Exploring conservation of cellular-level traits in shade avoidance syndrome among species 5 191 Figure 5.15. Conservation patterns of homologs of Solyc08g080150. The alignment shows regions of conservation highlighted in red, illustrating >50% identity, white indicates <50% identity. 5.3 DISCUSSION 5.3.1 Shade avoidance elongation is most likely conserved but with exceptions In the preceding chapters, we explored the mechanism of stem elongation and the associated radial growth in tomato, which prompted us to try and transfer this question to be studied in Arabidopsis (Figures 5.2, 5.3). The rationale behind this transfer was rooted in the rich genetic resources already established in Arabidopsis, presenting an ideal foundation for further investigation. However, our experimentation revealed that the FR-responsive stem elongation in Arabidopsis was not experimentally robust, highlighted by the lack of the response under short-day conditions. Under long-day conditions and relatively low photosynthetically active radiation (150 PAR), we employed a very low red to far-red light ratio (R:FR) of 0.11 to elicit a response. When we tested a higher R:FR ratio of 0.25 in this setting, the elongation response vanished. Inflorescence stem elongation in response to FR in long day was observed also at 200 PAR. Integrating both sets of conditions, we hypothesize that the actual amount of far-red light and its duration of exposure play pivotal roles in inducing inflorescence stem elongation. In Arabidopsis, the radial expansion of the stem is influenced by various factors, including light quality, genetic interactions between receptor kinases, and the activity of multiple transcription factor genes (Génard et al., 2001; Greb, 2019; Spaninks et al., 2023). The stem
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