Hormone interplay in the regulation far-red-responsive stem elongation in tomato 4 121 0 50 100 150 0 10 20 30 40 NPA concentration(μmol/L) Internode 1 length(mm) WL Mock WL+FR Mock WL NPA WL+FR NPA 0 50 100 150 0 1 2 3 NPA concentration(μmol/L) Internode1 diameter(mm) WL Mock WL+FR Mock WL NPA WL+FR NPA (a) (b) (c) Figure 4.8. Stem responses to different NPA concentrations. We treated the first internode of 13 dag tomatoes with 25, 50, 125 μM NPA (or mock) in WL conditions one day prior to the start of the one-week FR treatment. (a) Representative images of NPA phenotypes, (b) internode 1 length, (c) internode 1 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. Regardless of the NPA concentration used (50 μM and 125 μM), NPA consistently induced significant stem elongation in the hypocotyl and internode 1 (Figures 4.8, S4.5). However, we observed different responses to FR light depending on the NPA concentration. With 50 μM NPA, the stems elongated during white light (WL) treatment and this elongation was further enhanced with FR light response. Conversely, with 125 μM NPA, internode 1 elongation occurred but was reduced when exposed to FR light. Regarding stem diameter, we had noticed that hypocotyl diameter increased with FR treatment (Chapter 2). NPA consistently leads to a substantial reduction in diameter , possibly explaining why 125 μM NPA caused a significant decrease caused plants fragility (Figure 4.8(a), S4.6).
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