The release of oxygen gas from rice roots was measured
by methylene blue method. The oxidized methylene blue
was blue and the reduced one is colorless (Shiono et al.
2011). First, 1.0 g of agar was dissolved in 1 L of distilled
water and boiled in microwave oven. After cooling,
13 mg of methylene blue was added into the agar solution,
and the solution turned blue since it existed as
oxidative status. Then 0.13 g of sodium dithionite was
added into the solution, and the solution turned colorless.
The measurement was conducted in a transparent glass
box (300 mm 9 40 mm 9 300 mm) containing dye
solution. A rice seedling was placed into dye solution
with the root posterior at 50 mm below the surface, and
the rest of the shoot was kept in air. After 30-min culture
in dark at 28 C, the roots in agar solution were
photographed.