植物組織培養器内環境の基礎的研究

(3) 培養小植物体を含む閉栓容器内の炭酸ガス濃度測定と培養小植物体の純光合成速度の推定

抄録

This paper describes the CO₂ concentration in tissue culture vessels and the net photosynthetic rates of tissue cultured plantlets in the closed vessels with stopper.
Firstly, this paper shows changes with passage of time in CO₂ concentration in the closed vessels containing plantlet (s) cultured under usual conditions. Secondly, it gives the estimated net photosynthetic rates of plantlets cultured in the closed vessels. Lastly, it estimates the effects of CO₂ enrichments on the photosynthetic rate of one of the plantlets used.
The plantlets used were 8 genera of ornamental foliage, and had grown large enough to pot. The CO₂ concentration was measured by using a gas chromatograph.
In order to estimate the photosynthetic rates of the plantlets in the closed vessels, a model of CO₂-net photosynthesis was developed, and the parameters of the model were estimated on the basis of the measured values of the CO₂ concentration in the closed vessels.
The model is given by the following equation:
P_n=P_ns⋅[1-exp {-G/P_ns⋅(K_c-C)}]
where P_n is the net photosynthetic rate [μcm³ CO₂ mg^-1 h^-1], P_ns the saturated net photosynthetic rate for CO₂ concentration [μcm³ CO₂ mg^-1 h^-1], G the gradient of CO₂-net photosynthesis curve at CO₂ compensation concentration [μcm³ CO₂ mg^-1 h^-1 vpm^-1], K_c the CO₂ concentration in the closed vessel [vpm], and C the CO₂ compensation concentration [vpm]. P_ns, G and C are the parameters of this model.
The results can be summarized as follows:
(1) In all closed vessels, the CO₂ respired in the dark period was accumulated to the concentration level from about 3000 to 9000vpm. One or two hours after the start of the light period, the CO₂ concentration in the vessels are rapidly decreased to less than 90vpm by the photosynthesis of plantlets. Thus, it became clear that all plantlets have photosynthetic ability under the light period.
(2) The plantlets could not fully achieve their photosynthetic capacity, because the CO₂ concentration in the closed vessels were too low in most of the light period.
(3) Estimated net CO₂ uptake per day of all plantlets in the closed vessels were negative. This means that the plantlets had grown by using sucrose in the media as the main source of carbonhydrate.
(4) The results of the estimation on the effects of CO₂ enrichment indicate that net photo-synthetic rate of a plantlet may be increased not only by increasing the inside CO2 concentration, but also by increasing the outside concentration or by increasing the number of air changes of the vessel when the outside concentration is higher than that of inside during the light period.
The above results indicate that tissue cultured plantlets in the closed vessels can be grown photoautotrophically during and after the multiplication stage by improving the CO₂ and light environments in the closed vessels.