Developmental Changes in Endogenous Abscisic Acid Concentrations and Asymbiotic Seed Germination of a Terrestrial Orchid, Calanthe tricarinata Lindl.

Abstract

<jats:p>Changes in endogenous abscisic acid (ABA) concentrations were investigated in developing seeds and the pretreated seeds of <jats:italic>Calanthe tricarinata</jats:italic>, a hard-to-germinate terrestrial orchid. ABA concentration was as low as 2.16 to 2.26 ng·mg<jats:sup>−1</jats:sup> fresh weight at the proembryo stage [60 to 90 days after pollination (DAP)] and then continuously increased to 11.6 ng·mg<jats:sup>−1</jats:sup> fresh weight at 210 DAP. Seed maturation was accompanied by a dramatic decrease in water content and a prominent accumulation of protein and lipid bodies within the embryo proper. The optimum time for asymbiotic seed germination was obtained from immature seeds at 150 DAP. At this stage, the embryo proper reached its maximum size, and the seedcoat became dehydrated and gradually shrunk into a thin layer. By 180 DAP, seed germination declined sharply as seed approached maturity. Mature seeds pretreated with ultrasound (45 min), 1% NaOCl (45 to 60 min), or 1N NaOH (45 min) were effective in improving the germination percentage and lowering seed ABA concentrations. Our results suggest that high concentrations of endogenous ABA in orchid seeds may play a critical role in arresting embryo growth and in preventing seed germination.</jats:p>

Germination of mature seeds of Calanthe tricarinata Lindl., an endangered terrestrial orchid, by asymbiotic culture in vitro

“…The germination frequency of fully matured seeds was much lower and only a few seeds germinated. Lee et al (2007) also noted that scarification, for example, by prolonged treatment with chemical solutions and ultrasound stimulated the germination of fully matured seeds and resulted in frequencies of seed germination (32% to 39%) similar to that of immature seeds.…”

“…Kano (1972) reported that seed germination of members of the genus Calanthe from temperate regions is the most difficult among all terrestrial species of orchid studied. There are several reports of the propagation of the genus Calanthe by the asymbiotic germination of seeds Mii 1988, 1995a, b;Fukai et al 1997;Park et al 2000;Lee et al 2007). Various strategies, such as presoaking seeds in water (Mii and Kako 1974), organic solvent (Mii 1978), phytohormones (Miyoshi and Mii 1995a), NaOCl solution (Miyoshi and Mii 1995b), and pretreatment of ultrasonication (Miyoshi and Mii 1988), and the addition of a polyphenol absorbent to the medium (Miyoshi and Mii 1995b) have been employed in efforts to improve the seed germination and/ or protocorm formation of temperate species of Calanthe.…”

“…Various strategies, such as presoaking seeds in water (Mii and Kako 1974), organic solvent (Mii 1978), phytohormones (Miyoshi and Mii 1995a), NaOCl solution (Miyoshi and Mii 1995b), and pretreatment of ultrasonication (Miyoshi and Mii 1988), and the addition of a polyphenol absorbent to the medium (Miyoshi and Mii 1995b) have been employed in efforts to improve the seed germination and/ or protocorm formation of temperate species of Calanthe. Recently, Lee et al (2007) reported that collected seeds of C. tricarinata at various stages of the formation and maturation of seeds and the frequency of germination of immature seeds 150 d postanthesis reached approximately 30%. The germination frequency of fully matured seeds was much lower and only a few seeds germinated.…”

“…Temperature might be another factor that controls the germination of orchid seeds (Rasmussen 1995). Although C. tricarinata grows in cool conditions in natural habitats, investigations of seed germination of this species at 25°C have been limited (Lee et al 2007). The successful stimulation of germination of orchid seeds by cytokinins has been reported for some members of the genus Cypripedium.…”

“…In the present study, we evaluated the effects of illumination, temperature, and the addition of plant growth regulators to the medium on the asymbiotic germination of mature seeds of C. tricarinata, hoping to exceed the maximum frequency of germination of immature seeds (Lee et al 2007). We discuss the significant role of a reproducible protocol for the establishment of seedlings from seeds by asymbiotic culture in this species.…”