Melatonin Enhances Cold Tolerance by Regulating Energy and Proline Metabolism in Litchi Fruit.

Gangshuai Liu,Meijiao Hu,Zhengke Zhang,Jialiang Liu,Yueming Jiang,Ze Yun,Yuxin Zhang

doi:10.3390/foods9040454

Abstract

Melatonin (MLT) is a vital signaling molecule that regulates multiple physiological processes in higher plants. In the current study, the role of MLT in regulating chilling tolerance and its possible mechanisms in litchi fruit during storage at ambient temperatures after its removal from refrigeration was investigated. The results show that the application of MLT (400 μM, dipping for 20 min) to ‘Baitangying’ litchi fruit effectively delayed the development of chilling injury (CI) while inhibiting pericarp discoloration, as indicated by higher chromacity values (L*, a*, b*) and anthocyanin levels. MLT treatment suppressed the enhancements of the relative electrical conductivity (REC) and malondialdehyde (MDA) content, which might contribute to the maintenance of membrane integrity in litchi fruit. MLT treatment slowed the decline in cellular energy level, as evidenced by higher adenosine triphosphate (ATP) content and a higher energy charge (EC), which might be ascribed to the increased activities of enzymes associated with energy metabolism including H+-ATPase, Ca2+-ATPase, succinate dehydrogenase (SDH), and cytochrome C oxidase (CCO). In addition, MLT treatment resulted in enhanced proline accumulation, which was likely a consequence of the increased activities of ornithine-δ-aminotransferase (OAT) and Δ1-pyrroline-5-carboxylate synthase (P5CS) and the suppressed activity of proline dehydrogenase (PDH). These results suggest that the enhanced chilling tolerance of litchi fruit after MLT treatment might involve the regulation of energy and proline metabolism.

Highlights

The fruit of litchi (Litchi chinensis Sonn.) plants are important tropical and subtropical crops with high commercial value due to their intriguing red pericarp, delicious taste, and abundant nutritional content [1]
An extremely significant (p < 0.01) lower chilling injury (CI) index was detected in the MLT-treated fruit throughout the 20 h of storage at 25 ◦ C
The results showed that 400 μM MLT treatment markedly retarded the development of CI and prevented pericarp discoloration, as shown by the higher chromacity L*, a*, b* values and anthocyanin content in the MLT-treated fruit

Summary

Introduction

The fruit of litchi (Litchi chinensis Sonn.) plants are important tropical and subtropical crops with high commercial value due to their intriguing red pericarp, delicious taste, and abundant nutritional content [1]. Some difficulties exist concerning the refrigeration of litchi because fruit quality can be subjected to gradual reduction during cold storage and undergo severe deterioration within hours once the chilled fruit are. Some safe strategies (such as chitosan-coating [6], modified atmosphere packing [7,8], combined applications of organic acid dipping and foil wrapping [9], L-cysteine application [10], kojic acid treatment [11], and methionine solution immersion [12]) have been demonstrated to ameliorate the chilling stress-induced browning of litchi fruit, there is still an imperative requirement to explore more methods that can reliably enhance the cold tolerance of litchi fruit

Methods

Results

Discussion

Conclusion