Melatonin Alleviates Drought Stress by a Non-Enzymatic and Enzymatic Antioxidative System in Kiwifruit Seedlings

Hui Xia,Mingan Liao,Huanxiu Li,Zhiyou Ni,Guochao Sun,Yi Tang,Honghong Deng,Rongping Hu,Xiulan Lv,Jin Wang,Lijin Lin,Dong Liang,Xun Wang

doi:10.3390/ijms21030852

Abstract

Although melatonin was affirmed to alleviate drought stress in various plant species, the mechanism in kiwifruit remains to be elucidated. In this study, the transcriptomes of kiwifruit leaves under control (CK), DR (drought stress), and MTDR (drought plus melatonin) treatments were evaluated. After comparisons of the gene expression between DR and MTDR, the differentially expressed genes (DEGs) were screened. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated three significant pathways, which were mainly involved in the glutathione metabolism, ascorbate and aldarate metabolism, and carotenoid metabolism. Therefore, the content and metabolic gene expression level of ascorbic acid (AsA), glutathione, and carotenoid were higher in the MTDR treatment than that in others. Furthermore, the activity and mRNA expression level of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were also promoted in the MTDR group. Combined with these results of important secondary metabolites and protective enzymes measured in the seedlings in different treatments, it could be concluded that exogenous melatonin induced the ascorbic acid-glutathione (AsA-GSH) cycle, carotenoid biosynthesis, and protective enzyme system to improve seedling growth. Our results contribute to the development of a practical method for kiwifruit against drought stress.

Highlights

Drought is becoming a fateful environmental challenge and occurs in many regions every year in the world [1,2]
With irrigation continually withheld for 9 days, the leaves of kiwifruit seedlings (DR) were gradually dehydrated and wilting (Figure 1A), and the relative water content in leaves decreased from 80.23% on 0d to 56.40% after 9 days (Figure 1B)
The results showed a starkly different gene expression pattern compared to CK with DR, while melatonin plus drought (MTDR) presented a similar expression pattern with CK, indicating that the application of melatonin before a water deficit had a significant influence on the global gene expression profile of kiwifruit leaves under drought stress

Summary

Introduction

Drought is becoming a fateful environmental challenge and occurs in many regions every year in the world [1,2]. Drought stress causes a reduction in the hydration of the membranes and proteins, leading to the damage of these components and accompanied by the excessive accumulation of reactive oxygen species (ROS), such as O2−, H2O2, 1O2, HO2−, OH·, ROOH, and ROO [3]. These ROS cause damage to chloroplast and mitochondria and degenerate the cellular structure due to their high reactivity and toxicity [4,5]. Water deficits in the growing season can negatively affect the growth and productivity of kiwifruit, which becomes a key bottleneck in the development of the kiwifruit industry in the world [9]

Methods

Results

Conclusion