314 mm, as shown in Fig. 5. Both ends of the silicon tube were
connected with a waterproof tape, and 10 holes of about 3 mm in
diameter were placed on the same plane of the silicon tube for
transplanting. This original device was able to reduce the area of
the air–liquid interface by 98% and the quantity of liquid medium
required by 70% compared with an 85-mm-long, 45-mm-wide and
30-mm-high flat holder.
Arabidopsis thaliana was used as the test plant. Individual plants,
which had been incubated in the dark at 4 ◦C for 2 days to break
dormancy and grown for 10 days in a commercial growth chamber,
were used in the experiments. The plants were grown on
1/2 Murashige–Skoog (MS) media containing 1.5% (w/v) sucrose
and 0.7% (w/w) agar from sowing to transplanting. The temperature
in the commercial plant growth chamber was maintained
at about 23 ◦C with a photoperiod of 16 h/8 h light/dark cycle. The
photon flux density (PFD) in the commercial growth chamber was
about 40 mol/m2s. To reduce interplant variability, 10 plants were
selected from approximately 40 plants. The original support device,
on which 10 plants were transplanted and which contained 8.8 mL
of 1000 times diluted Hyponex (10 N – 3P – 3 K – 0.05 Mg – 0.001 Mn
– 0.005B, HYPONeX Japan, Co. Ltd.) liquid medium, was set at the
bottom of the chamber. Before starting the experiment, the gas in
the chamber was replaced by compressed air from a gas cylinder for
5 min. Then, the pressure in the chamber was set at 0.1 MPa, and the
plants were incubated for 3 h under 0.1 MPa. The gas in the chamber
was sampled and the CO2 concentration was analyzed before
and after incubation. Then, the gas in the chamber was replaced
with the gas supplied from a gas cylinder for 5 min before changing
the pressure. Next, the same plants were incubated for 3 h in the
pressure range from 0.1 to 0.5 MPa. Then, the gas in the chamber
was sampled and analyzed by micro gas chromatography (CP4900,
VARIAN). The photon flux density (PFD) in the chamber was about
40 mol/m2s in the light condition to analyze the rates of photosynthesis.
The rates of respiration were analyzed in the dark. The
rate of decrease or increase in the amount of CO2 in the chamber
for 3 h was regarded as the rate of photosynthesis or respiration,
respectively. PFD was measured using a light meter (Licor, Li-250A).