13C labeling and abundance analysis
The maize ear leaf was labeled with13C-CO2 at the flowering stage, as
Supporting Information Figure S2. The ear leaf was covered in a13C-CO2 labeling bag (material:
biaxially oriented polypropylene film (BOPPF); standard:
width×length×thickness = 12×120×2
cm) and injected with 100 mL 13C-CO2.
Mixed CO2 from the leaf tip to the bottom was carefully
anchored with a nylon rope to avoid breaking by external factors, e.g.,
wind. Both sides of maize plants were marked differently to avoid any
possible confusion. The tissue samples for analyses were taken after 1,
10, 20, 30, 40 days 13C labeling. The activity of13C was determined by the previously described
(Liu et al., 2015) procedure. The
abundance of 13C was established using an isotope
ratio mass spectrometer (Delta VIRMS Thermo Fisher Scientific, USA).