RESUMEN

In polycarpic plants, meristem fate varies within individuals in a given year. In perennials, the proportion of floral induction (FI) in meristems also varies between consecutive years and among genotypes of a given species. Previous studies have suggested that FI of meristems could be determined by the within-plant competition for carbohydrates and by hormone signaling as key components of the flowering pathway. At the genotypic level, variability in FI was also associated with variability in architectural traits. However, the part of genotype-dependent variability in FI that can be explained by either tree architecture or tree physiology is still not fully understood. This study aimed at deciphering the respective effect of architectural and physiological traits on FI variability within apple trees by comparing six genotypes with contrasted architectures. Shoot type demography as well as the flowering and fruit production patterns were followed over 6 years and characterized by different indexes. Architectural morphotypes were then defined based on architectural traits using a clustering approach. For two successive years, non-structural starch content in leaf, stem and meristems, and hormonal contents (gibberellins, cytokinins, auxin and abscisic acid) in meristems were quantified and correlated to FI within-tree proportions. Based on a multi-step regression analysis, cytokinins and gibberellins content in meristem, starch content in leaves and the proportion of long shoots in tree annual growth were shown to contribute to FI. Although the predictive linear model of FI was common to all genotypes, each of the explicative variables had a different weight in FI determination, depending on the genotype. Our results therefore suggest both a common determination model and a genotype-specific architectural and physiological profile linked to its flowering behavior.

Asunto(s)

Malus , Malus/metabolismo , Giberelinas/metabolismo , Citocininas/metabolismo , Árboles , Genotipo , Almidón/metabolismo , Flores

RESUMEN

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.

Asunto(s)

Malus/citología , Malus/metabolismo , Modelos Biológicos , Transducción de Señal , Transporte Biológico , Malus/crecimiento & desarrollo , Meristema/crecimiento & desarrollo

RESUMEN

In plants, organs are inter-dependent for growth and development. Here, we aimed to investigate the distance at which interaction between organs operates and the relative contribution of within-tree variation in carbohydrate and hormonal contents on floral induction and fruit growth, in a fruit tree case study. Manipulations of leaf and fruit numbers were performed in two years on "Golden delicious" apple trees, at the shoot or branch scale or one side of Y-shape trees. For each treatment, floral induction proportion and mean fruit weight were recorded. Gibberellins content in shoot apical meristems, photosynthesis, and non-structural carbohydrate concentrations in organs were measured. Floral induction was promoted by leaf presence and fruit absence but was not associated with non-structural content in meristems. This suggests a combined action of promoting and inhibiting signals originating from leaves and fruit, and involving gibberellins. Nevertheless, these signals act at short distance only since leaf or fruit presence at long distances had no effect on floral induction. Conversely, fruit growth was affected by leaf presence even at long distances when sink demands were imbalanced within the tree, suggesting long distance transport of carbohydrates. We thus clarified the inter-dependence and distance effect among organs, therefore their degree of autonomy that appeared dependent on the process considered, floral induction or fruit growth.