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Axillary bud outgrowth regulation by light intensity: Modelling hormone and sugar interactions

Bertheloot J., Schneider A., Ledroit L., Perez-Garcia M.D., Boudon F., Godin C., Sakr S.. 2020. In : Kahlen Katrin (ed.), Chen Tsu-Wei (ed.), Fricke Andreas (ed.), Stützel Hartmut (ed.). Book of abstracts of the 9th International Conference on Functional-Structural Plant Models: FSPM2020, 5 - 9 October 2020. Hanovre : Institute of Horticultural Production Systems, p. 78-79. International Conference on Functional-Structural Plant Models (FSPM 2020). 9, 2020-10-05/2020-10-09, (Allemagne).

Introduction - Branching is a key trait of plant adaptation to growth conditions. It involves a regulation of the outgrowth of axillary buds. These are inhibited by the fast-growing apical zone, a phenomenon called apical dominance. The extent of this inhibition depends on plant growth conditions. In this work, we investigate the ability of light intensity to modulate apical dominance and seek to identify the underlying mechanisms. Apical dominance is mediated by hormonal and sugar competition mechanisms (Rameau et al., 2015; Schneider et al., 2019). The fast-growing apical zone is, on the one hand, a source of auxin, that is transported downwards in the stem and indirectly inhibits bud outgrowth. Auxin rapidly controls the production of two other hormones, the cytokinins (CK) and strigolactones (SL) in bud neighborhood, that are the direct regulators of bud outgrowth. On the other hand, the fast-growing apical zone is a highly important sink organ that deprives axillary buds from sugar (Mason et al. 2014). Such deprivation inhibits bud outgrowth in an unknown manner (Barbier et al., 2015). Plant incident light intensity dampened apical dominance through increasing CK production in the stem in rose (Corot et al., 2017). The sugar involvement in light effect is unclear, despite light-induced changes in photosynthesis and plant sugar level. Here, we hypothesize that both CK and sugar are involved in incident light-related stimulation of bud outgrowth and antagonize dose-dependently auxin inhibiting effect. Moreover, CK production is supposed to be related to light perceived locally by the bud-bearing stem. Our objective was to test, by a combination of experiments and simulations, whether this hypothesis accounts for bud outgrowth differences observed between three light intensity regimes experienced by rose plants. First, we developed and calibrated a model at the scale of the bud-bearing stem using experiments in vitro. It assumes an effect of light on CK production

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