Exogenous melatonin improves salt tolerance in tomato by regulating photosynthetic electron flux and the ascorbate–glutathione cycle

Zepeng Yin,Jiazhi Lu,Sida Meng,Yiling Liu,Islam Mostafa,Mingfang Qi,Tianlai Li

doi:10.1080/17429145.2019.1645895

Zepeng Yin, Jiazhi Lu + Show 5 more

Open Access

https://doi.org/10.1080/17429145.2019.1645895

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Abstract

ABSTRACT Melatonin (MT) can protect plants against abiotic stress. In order to explore whether melatonin can improve photosynthetic function under NaCl stress, Solanum lycopersicum L. cv. Liaoyuanduoli were exposed to 150 mmol L−1 NaCl stress with or without pretreatment with 150 μmol L−1 melatonin. The results showed that NaCl stress can lead to reduced chlorophyll content, lower photosynthetic function, increased reaction oxygen species (ROS) levels, and decreased PSII activity. These changes were mainly due to the reduction in oxygen-evolving complex (OEC) activity on the donor side of PSII and the blockage of electron transfer from QA to QB on receptor side of PSII. The donor side of PSII was more sensitive to NaCl stress relative to the receptor side of PSII. Interestingly, application of MT enhanced tomato NaCl tolerance. MT reduced the production of ROS by balancing the distribution of photosynthetic electron flux, facilitated the repair of PSII by maintaining the abundance of Psb O and D1, and promoting the ability of the donor and acceptor sides of PSII to deliver electrons. MT also enhanced the scavenging ability of ROS by stimulating the activity of enzymes involved in the AsA-GSH cycle.

Highlights

Soil salinity is a common abiotic stress that limits agricultural yield and productivity worldwide (Munns and Tester 2008)
Effects of MT on chlorophyll content and carbon assimilation under NaCl stress To test whether MT treatment reduced the effects of NaCl stress in tomato plants, chlorophyll content of the leaves was measured by evaluating changes in leaf color (Figure 1)
Seedlings that were treated with NaCl for seven days showed significant 40.65% reduction in net photosynthetic rate (Pn) compared to untreated plants, while photosynthetic rates (Pn) decreased by 20.33% in seedlings that were exposed to MT and NaCl compared to the untreated control

Summary

Introduction

Soil salinity is a common abiotic stress that limits agricultural yield and productivity worldwide (Munns and Tester 2008). Superfluous electrons induced by reduced OEC activity either on the donor or the receptor sides of PSII can be transferred either to oxygen in PSI or generate reactive oxygen species (ROS) through a Mehler reaction (Foyer and Noctor 2009). These excessive electrons can leak and attack free oxygen molecules. Salt stress generates reactive oxygen species (ROS) and damages PSII reaction centers, further leading to the peroxidation and dissociation of the thylakoid membranes (Zhang et al 2012). Melatonin (MT) is an effective exogenous substance that is widely used to ameliorate the effects of stress on crops (Galano et al 2011; Zhang et al 2015b)

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