Understanding shoot branching by modelling form and function (original) (raw)
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Multiple pathways regulate shoot branching
Frontiers in Plant Science, 2015
Shoot branching patterns result from the spatio-temporal regulation of axillary bud outgrowth. Numerous endogenous, developmental and environmental factors are integrated at the bud and plant levels to determine numbers of growing shoots. Multiple pathways that converge to common integrators are most probably involved. We propose several pathways involving not only the classical hormones auxin, cytokinins and strigolactones, but also other signals with a strong influence on shoot branching such as gibberellins, sugars or molecular actors of plant phase transition. We also deal with recent findings about the molecular mechanisms and the pathway involved in the response to shade as an example of an environmental signal controlling branching. We propose the TEOSINTE BRANCHED1, CYCLOIDEA, PCF transcription factor TB1/BRC1 and the polar auxin transport stream in the stem as possible integrators of these pathways. We finally discuss how modeling can help to represent this highly dynamic system by articulating knowledges and hypothesis and calculating the phenotype properties they imply.
Modeling of Branching Patterns in Plants
Bulletin of Mathematical Biology, 2008
A major determinant of plant architecture is the arrangement of branches around the stem, known as phyllotaxis. However, the specific form of branching conditions is not known. Here we discuss this question and suggest a branching model which seems to be in agreement with biological observations.
Patterns of external branching link form and function across diverse plants
The West, Brown, Enquist (WBE) model derives symmetrically self-similar branching to predict metabolic scaling from hydraulic conductance, K, (a metabolism proxy) and tree mass (or volume, V). The original prediction was K / V 0:75 . We ask whether trees differ from WBE symmetry and if it matters for plant function and scaling. We measure tree branching and model how architecture influences K, V, mechanical stability, light interception and metabolic scaling.
Oecologia, 1997
Shade-induced changes in the branching pattern of clonal plants can lead to conspicuous modifications of their growth form and architecture. It has been hypothesized that reduced branching in shade may be an adaptive trait, enabling clonal plants to escape from unfavourable patches in a heterogeneous environment by allocating resources preferentially to the growth of the main axis (i.e. linear expansion), rather than to local proliferation by branching. However, such an adaptionist interpretation may be unjustified if (1) branching frequency is a function of the ontogenetic stage of plants, and if (2) shading slows down the ontogenetic development of plants, thereby delaying branch formation. In this case, architectural differences between sun- and shade-grown individuals, harvested at the same chronological age, may not represent a functional response to changes in light conditions, but may be a by-product of effects of shade on the rate of plant development. To distinguish between these two alternatives, individuals of the stoloniferous herb Potentilla reptans were subjected to three experimental light conditions: a control treatment providing full daylight, and two shade treatments: neutral shade (13% of ambient PPFD; no changes in light spectral composition) and simulated canopy shade (13% PPFD and a reduced red:far-red ratio). Plant development was followed throughout the experiment by daily monitoring primary stolon growth as well as branch and leaf initiation. Biomass and clonal offspring production were measured when plants were harvested. At the end of the experiment shaded plants had produced significantly fewer branches than clones grown in full daylight. In all three treatments, however, initiation of secondary stolons occurred at the same developmental stage of individual ramets. Shading significantly slowed down the ontogenetic development of plants and this resulted in the observed differences in branching patterns between sun- and shade-grown individuals, when compared at the same chronological age. These results hence provide evidence that shade-induced changes in the branching pattern of clonal plants can be due to purely allometric effects. Implications for interpreting architectural changes in terms of functional shade-avoidance responses are discussed.
Sprouting by plants: the effects of modular organization
Functional Ecology, 2004
1. Plant survival following disturbance was modelled simply as the probability that at least one of n stems sprouts, each stem having an independent probability of sprouting, s . This first-order model with any stem on any plant in any species having probability s = 0·18 of sprouting after clipping ( s = 0·09 after burning) explained nearly half of the deviance associated with species' mortality in a field experiment on 43 species from a range of growth forms. 2. Allowing species to take either a low or high per-stem sprouting probability (SSP) improved statistical explanation substantially. Fitting growth form SSP was less effective, showing that much of the apparent among-species variation in SSP was within growth forms. 3. Allowing each species to have a different SSP essentially provided a saturated model. The estimated species-specific probabilities were positively related to the depth from which sprouts could emerge after disturbance. Predicting species' bud depth from some simply measured morphological trait would be a considerable advance. Limited evidence suggested that sprout depth was associated with thick or dense leaves (low specific leaf area and leaf water content). 4. Depicting plants as a collection of independent stems with equal probability of sprouting appears a reasonable first-order model for whole-plant sprouting, despite being morphologically simplified.
Plant science modeling branching in cereals
2013
The primary adaptive response is a variable degree of branching, called tillering in cereals. Especially for heterogeneous plant configurations the degree of tillering varies per plant. Functional-structural plant modeling (FSPM) is a modeling approach allowing simulation of the architectural development of individual plants, culminating in the emergent behavior at the canopy level. This paper introduces the principles of modeling tillering in FSPM, using (I) a probability approach, forcing the dynamics of tillering to correspond to measured probabilities. Such models are particularly suitable to evaluate the effect structural variables on system performance. (II) Dose-response curves, representing a measured or assumed response of tillering to an environmental cue. (III) Mechanistic approaches to tillering including control by carbohydrates, hormones, and nutrients.Tiller senescence is equally important for the structural development of cereals as tiller appearance. Little study has been made of tiller senescence, though similar concepts seem to apply as for tiller appearance.
Grass architecture: genetic and environmental control of branching
Current Opinion in Plant Biology, 2007
Variation in grass architecture profoundly affects light capture, competition, and reproductive success, and is responsive to environmental factors such as crowding and nutrient limitation. Recent work in both model and crop systems has uncovered many aspects of the genetic control of branching, including conservation of the MONOCULM1 and MORE AXILLARY BRANCHING/DECREASED APICAL DOMINANCE/RAMOSUS (MAX/DAD/RMS) genetic pathways among the grasses and the model dicot systems of tomato, Arabidopsis, Petunia and pea. Parallel studies on the effect of environment on branching have also begun to uncover links between environmental sensing through phytochrome pathways, and resultant changes in TEOSINTE BRANCHED1 expression, and meristem inhibition. Future work promises to integrate knowledge of phenotypic responses to environment with our understanding of the genetic and hormonal changes that underlie phenotypic change.