Photosynthetic Characteristics of Four Wild Dendrobium Species in China

Photosynthetic physiology of Dendrobium nobile, Dendrobium pendulum, Dendrobium chrysotoxum, and Dendrobium densiflorum was studied. A bimodal diurnal variation of the net photosynthetic rate (Pn) was observed in the four Dendrobium species with the first peak [5.09 to 6.06 μmol (CO2) per m−2·s−1] ≈1100 hr and the second peak [3.83 to 4.58 μmol (CO2) per m−2·s−1] at 1500 hr. No CO2 fixation was observed at night. For all four Dendrobium species, the light compensation point (LCP) was 5 to 10 μmol·m−2·s−1, light saturation point (LSP) ranged from 800 to 1000 μmol·m−2·s−1, apparent quantum yield (AQY) was 0.02, and CO2 compensation points (CCP) and saturation point (CSP) were 60 to 85 μmol·mol−1 and 800 to 1000 μmol·mol−1, respectively. Carboxylation efficiency (CE) values ranged from 0.011 to 0.020. The optimum temperature for photosynthesis was between 26 and 30 °C. The measurement of Pn seasonal variation indicated that July to August had the higher Pn for Dendrobium species. Additionally, the chlorophyll a/b (Chl a/b) ratios of the leaves were 2.77 to 2.89. Measurement of key enzymes in the photosynthetic pathway indicated relatively high Ribulose-1,5-bisphosphate carboxylase (RuBPCase) and glycolate oxidase (GO) activities but very low phosphoenolpyruvate carboxylase (PEPCase) activities. It suggested that these four Dendrobium species are typical semishade C3 plants.

In vitro seed germination in Cymbidium elegans Lindl. and Dendrobium densiflorum Lindl. ex Wall. (Orchidaceae)

A comparative study of in vitro seed germination of two endangered orchid species, viz. Cymbidium elegans Lindl. and Dendrobium densiflorum Lindl. ex Wall., was carried out on Murashige and Skoog's (MS) medium, supplemented with different concentrations and combination of 6-benzylaminopurine (BAP) and á-Naphthalene acetic acid (NAA). The hormone-free MS medium and MS medium supplemented with various growth hormones were found effective for in vitro seed germination of both species. However, the seeds of these two species showed variation in their germination behavior. Hormone-free MS basal medium was found most effective for seed germination of D. densiflorum; whereas, basal medium supplemented with BAP (1mg/l) was effective for C. elegans. The seeds of D. densiflorum showed quick response in earlier germination, protocorm formation and further development into seedlings in comparison to C. elegans. In C. elegans, germination of immature seeds started after nine weeks of inoculation; whereas in D. densiflorum, the initiation of germination started after five weeks of culture. The variations in seed germination, protocorm formation and seedling differentiation in the two orchid species might be due to the differences in their genetic constitution and the presence of different endogenous growth stimulating substances present in their seeds. The present study has provided useful information for in vitro clonal mass multiplication of these commercially important orchid species. Key-words: growth hormone; in vitro study; orchid.DOI: 10.3126/botor.v6i0.2917 Botanica Orientalis - Journal of Plant Science (2009) 6: 100-102