Hormone interplay in the regulation far-red-responsive stem elongation in tomato 4 115 Figure 4.3. Local FR treatment on each tissue as captured with infrared camera. Figure 4.4. Stem elongation in response to different local FR applications. We treated 14-dayold tomatoes with local or global supplemental FR light. The data include measurements of (a) stem length, (b) hypocotyl length, and (c) internode 1 length. 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 were 15 plants per local treatment, and the experiment was repeated three times. 4.2.3 IAA induces mild stem elongation when applied on first internode or first true leaf Commencing our exploration of the effects of different hormones, we started with the IAA-responsive pathway, indicated by our RNAseq data (Chapter 3). IAA is known to play a role in SAS in other species, specifically by induction of IAA in leaves by FR, consequently influencing petiole and hypocotyl growth. IAA application in Arabidopsis SAS studies is commonly achieved through treatments applied to diverse leaf regions or introduced into the growth medium (Michaud et al., 2017; Pantazopoulou et al., 2017). However, considering the stem growth habit of tomato compared to Arabidopsis rosette habit, we wanted to explore and test different IAA application methods. Specifically, we investigated the use of a whole plant spray and a brushing method onto both internode 1 and leaf 1 (Figure 4.5). By carefully evaluating these application techniques, we aimed to determine the most effective approach to studying IAA’s role in tomato SAS.
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