Figure 1.

Suc stimulates the auxin pathway. A, Hypocotyl elongation rates of seedlings exposed to the growth-promoting hormones brassinosteroid (BR), auxin (Aux), and gibberellin (GA). Smoothed average growth rates from three independent experiments (representing an average of 15–20 seedlings per experiment) are shown. The dashed black line indicates growth rates on medium without hormone supplementation (mock). Light and dark phases are indicated in the bars below the graphs, beginning with midnight of the 3rd dpg. Bar = 0.05 mm h⁻¹. B, Suc (S), natural auxin (IAA [I]), and synthetic auxin (picloram [P]) prolonged hypocotyl elongation when compared with seedlings grown without any treatments (N). Error bars represent se. Some error bars are within the boundaries of the markers. C, Seedlings carrying the PKS4::GUS reporter showed similar GUS expression in the elongating region of the hypocotyl for Suc- and auxin-treated seedlings. Bar = 1 mm. D, Seedlings grown on Suc showed an increased sensitivity to picloram (Pic). Error bars represent se. Some error bars are within the boundaries of the markers. E, Root tips of plants grown on Suc had a reduction in fluorescence of the auxin-degradable DII-VENUS reporter. Representative images are shown with fluorescence quantification values normalized to the no-Suc mean ± se for 25 seedlings. F, Quantitative reverse transcription-PCR shows that Suc increases the expression of several auxin-induced genes. Suc effects on gene expression are much stronger in shoots (S) compared with roots (R). Error bars represent se. G, Suc (S) increased endogenous auxin levels when compared with plants grown without added Suc (N) in whole seedlings (W), hypocotyls (H), and roots (R). Error bars represent se. Asterisks indicate significant differences between Suc and no-Suc treatments for both genotypes (*P < 0.05, **P < 0.01) using Student’s t test and a Hommel multiple comparison correction. FW, Fresh weight. [See online article for color version of this figure.]