Propagation of Ornamental Plants
7(2): 89-96, 2007
GROWTH AND PHOTOSYNTHESIS OF DENDROBIUM CANDIDUM WALL. EX LINDL.PLANTLETS CULTURED PHOTOAUTOTROPHICALLY
Yulan Xiao1,2*, Yongtai Zhang2, Kang Dang2, and Dongshuang Wang2
1College of Life Science, Capital Normal University, Beijing 100037, China, *Fax: + 86-10-68902328, *E-mail: email@example.com
2Yangtze Delta Region Institute of Tsinghua University, Jiashan, Zhejiang 314100, China
Dendrobium candidum, a peculiar and valuable Chinese herb and Crassulacean Acid Metabolism (CAM) plant, was cultured for 45 days on a sugar-free modified Murashige and Skoog (MS) medium in Magenta-type vessels with the number of air exchanges of the vessel (NAE) being 3.2 h-1, at a photosynthetic photon flux (PPF) of 80 mmol m-2 s-1. A factorial experiment was designed with two levels of CO2 concentration, 400 mmol mol-1 (PA treatment) and 1000 mmol mol-1 (PAC treatment) in the culture room during the photoperiod. The plantlet growth, photosynthesis and state of stomata were compared to the plantlets cultured on sugar-containing MS medium with PPF of 50 mmol m-2 s-1 and NAE of 0.2 h-1, i.e. the PM treatment. Leaf area, fresh and dry weight, and stem diameter were significantly greater in both PA and PAC treatments than those in the PM treatment, although there were no significant differences in the all growth values between both photoautotrophic treatments. Moreover, the photoautotrophic plantlets showed higher net photosynthetic rate, greater chlorophyll content, normal stomata and less microbial contamination, compared to those of the photomixotrophic plantlets. The PM plantlets had widely opened stomata with circular shape in the photo- and dark periods. The daily CO2 exchange rate (CER) was negative in the PM treatment, and positive in the PA and PAC treatments, but there was no significant difference in the daily CER between the PA and PAC treatments. The ratio of daily CER in the photoperiod was 16% in the PA without CO2 enrichment, and 27% in the PAC with CO2 enrichment. Thus, D. candidum should be considered as a facultative CAM plant. The photosynthetic pathway could change between CAM and C3 with variation of environmental factors.
Key words: CAM plant, Dendrobium candidum, functional stomata, photosynthetic pathway, sugar-free medium