Metabolomics Analysis of Litchi Leaves during Floral Induction Reveals Metabolic Improvement by Stem Girdling.

Zuanxian Su,Wenjie Huang,Qiushen Xiao,Jiyuan Shen,Shijuan Yan,Houbin Chen

doi:10.3390/molecules26134048

Abstract

Prolonged exposure to cold temperatures often results in a relatively low flowering rate in litchi (Litchi chinensis Sonn.) trees with younger leaves. This study aimed to verify the impact of stem girdling on litchi flowering by identifying and characterizing the induced metabolic changes. After a 60 day exposure to cold treatment at 15 °C/10 °C (12 h/12 h), the flowering rate of the girdled trees was 100%, while that of the non-girdled trees was 20%, indicating that girdling improved litchi flowering at its turning stage. The metabolic profiles of litchi leaves with and without stem girdling during floral induction were compared and 505 metabolites potentially associated with litchi flowering were detected. Most metabolites were involved in the metabolism of starch and sucrose, fatty acid, and phenylpyruvic acid. The metabolic pathways concerned with the biosynthesis of epinephrine, sucrose, and d-maltose were induced in leaves after girdling treatment. The level of galactitol, phenylpyruvic acid, acetyl-CoA, linoleic acid, alpha-linolenic acid, and 13-HPOT biosynthesis remained stable in the leaves from girdled trees but changed drastically in the leaves from non-girdled trees. In addition, 379 metabolites concerning flowering rate were characterized. Metabolism pathways of starch and sucrose, galactose, and linoleic acid are of great significance to the flowering of litchi. Linoleic acid exhibited the most significant variations between girdled trees and non-girdled trees with fold changes of up to 13.62. These results contribute to understanding the biological mechanism of litchi floral induction and the metabolic changes after stem girdling.

Highlights

Litchi (Litchi chinensis Sonn.) of the Sapindaceae family is a subtropical evergreen fruit tree
In this research, potted litchi trees with terminal flushed at the light green stage or mature stage were applied to evaluate the effect of stem girdling on flowering
The above results suggested that pre-treatment of stem girdling before low temperature could improve the flowering of litchi, even though the terminal flush was at a light green stage

Summary

Introduction

Litchi (Litchi chinensis Sonn.) of the Sapindaceae family is a subtropical evergreen fruit tree. Poor or unreliable flowering can cause fluctuation in litchi production. A mature and terminal flush is substantial for litchi flowering [8]. A terminal flush at the stage of turning green is a vegetative organ that would compete with reproductive organs, resulting in poor flowering and alternate bearing [9]. Drought can enhance litchi flowering at low temperatures as well [14,15]. When the cold front arrives before floral induction, the terminal shoots may be at different stages in the litchi trees, resulting in the deviation of flowering performance. Litchi growers tend to apply excessive plant growth regulators such as paclobutrazol to maintain the terminal flushes at a mature stage, which will possibly cause phytotoxicity and environmental pollution

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