Higher growth of the apple (Malus \xd7 domestica Borkh.) fruit cortex is supported by resource intensive metabolism during early development

Shan Jing,Anish Malladi

doi:10.1186/s12870-020-2280-2

Abstract

BackgroundThe major fleshy tissues of the apple fruit are spatially separable into cortex and pith. These tissues display differential growth during development. Key features of such differential growth, and sink metabolic programs supporting it have not been investigated previously. We hypothesized that differential growth between these fruit tissues is supported by differential sink metabolic programs, particularly during early development. Growth, metabolite concentrations, and transcript abundance of metabolism-related genes were measured to determine characteristics of differential growth and their underlying metabolic programs.ResultsThe cortex displayed > 5-fold higher growth than the pith during early fruit development, indicating that differential growth was established during this period. Further, when resource availability was increased through sink-removal, cortex growth was preferentially enhanced. Greatest diversity in metabolic programs between these tissues was evident during early fruit development. Higher cortex growth during early development was facilitated by increased catabolism of imported carbon (C) resources, sorbitol and sucrose, and the nitrogen (N) resource, asparagine. It was also associated with enhanced primary C metabolism, and C storage as malate and quinate. The pith metabolic program during this period involved limited allocation of C and N to growth, but greater allocation to storage, and enhanced sucrose-sucrose cycling.ConclusionsTogether, these data indicate that the fruit cortex tissue displays a resource intensive metabolic program during early fruit development. This provides the C backbones, proteins, energy and osmolytes to support its higher growth.

Highlights

The major fleshy tissues of the apple fruit are spatially separable into cortex and pith
Preferential growth of fruit cortex Fruit growth was enhanced by the fruit load reduction treatment performed at 11 Days after full bloom (DAFB) [(Figs. 1b-d; 11 DAFB = 0 d after treatment (DAT)]
Fruit in the reduced fruit load (RL) treatment displayed greater diameter (9.4%; P < 0.01) by 19 Days after treatment (DAT), which continued until 118 DAT

Summary

Introduction

The major fleshy tissues of the apple fruit are spatially separable into cortex and pith. These tissues display differential growth during development. We hypothesized that differential growth between these fruit tissues is supported by differential sink metabolic programs, during early development. The apple fruit has two major fleshy tissues: cortex and pith (Fig. 1a). The receptacular hypothesis posits that the fruit fleshy tissues are of axial origin extending from the pedicel and receptacle. The appendicular hypothesis posits that the cortex which constitutes the largest portion of the fruit at maturity, is derived from accessory tissue, likely from the fused basal regions of sepals, petals and anthers [1, 2].

Methods

Results

Conclusion