Effects Of Suppression Of Starch Branching Enzyme Gene Expression On Caryopsis Development In Rice

In rice, amylose content is known as the critical factor to influence not only the quality but also the application. The amylose content can be regulated by changing starch branching enzyme gene expression. In this study, rice varieties Te-qing, Wu-xiang9915and Guang-ling-xiang-nuo with different amylose content and their transgenic rice lines were used as materials to study the effects of suppression of starch branching enzyme gene expression on caryopsis development. The appearance quality, endosperm cell number, endosperm development, starch granule morphology and accumulation were investigated in developing and mature caryopsis. This study might be very useful for improving rice quality by transgenic techniques. The main results were shown as followings.Effects of suppression of starch branching enzyme gene expression on rice appearance quality. The appearance quality of mature kernels changed in some transgenic rice lines with suppression of starch branching enzyme gene expression. Compared with the wild type rice, transgenic rice lines showed the decrease of kernel width, thickness, weight, volume and volume weight, and the increase of water content. The rank order of the effects on rice appearance quality, from strong to weak, was the suppression of starch branching enzyme1/3, the suppression of starch branching enzyme3, and the suppression of starch branching enzyme1. The rank order of the effects on rice variety, from strong to weak, was Te-qing with high amyose content, Wu-xiang9915with mediate amylose content, and Guang-ling-xiang-nuo with zero amylose content.Effects of suppression of starch branching enzyme gene expression on rice endosperm development. The endosperm cell number decreased in some transgenic rice lines with suppression of starch branching enzyme gene expression. The rank order of the effects on endosperm cell number, from strong to weak, was the suppression of starch branching enzyme1/3, the suppression of starch branching enzyme3, and the suppression of starch branching enzyme1. The effects on endosperm cell number were very significant in rice varieties Te-qing and Guang-ling-xiang-nuo. Compared with the wild type rice, some transgenic rice lines showed the decrease of grain filling degree and starch granule number in endosperm cell. Some starch morphology changed in some transgenic rice lines.Caryopsis development dynamics of high-amylose rice TRS with suppression of starch branching enzyme1/3. The developing caryopses of a high-amylose transgenic rice line TRS and its wild type Te-qing (TQ) were measured. At the early development stage, Te-qing and TRS rice showed similar kernel shape, weight, volume, volume weight and water content. Compared with TQ, TRS rice showed lower kernel thickness, weight, volume and volume weight, and higher water content after10days of flowering. The endosperm cell layer number and subaleurone layer cell thickness were significantly lower in TRS than in Te-qing at18day of flowering.Accumulation and distribution of heterogeneous starch granule during endosperm development in high-amylose rice TRS. TRS endosperm exhibited oval, internal hollow, elongated and polygonal shapes. Semithin section observation showed that oval and polygonal starch granules were mainly distributed in the center of endosperm, elongated and internal hollow starch granules were mainly distributed in subaleurone layer cells. The elongated starch granule began to appear at4day after flowering, and rapidly increased after8day of lowering. The rank order of the distribution of elongated starch granule, from high to low, was the lateral and abdominal subaleurone layer cells, dorsal subaleurone layer cells. The internal hollow starch granule began to appear at8day after flowering, and rapidly increased with endosperm development. The rank order of the distribution of internal hollow starch granule, from high to low, was the lateral, abdominal, and dorsal subaleurone layer cells.