Distribution of Nuclei of Different Ploidy Levels during Ovule, Seed and Protocorm Development in <i>Phalaenopsis aphrodite</i> subsp. <i>formosana</i> (Orchidaceae)

Abstract

Distribution of nuclei of different ploidy levels was studied at different developmental stages in the embryonic tissue of the ovule, seed and protocorm of Phalaenopsis aphrodite subsp. formosana (Miwa) E.A. Christ. by a combination of flow cytometry and fluorescence microscopy with Apo Tome Slider. Three stages of ploidy patterns were identified in the ovular tissue at different days after pollination (DAP). Firstly, between pollination and fertilization (0 to 50 DAP), 2C nuclei were dominant over 4C nuclei and resulted in low level of cycle value. Secondly, between fertilization and seed maturation (50 to 110 DAP), amount of 4C nuclei increased rapidly, maintained at a high level and then decreased gradually to a low level. Small amount of 8C nuclei was also detected at this stage. Thirdly, at seed maturation (110 to 130 DAP), 2C nuclei became dominant over 4C nuclei again and the cycle value remained at a low but significant level at this stage. After seed sowing, nuclei with ploidy levels of 2C, 4C and 8C were observed in the developing protocorms as early as at 4 DAS (days after sowing). Nuclei with high ploidy levels (8C and 16C) increased gradually until 40 DAS in this study. Significant level of cycle value at this stage of protocorm development indicated the presence of endopolyploidy. 4,6-diamido-2-phenylindol (DAPI) staining showed large and prominent nuclei in the basal portions of the mature seeds before sowing and in the developing protocorms at 20 DAS. These findings clearly demonstrate the occurrence of different distribution patterns of nuclei with different ploidy levels during ovule, seed and protocorm de-velopment in Phalaenopsis aphrodite. These observations will provide fundamental information for further studies in Phalaenopsis orchids.