Abstract:Changxuan 3S is a thermo-sensitive genetic male-sterile (TGMS) rice (Oryza sativa L.) with eui gene transferred from cultivar Pei’ai 64S. Variations in length and cell number of the uppermost internode were compared between the two cultivars during various stages of panicle initiation. The uppermost internode of Changxuan 3S elongated fastest during binucleate to anthesis stages, consequently it reached 2.1 times as long as that of Pei’ai 64S. Then it elongated slowly during pollen mother cell meiosis to binucleate stages and during 1 to 3 days after anthesis. During pollen mother cell meiosis to anthesis stages, parenchyma cells of the uppermost internodes of Changxua 3S and Pei’ai 64S increased by 3 759 and 3 134 in numbers, respectively, and with average cell lengths of 72.9 and 38 μm, respectively. The uppermost internode of Changxua 3S elongated due to cell division, especially cell elongation during pollen mother cell meiosis to anthesis stages.