Chapter 4 124 Figure 4.10. Stem response to different PEO-IAA concentrations. We treated the first internode of 13 dag tomatoes with different concentration PEO-IAA (or mock) in WL conditions one day prior to the start of the one week FR treatment. The data includes measurements of (a) Stem length, (b) Hypocotyl length, (c) First internode length (d) Hypocotyl diameter. (e) First internode diameter. 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. Finally, we wanted to test an inhibitor of auxin biosynthesis, 4-biphenylboronic acid (BBo). BBo is a chemical that targets YUCCA, the last step in IAA biosynthesis pathway. Bbo suppressed recombinant YUC activity in vitro and decreased endogenous IAA content (Kakei et al., 2015). We firstly used a brushing method as application: we applied Bbo on the internode 1 by brushing one day in advance of FR treatment. BBo had no significant inhibitor effects (Figure S4.7). Due to the mobility of chemicals and intake time consideration, we applied BBo (and later in this chapter PBZ and BZ) also through soil penetration (Figure 4.11). To ensure proper soil penetration, we applied the inhibitors 2 days before the FR treatment by withholding water 4 days in advance and then adding 40ml of each inhibitor solution to the individual pots. However, the BBo treatment did not have any effect when applied through this method either.
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