Hormone interplay in the regulation far-red-responsive stem elongation in tomato 4 137 WL Mock WL+FR BZ+GA+IAA WL+FR PBZ+IAA+BR WL+FR Mock 0 50 100 150 Stem length (mm) a b c d WL Mock WL+FR BZ+GA+IAA WL+FR PBZ+IAA+BR WL+FR Mock 0 10 20 30 40 50 Hypocotyl length (mm) a c ab bc WL Mock WL+FR BZ+GA+IAA WL+FR PBZ+IAA+BR WL+FR Mock 0 20 40 60 Internode 1 length (mm) a b c c WL Mock WL+FR BZ+GA+IAA WL+FR PBZ+IAA+BR WL+FR Mock 0 1 2 3 4 5 Hypocotyl diameter (mm) ns WL Mock WL+FR BZ+GA+IAA WL+FR PBZ+IAA+BR WL+FR Mock 0 1 2 3 4 5 Internode 1 diameter (mm) a b a a (a) (b) (c) (d) (e) (f) Figure 4.21. Stem responses to 100 μM PBZ and BZ with the other two hormones. We drained the soil 4 days before FR treatment, and applied BBo, PBZ and BZ directly to the soil 2 days before FR treatment in FR conditions. We brushed the first internode of 14 day-old tomatoes with different concentration BR(or mock) in WL or FR conditions over one week FR treatment. Brushing was applied 3 times over one week treatment period. (a)Illustration of how to apply the soil penetration and hormone. The data includes measurements of (b) Stem length, (c) Hypocotyl length, (d) Internode 1 length, (e) Hypocotyl diameter, (f) Internode 1 diameter. The 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 8 biological replicates. Picture was created by Biorender. In conclusion, our experiments testing the interplay of BR, IAA and GA demonstrated that the both BR and GA are necessary for the FR-induced internode elongation, but either one of them can be rescued by the other one (combined with IAA in our experiments). We also saw that the effects of GA and BR might be additive, so it indicates both of them play a role in the FR-induced internode elongation. The role of IAA and how it interacts with BR and GA remains elusive, and might be complicated by internal concentrations or spatial patterns that cannot be emulated though exogenous IAA or inhibitor applications.
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