Impact of Within-Tree Organ Distances on Floral Induction and Fruit Growth in Apple Tree: Implication of Carbohydrate and Gibberellin Organ Contents

Abstract

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.

Modelling transport of inhibiting and activating signals and their combined effects on floral induction: application to apple tree

“…The model proved its ability to represent experimental observations in which the within-tree distribution of www.nature.com/scientificreports/ inhibiting and activating sources were artificially modified 10 . It was also able to rebuild the relationship between tree crop load and the proportion of flowering SAMs in the next year 35 .…”

“…'Golden Delicious') orchard, located at the SudExpé experimental station in Marsillargues, in the south of France (43° 66′ N 4° 18′ E). In this experiment described in Belhassine et al 10 , leaves and/or fruit were removed in different parts of the tree ( Supplementary Fig. S2).…”

“…This assumption is consistent with the differential expressions of genes involved in carbon metabolism between meristems of apple trees subjected to defruited or fruited conditions 9 . Nevertheless, experimental findings have proved that the tree carbon economy is not directly involved in FI control in apple 10 . Another assumption, based on seedless varieties, considers that FI is probably affected by inhibiting signals produced by seeds of fruit, mainly gibberellins 11 (GA).…”

“…In a previous study 10 the impact of leaf and fruit presence on within-tree FI variability was investigated in 'Golden Delicious' cv. Results confirmed the existence of promoting and inhibiting signals, originating from leaves and fruit respectively.…”

A Comparative Study on the Branching Pattern of Monocyclic and Bicyclic Shoots of Apple cv. “Fuji”

“…In addition, fruit load also plays a key role in floral induction. Indeed, under high crop load condition, inhibiting signal coming from fruits restrains floral induction ( Dennis and Neilsen, 1999 ; Belhassine et al, 2019 ).…”