Characteristics of starch from rice seeds modified by T-DNA insertion of ascorbate peroxidase 2

Starch is the main storage carbohydrate in rice seed. The amylose and amylopectin content differ among varieties. A transgenic rice line was obtained by T-DNA insertion of ascorbate peroxidase 2 (apx2), resulting in decrease of thousand kernel weight. In this study, starches were isolated from apx2 and wild type seeds. Morphology, physical and chemical properties of starch granules were analyzed. The seed micro-surface in apx2 showed distinct textures, compared with that of wild type. The morphology of starch granules in apx2 exhibited irregular shapes, while the wild type starch granules presented regular polyhedral shapes. Additionally, the length and width of starch granules in apx2 were significantly decreased, compared with that of wild type. Further analysis found that apx2 starch showed low crystallinity and high amylose with the methods of X-ray diffraction pattern, iodine binding and blue value analysis, fourier transform infrared (FT-IR) spectrum and thermogravimetric investigation. This study broadened our knowledge of relationship between antioxidant enzyme and rice seed starch formation.