台灣蝴蝶蘭瓶苗內二氧化碳與乙烯濃度及有機酸含量之日韻律變化

Diurnal Rhythm of Carbon Dioxide, Ethylene and Organic Acid Concentration in Phalaenopsis amabilis var. formosa Plantlets in vitro

為探討台灣蝴蝶蘭（Phalaenopsis amabilis var. formosa）在瓶內之光合作用及出瓶適期，將播種後剛移至子瓶即第二次繼代（2nd subculture）階段的瓶苗進行瓶內CO2與乙烯濃度之分析，並利用瓶內CO2濃度的變化估算瓶苗之相對呼吸作用與光合作用速率，及瓶苗於光期與暗期結束前葉片有機酸的含量。結果顯示瓶內CO2與乙烯濃度均具有日韻律變化的現象，瓶內CO2濃度於繼代後第86天以前於光期開始後的4小時急遽下降，之後逐漸趨於穩定，待至暗期開始後又逐漸上升。瓶內CO2濃度會隨株齡增加而逐漸下降，繼代後第10-54天瓶內CO2濃度為2700-11500µLL^(-1)；繼代後第70-86天為1500-9000µLL^(-1)；繼代後第100-116天為0-3000μLL^(-1)，瓶苗於光期與暗期均有吸收CO2的現象，於光期結束時已降至大氣350-400μLL^(-1)以下，至暗期後2-4小時CO2已近零。瓶內乙烯濃度有隨株齡增加而上升的趨勢，暗期的乙烯濃度較高，最高達115nLL^(-1)，光期約在0-80nLL^(-1)。瓶苗株齡小者其相對呼吸與光合速率均較高，至繼代後第100天時二者均下降，且瓶苗於暗期後的4小時具吸收CO2能力。瓶苗葉片暗期有有機酸的累積，且隨株齡增加而增加，顯示瓶苗具C3和CAM（Crassulacean acid metabolism）植物之光合特性，幼苗C3路徑較強，到繼代100天葉長達5cm以上時，CAM特性增強到暗期可吸收CO2。故建議於繼代培養4個月左右就應出瓶，有利蘭株生育。

Diurnal rhythm of CO2, ethylene and organic acid concentration in Phalaenopsis amabilis var. Formosa (TS97) plants in vitro were studied. The result showed that CO2 concentration was 2700-11500μLL^(-1),1500-9000μLL^(-1) and 0-3000μLL^(-1) at 10-54 days, 70-86 days and 100-116 days after 2nd subculture (plant size at 2-2.5cm leaf length from beginning) in flask, respectively. The CO2 concentration decreased rapidly in 4 hours after the beginning of light period and increased gradually during dark period before 86 days after subculture. However, the CO2 concentration at the end of light period decreased below to the ambient concentration 350-400μLL^(-1), then decreased to zero at 2-4 hours after dark period in 100-116 days after subculture. The ethylene concentration in flask increased with increasing plant age. Ethylene concentration was higher in dark period (max.115nLL^(-1)) than light period (max.80nLL^(-1)). However, the maximum concentration never exceeded 120nLL^(-1), which was not high compared with other plantlets. The estimated relative net photosynthetic rate and estimated relative respiration rate in plantlets in vitro were the highest at 4 hours after the beginning of light period or 4 hours after the beginning of dark period, then decreased to zero before 86 days after subculture. The titratable organic acid contents increased at the end of dark period and decreased at the end of light period in 24-100 days after subculture. These indicated that carbon fixation of Phalaenopsis amabilis var. formosa was through C3 and CAM pathways during 3 months after subculture, then dramatically shifted to CAM pathway after 100-116 days after subculture. The result suggests that the plantlet in flask must be de-flask at 4 months after subculture to avoid CO2 depletion.