Early events in rice somatic embryogenesis: changes in cortical microtubule distribution and orientation

The changes in the microtubular pattern during the first few days of somatic embryo induction were studied using the rice scutellum epithelium system. A clear difference in the distribution and orientation of the microtubules could be found as early as 12 h after culturing. In the control treatment, the microtubules tended to congregate near the terminal part of the cells and had an oblique to transverse orientation with respect to the long axis of the cells. In the hormone-treated explants, the microtubules were more evenly distributed throughout the cells as compared to the control treatment. The microtubules initially had an oblique orientation similar to the control. However, by 16 h, the majority of microtubules were aligned parallel to the long axis of the cells. The scutellum epithelial cells in both the control- and hormone-treated explants divided periclinally at about 48 h. In the control treatment, the scutellum epithelial cells gradually became vacuolated over time, while the hormone-treated explants remained densely cytoplasmic. The fluorescence staining intensity gradually declined in the control, whereas a distinct staining pattern of microtubules remained in the hormone-treated explants.