The remarkable correlation of the granule size with the thermal properties was detected. As the size increased, AH raised, Tp decreased, and Tr narrowed in the same background and the same genotypes. A wide variation of starch granule size amongnine different genotypes was found, which varied from 9.75 to 15.83 um. Except wx gene, the other genes, such as ae, du and su2, significantly declined the granule size.These results suggest that utilization of starch-modified genes for improving starch qualities is an efficient and available way and implies that the choice of backgrounds is necessary in maize breeding for starch qualities. 35 populations surveyed in this study may be valuable resources for improving the thermal properties of maize starch. These investigations also revealed that the granule size of starch is one of factors that affect thermal properties of starch and demonstrated that the starch-modified gene may play a virtually role in determining the granule size of starch. All of these discoveries will have important theoretical and practical significance in maize breeding for starch quality.
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