| Preparation |
Nonlabeled onion bulbs (sections) were purchased from SI Science (Japan). Onion plants were grown under 12CO2 (1.1 atom % 13C) in a growth chamber. The plants were grown for 12 weeks under controlled conditions: day/night cycle, 14/10 h; temperature, 23/15 C (day/night); relative humidity, 75%/85% (day/night); light, 600 umol/m2; and hydroponics nutrient solution, Hoagland type. After cutting 12-week-old bulbs into 1-cm squares, the samples were immediately frozen with liquid nitrogen and lyophilized at -55 C. The lyophilized materials were stored at room temperature with silica gel. |