Highly endoreduplicated floral organs of somaclonal variants in clonally propagated Phalaenopsis ‘Spring Dancer’

Abstract

A micropropagation system is essential for obtaining elite clones of Phalaenopsis in the floricultural industry; however, somaclonal variation frequently occurs during long-term micropropagation, which reduces the uniformity and quality of clonally propagated plants. To detect the factors influencing this variation and thus obtain high-quality, uniform Phalaenopsis plants, we analyzed somaclonal variants in the Phalaenopsis ‘Spring Dancer’ (SD) variety collected from an orchid farm, which were grouped into three types according to flower morphology (SD-N, SD-V1, SD-V2). Morphological differences were observed between all SD groups; in particular, the diameter of the petal and thickness of each organ were significantly larger in the variants than SD-N (normal) plants. Both SD variant groups showed the same ploidy level as that of SD-N. The degree of endoreduplication of the petals and flower stalks was higher in the variants (4C–16C) than in SD-N (2C–8C). Cell area was increased and the shape of epidermal cells was changed in both variants. Expression levels of MADS box transcription factor (MADS4) of the flowers were higher than those of the leaves in the variants. Among the three flower organs, MADS4 expression was the highest in the petals of SD-V2. These results revealed that MADS4 is involved in the modification of flower morphology in somaclonal SD variants. High ploidy 2 (HPY2) expression was highest in the flowers of SD-V1, whereas its expression in the leaf was similar to that of SD-N. Among the various flower organs, HPY2 expression was highest in the lips of SD-V1.