| Summary: | 博士 === 國立屏東科技大學 === 熱帶農業暨國際合作系 === 105 === Phalaenopsis is a monopodial and traditional horticultural epiphytic orchid species with high commercial value as cut flowers and potted plants. It has been successfully adapted for the mass propagation. There are many factors that effect on the growth and development of Phalaenopsis seedlings such as light quality, intensity and temperature. These effects may change the photosynthesis mechanism and growth of in vitro seedlings from C3 to CAM in Phalaenopsis. The purposes of this study were to investigate the photosynthesis mechanism change through different environment factors in Phalaenopsis in vitro seedling and the C3-CAM transformation of related species within Vanda family.
In first experiment, ways in which light quality influences plant photosynthesis, growth parameters and carbon dioxide rhythms of different sizes (stage I, II and III) of Phalaenopsis Fortune Saltzman tissue culture seedlings were examined. Stage I (seedling of 1-2 cm in height with 1-2 leaves and 1-2 roots) tissue culture seedlings were grown under six different light qualities under a T5 fluorescent lamp: White, Red (610 nm), Red (658 nm), Blue (440 nm), Red (610 nm) + Blue (440 nm) and Red (658 nm) + Blue (440 nm). After 5 months, cultured seedlings exposed to the Blue (440 nm) treatment showed significantly higher responses in terms of leaf quantities and chlorophyll a, chlorophyll b, total chlorophyll and carotenoid content. On the other hand, seedlings subjected to the Red (658 nm) treatment grew more stems and presented higher fresh weight and leaf lengths compared to the results of other treatments. The number of roots increased under the Red (658 nm), Blue (440 nm) + Red (610 nm) and Blue (440 nm) + Red (658 nm) treatments. Moreover, seedlings subjected to Red light (658 nm) showed significantly higher levels of Rubisco enzyme activity than those subjected to the other treatments. Phosphoenolpyruvate carboxylase activities recorded during the nighttime in seedlings subjected to Red light (658 nm) were also significant greater. The CO2 rhythm results showed that during stage I, the concentration of carbon dioxide rhythm ranged from 1,500-1,800 ppm and reflected a C3 photosynthesis system. As the seedlings matured, the carbon dioxide decreased to 400-800 ppm at night and reached stage III (CAM plant). After 5 months of culture, the carbon dioxide rhythm of the Red (658 nm) treatment seedlings changed from C3 to CAM while seedlings subjected to the other treatments still occupied the intermediate stage (stage II). From these results, we conclude that to enhance seedling growth through commercial production, Red (658 nm) should be applied.
The effects of different light intensities (17.86, 32.14, 35.71 and 53.57 μmolm-2s-1) were examined. After 5 months of culture, seedlings subjected to the 35.71 μmol m-2 s-1 treatment showed significantly longer root and leaves and higher number of root and leaves than those subjected to the other treatments. The seedlings grown under 35.71 μmol m-2 s-1 light conditions showed significantly higher levels of chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, sugar and starch content than those grown under other treatments. The seedlings under 32.14 μmol m-2 s-1 treatment showed significantly highest nitrogen contents level of all of the seedlings studied. In terms of photosynthetic enzyme activities, after 5 month of culture, the control treatment showed significantly higher levels of Rubisco activity during the day while, 35.71 μmol m-2 s-1 treatment showed significantly higher levels of Rubisco activity during the night. After 7 months of culture, seedlings subjected to the 35.71 μmol m-2 s-1 treatment showed significantly higher fresh and dry weight and longer root and leave values than other treatments. The seedlings grown under 35.71 μmol m-2 s-1 light conditions showed significantly higher levels of chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, sugar and starch content than those grown under other treatments. The seedlings under 32.14 μmol m-2 s-1 treatment showed significantly highest nitrogen contents level of all of the seedlings studied. In terms of photosynthetic enzyme activities, after 7 month of culture, the 35.71 μmol m-2 s-1 condition showed significantly higher levels of Rubisco and PEPC activities during the day and night. From these results, we concluded that higher light intensity can enhance seedling growth and physiological transformation from C3 to CAM, for commercial production, 35.71 μmol m-2 s-1 should be applied.
In third experiment, Phalaenopsis Fortune Saltzman tissue culture seedlings were grown under 5 different day/night temperature (25/25 ºC, 25/20 ºC, 30/20 ºC, 30/25 ºC, 35/25 ºC). The seedlings from stage I were used to proceed their growth and evaluation. It exhibited two discrete CO2 absorption periods, and more C3 to CAM carbon fixation pattern were found. After 7 months of cultured, seedlings showed significantly decreased CO2 concentration at night, and showed a typical CAM plant carbon fixation pattern. The result showed that after 7 months of cultured, 30/20 ºC and 30/25 ºC treatments grew more stems and presented higher fresh weight and leaf lengths compared to the results of other treatments. Moreover, 30/25 ºC treatment showed significantly higher responses in terms of dry weight, number of root, root length and number of leaf. The seedlings subjected to 30/25 ºC treatment showed significantly higher levels of Rubisco enzyme activity than those subjected to the other treatments. PEPC activities recorded during the nighttime in seedlings subjected to 30/25 ºC were also significant greater. Therefore, 30/25 ºC treatment could advance growth of Phalaenopsis Fortune Saltzman tissue culture seedlings faster and can be recommended for commercial production of Phalaenopsis industry.
The purpose of fourth experiment was to study the relationship of Phalaenopsis related species in photosynthetic mechanism and morphology traits. The results showed that the Vanda genus species seedlings used can be clearly indentified into three photosynthesis stages through CO2 rhythm detecting. After 1 months of culture all seedling showed greater Rubisco enzyme activity at day than during the night, serving as evidence of a C3 photosynthesis system. After 5 months of culturing, most seedlings showed greater PEPC enzyme activity at night than during the day as evidence of a CAM photosynthesis system. But, different species showed various CO2 concentration and different CO2 rhythm patterns. It showed evidence of physiological pattern transformations from C3 to CAM during the growth period. After 7 months, they all performed as CAM plant. While compare to a Cymbidium species tested, it remained as a C3 pattern throughout the entire experimental period. Thus, this experiment also confirm the thick leaf Vanda orchid species follow the same physiological transformation pattern as Phalaenopsis in vitro. In conclusion, the C3-CAM photosynthesis transformation existed in thick leaf Vanda species and suitable environmental factors such as light quality (Red 658), light intensity (35.72 μmol m-2 s-1) and temperature (30/25 ºC) can shorten its transformation which exist high potential for both species conservation and commercial products.
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