Hormone interplay in the regulation far-red-responsive stem elongation in tomato 4 111 Figure 4.1 Arabidopsis SAS elongation regulated by auxin, gibberellin, and brassinosteroids. Regulation scheme adapted from literature (Yang and Li, 2017; Wang et al., 2020; Liu et al., 2021). Arabi dopsis picture is from Biorender.com. 4.1.2 Pharmacological tools for studying auxin, GA, and BR In this chapter, we employed a pharmaceutical approach involving hormone and hormone transport, signaling, and biosynthesis inhibitors to unravel the impact on various hormone regulations in response to far-red treatment. This approach enables us to dissect the hormone interactions, providing valuable insights into the complex hormonal dynamics of SAS. The effects of auxin can be simulated by exogenous treatments with various auxins, especially Indole-3-Acetic Acid (hereafter IAA), the most commonly occurring natural auxin. With the use of IAA, plants can be treated to cause auxin-induced growth and allows for further insight into the role of auxin in SAS. The effects of auxin can also be inhibited in different manners, in this chapter, we used three chemicals to reduce auxin biosynthesis, transport and signaling - Naphthylphthalamic acid (hereafter NPA), 4-biphenylboronic acid (BBo) and 2-(1H-Indol-3-yl)-4-oxo-4-phenyl-butyric acid)(PEO-IAA). NPA binds to the auxin transporters which makes it prevent active
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