placed vertically in rows, after recording the initial positions of
the root tips, the plates were rotated by 90° and placed vertically
for gravistimulation under different concentrations of
NH4
+ (0, 10, 20 and 30 mM (NH4)2SO4) in a cultivation
chamber at time zero. Digital images of seedling growth were
captured at regular, specified time points (as defined in the
text) following gravistimulation with a Canon G7 (Canon Inc.,
Tokyo, Japan). The root elongation and tip angles from the
vertical were determined as described by Sun et al. (2008).
Root elongation refers to the length of the primary root after
transfer to treatment solution, whereas the gravitropic angle
refers to the angle of the root tip relative to the gravity vector.