Chapter 2 48 Overall, this chapter explored the relationship between primary and secondary plant growth, with a focus on interfascicular cambium’s connection with stem elongation. While FR treatment led to increased interfascicular cambium thickness, indicating active proliferation, it didn’t significantly affect xylem development. This aligns with prior research showing that dark conditions, which similarly are signalled through phytochromes and PIFs, can hinder vascular differentiation, highlighting the interplay between light and xylem differentiation in plant growth. We also highlighted the need for a deeper understanding of the connection between secondary growth and pith with stem elongation. 2.3.4 Summary In our investigation of tomato, we observed a SAS phenotype consistent with expectations, although prior studies on tomato SAS are limited. We further explored the relationship between primary and secondary plant growth, including pith cell elongation and interfascicular cambium in stem elongation. This chapter highlights the intricate relationship between primary and secondary growth in tomato response to supplemental far-red light, emphasizing the need for further research to understand the dynamics in SAS. 2.4 MATERIAL AND METHODS 2.4.1 Light treatments Plants were grown in long day conditions (8 h of darkness and 16 h of light) under natural spectrum of 190-200 μmol m–2 s–1 photosynthetically active radiation (PAR), far-red spectrum of 0 µmol and a R/FR ratio of 2,000. They were grown with white light HPI lamps with a temperature of 25°C at day and 20°C at night, with humidity of 70%. To simulate canopy shade, FR LEDs (730nm, Philips GreenPower) were used to apply supplemental FR light and to change R:FR ratio to 0.3 (Figure 2.20). For experiment of epidermis imprint, vascular bundle structure quantification, and R/ FR ratio test, plants were grown in light condition shown in Figure 2.21. Majority of the experiment was carried out with R:FR ratio 0.2, and a few experiments were conducted with R:FR=0.11.
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