Distribution Pattern of Cell Division Centers on the Epidermis of Stem Segments of Torenia fournieri during de Novo Bud Formation

The stem epidermis in Torenia fournieri, which has budding potentialialities, is composed of one cell layer which can be easily separated from the rest of the stem segment at different stages of bud formation. As the buds are formed directly from the epidermis, without intermediate callus formation, it is possible to observe simultaneously the cell division centers over the entire excised epidermal surface. The quantitative analysis at the 6-day stage of bud formation showed that the cell division centers do not have a random distribution on the epidermal surface. With respect to the length of the stem segment, the frequency of cell division centers increases toward the base which is also the direction of auxin transport. With respect to the width, the maximum number of division centers is observed on either side of the median zone. The median zone and the lateral zones have few division centers. An anatomical study showed that the zones with few division centers are the closest to underlying vascular tissue. A more uniform distribution of division centers can be obtained by addition of auxin to the medium.