Abstract
Floral induction (FI) in shoot apical meristems (SAM) is assumed to be triggered by antagonistic endogenous signals. In fruit trees, FI occurs in some SAM only and is determined by activating and inhibiting signals originating from leaves and fruit, respectively. We developed a model (SigFlow) to quantify on 3D structures the combined impact of such signals and distances at which they act on SAM. Signal transport was simulated considering a signal ‘attenuation’ parameter, whereas SAM fate was determined by probability functions depending on signal quantities. Model behaviour was assessed on simple structures before being calibrated and validated on a unique experimental dataset of 3D digitized apple trees with contrasted crop loads and subjected to leaf and fruit removal at different scales of tree organization. Model parameter estimations and comparisons of two signal combination functions led us to formulate new assumptions on the mechanisms involved: (i) the activating signal could be transported at shorter distances than the inhibiting one (roughly 50 cm vs 1 m) (ii) both signals jointly act to determine FI with SAM being more sensitive to inhibiting signal than activating one. Finally, the genericity of the model is promising to further understand the physiological and architectural determinisms of FI in plants.
Highlights
Floral induction (FI) in shoot apical meristems (SAM) is assumed to be triggered by antagonistic endogenous signals
The ‘attenuation’ parameter of the inhibiting signal (r−) was varied on a simple structure composed of six shoots located at an equal distance from each other (15 cm) and with three sources (Fig. 2a)
When no signal ‘attenuation’ (r− = 0) was considered, inhibiting signal was transported to the six SAMs (Fig. 2b): each one had an inhibiting signal value equal to 0.5 which represented the number of fruits divided by the SAM number
Summary
Floral induction (FI) in shoot apical meristems (SAM) is assumed to be triggered by antagonistic endogenous signals. Other studies[13], the existence of signal transport in both acropetal and basipetal directions within the tree was suggested This previous study[10] provided a strong experimental background from which it could be possible to infer and quantify the respective effect of inhibiting and activating signals in the within tree variability in FI, as well as their combined effects and the distance at which the emitting organs can act. In the current case of analysis of the within-tree variability in FI, functional structural plant models appear highly relevant[15] They can combine an explicit description of plant architecture (topology and organ geometry) together with the simulation of transport of different types of molecules (water, carbon, hormones, etc.).
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