Figure 1.

Gravistimulation induces the rapid accumulation of NO required for gravitropism in soybean roots. a, Kinetics of NO accumulation in Zone 1 (•) or Zone 2 (○) from horizontal roots. ▾, Vertical roots. b, Correlation between NO accumulation in Zone 1 (black bars) and gravitropic curvature (white bars). Roots were pretreated as indicated for 12 h and then placed horizontally for 12 h (50 μm cPTIO; 20 μm l-NAA and NaN₃; 30 μm PBITU and NPA; 100 μm ODQ and LY83583). On x axis: C, Control; G, gravistimulated. Values are the mean ± se for five independent experiments. Data analyzed by one-way ANOVA followed by Tukey's test. Different symbols indicate significant differences between treatments (P < 0.05). c, Gravistimulation induces asymmetric NO accumulation. Soybean roots were loaded with DAF-2DA and gravistimulated by orientating horizontally. Fluorescence intensity of dissected root tips was observed at the indicated times by confocal fluorescence microscopy. Effects of pretreatment with 20 μm NaN₃, 20 μm l-NNA, 50 μm cPTIO, and 10 μm NPA are shown. The pictures were taken after 6 h treatment. Scale bar = 1 mm. Experiments were repeated at least five times with similar results. d, Asymmetric accumulation of NO in root Zone 1. Soybean roots were gravistimulated for different times, bisected horizontally with a razor blade, and NO content assayed. ▾, Vertical roots; ○, lower half of horizontal root; •, upper half of horizontal root.