Botanical Studies (2008) 49: 139-146.
Present address: Botany Department, National Museum of
Natural Science, Taichung, Taiwan, ROC.
Corresponding author: E-mail: email@example.com.
tw; Tel: 886-2-27892701; Fax: 886-2-27827954.
Embryology of Phalaenopsis amabilis var. formosa:
, Edward C. YEUNG
, Nean LEE
, and Mei-Chu CHUNG
Institute of Plant and Microbial Biology, Academia Sinica, 11529, Taipei, Taiwan, ROC
Department of Biological Sciences, University of Calgary Calgary, Alberta T2N 1N4, Canada
Department of Horticulture, National Taiwan University, No 1, Sec. 4, Roosevelt Rd., 106, Taipei, Taiwan, ROC
(Received November 30, 2006; Accepted October 17, 2007)
Phalaenopsis amabilis var. formosa is an endemic epiphytic orchid variety native to Taitung
and Lanyu of Taiwan. A
-shaped, four-celled embryo is produced by two successive cell divisions of a
zygote. Soon after, two of the four cells toward the micropyle enlarge and divide two more times resulting in
the formation of eight tubular suspensor cells. The suspensor cells are highly vacuolated; the bottom tier of
suspensor cells elongates towards the micropyle, and the upper tier elongates towards the chalazal end of the
seed. During the early stages of embryo development, lipid droplets appear in the elongating suspensor cells
and disappear soon afterwards, indicating the suspensor functions in nutrient uptake and as a temporary food
storage site for the developing embryo. In the mature seed, a differentiated apical zone containing the rela-
tively small cells can be seen in the embryo proper. Protein and lipid bodies are the main storage products in
the embryo proper cells. The results of Nile red staining indicate that a cuticular layer is present only on the
surface walls of the embryo proper, but is absent from the suspensor cell wall Cuticular material is also pres-
ent in the outermost layer of the seed coat and persists through seed maturation.
Keywords: Embryo; Orchid; Phalaenopsis amabilis var. formosa; Suspensor.
The genus Phalaenopsis (Orchidaceae) comprises about
63 species that have produced numerous attractive hybrids
and cultivars (Christenson, 2001). Of these, Phalaenop-
sis amabilis var. formosa is an endemic epiphytic orchid
variety native to Taiwan¡¦s Taitung and Lanyu Island (lat.
22¢X N, long. 121¢X3¡¦ E) (Lin, 1988). During the past few
decades, P. amabilis var. formosa has been used extensive-
ly in breeding for Phalaenopsis hybrids, and now it is one
of the most important species for the floriculture industries
Orchid seeds are tiny, and most contain a globular-
shaped embryo and lack a well-defined endosperm (Arditti,
1992; Yam et al., 2002). Additionally, the orchid embryos
have a diversified suspensor morphology. This led Swamy
(1949) to propose a classification scheme for orchid em -
bryo development based in part on the form and the pattern
of suspensor development. According to Swamy (1949),
the suspensor of Phalaenopsis contains eight filamentous
cells which elongate toward the chalazal end of the seed,
surrounding the embryo proper. Although the general pat-
tern of embryo developmental is known, detailed structural
information is not available.
The objectives of this study were to document the
anatomical events in the embryo development of P. ama-
bilis var. formosa from fertilization to seed maturity, and
to detail the formation of the suspensor. The information
presented here will provide valuable background informa-
tion for both propagation and future molecular biology
studies on the embryogenesis of Phalaenopsis species.
MATERIALS AND METHODS
Plants of Phalaenopsis amabilis var. formosa were
grown in greenhouses at National Taiwan University in
Taipei, Taiwan. To ensure a good fruit set and seed quan-
tity, flowers were hand pollinated. Developing fruits were
harvested at regular intervals after pollination. Approxi-
mately 50 developing fruits were gathered for this study.
Transverse sections, approximately 2 mm thick of de-
veloping and mature fruits were fixed in 2.5% glutaralde-
hyde and 1.6% paraformaldehyde buffered with 0.05 M
phosphate buffer, pH 6.8, for 24 h at 4¢XC. After fixation,