Hormone interplay in the regulation far-red-responsive stem elongation in tomato 4 133 WL Mock WL BR WL GA WL GA+BR WL+FR Mock 0 50 100 150 Stem length (mm) a b b bc c WL Mock WL BR WL GA WL GA+BR WL+FR Mock 0 10 20 30 40 50 Hypocotyl length (mm) a a a a b WL Mock WL BR WL GA WL GA+BR WL+FR Mock 0 20 40 60 Internode 1 length (mm) a b b c c WL Mock WL BR WL GA WL GA+BR WL+FR Mock 0 1 2 3 4 5 Hypocotyl diameter (mm) ns WL Mock WL BR WL GA WL GA+BR WL+FR Mock 0 1 2 3 4 5 Internode 1 diameter(mm) bc c a ab abc (a) (b) (c) (d) (e) Figure 4.18. Stem response to 100 μM BR, GA or BR+GA. We brushed the first internode of 14 -day-old tomatoes with different concentration BR (or mock) in WL or FR conditions over oneweek light treatment. Brushing was applied 3 times over one-week treatment period. Data includes measurements of (a) Stem length, (b) Hypocotyl length, (c) Internode 1 length, (d) Hypocotyl diameter, (e) Internode 1diameter. Data are presented as mean ± SEM, and different letters indicate significant differences between treatments based on ANOVA analysis with Tukey’s post hoc test (P<0.05). There are 12 biological replicates, and the experiment was repeated twice. 4.2.12 Inhibiting BR signaling abolished FR-responsive stem elongation Since brassinolide boosted stem elongation in white light, we verified if inhibition of brassinosteroids would impair supplemental FR-induced elongation. We investigated this using Brassinazole, (BZ), a triazole derivative that serves as an inhibitor of brassinosteroid biosynthesis by cytochrome P450s (Asami et al., 2000).We tested the two application methods, brushing on the internode and soil penetration. We found that the BZ application by brushing was not fully effective (Figure S4.10), while with the soil penetration method BZ completely inhibited FR-responsive stem elongation (Figure 4.11, S4.11)
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