General introduction 21 1 pea (Pisum sativum), exposure to low R:FR conditions has been shown to increase the production of strigolactones, which in turn promote the growth of lateral roots and suppress shoot branching (Dun et al., 2013). In rice, strigolactone has been proven to promote tiller architecture (Zha et al., 2022). 1.3 STEM GROWTH 1.3.1 Comparison of stem and petiole The stem is a support and transport organ in vascular plants. Plant stems have nodes from which they grow leaves, aerial roots, and flowers, and the sections of stem between nodes are called internodes. The conjunctive tissue that extends from the stem to the leaf lamina is the petiole (Mauseth, 2003). Petioles are generated from leaf primordium, and petiole activities are regulated by hormones and light (Sasidharan et al., 2010; Pierik and De Wit, 2014; Bravo et al., 2016). Both petioles and stem show elongation in SAS. Regarding their cellular morphology (Figure 1.6), both of them have epidermis, parenchyma and vascular bundles, and the vascular bundles in the petiole usually show multiple shapes, different from the mostly circular shape in stems (Ergen Akçin et al., 2011; Ragheb et al., 2019). Figure 1.6. Petiole and inflorescence stem cross sections of Arabidopsis. (a) Cross section of the petiole, provided by Sanne Matton. (b) Cross section of the inflorescence stem. 1.3.2 Primary growth and secondary growth Plant growth is categorized into primary growth, which increases the length or height of the plant, and secondary growth, which augments the plant’s diameter. Secondary growth is facilitated by lateral meristems, specifically the vascular cambium and cork cambium (Etchells and Turner, 2010). The cork cambium forms the outer ring of the stem, giving
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