Physiological Mechanism of Enhancing Salt Stress Tolerance of Perennial Ryegrass by 24-Epibrassinolide.

Wenli Wu,Erik H Ervin,Xunzhong Zhang,Qiang Zhang,Zhiping Yang

doi:10.3389/fpls.2017.01017

Wenli Wu, Erik H Ervin + Show 3 more

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https://doi.org/10.3389/fpls.2017.01017

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Abstract

Brassinosteroids (BR) regulate plant tolerance to salt stress but the mechanisms underlying are not fully understood. This study was to investigate physiological mechanisms of 24-epibrassinolide (EBR)'s impact on salt stress tolerance in perennial ryegrass (Lolium perenne L.) The grass seedlings were treated with EBR at 0, 10, and 100 nM, and subjected to salt stress (250 mM NaCl). The grass irrigated with regular water without EBR served as the control. Salt stress increased leaf electrolyte leakage (EL), malondialdehyde (MDA), and reduced photosynthetic rate (Pn). Exogenous EBR reduced EL and MDA, increased Pn, chlorophyll content, and stomatal conductance (gs). The EBR applications also alleviated decline of superoxide dismutase (SOD) and catalase (CAT) and ascorbate peroxidase (APX) activity when compared to salt treatment alone. Salt stress increased leaf abscisic acid (ABA) and gibberellin A4 (GA4) content but reduced indole-3-acetic acid (IAA), zeatin riboside (ZR), isopentenyl adenosine (iPA), and salicylic acid (SA). Exogenous EBR at 10 nm and 100 nM increased ABA, and iPA content under salt stress. The EBR treatment at 100 nM also increased leaf IAA, ZR, JA, and SA. In addition, EBR treatments increased leaf proline and ions (K+, Mg2+, and Ca2+) content, and reduced Na+/K+ in leaf tissues. The results of this study suggest that EBR treatment may improve salt stress tolerance by increasing the level of selected hormones and antioxidant enzyme (SOD and CAT) activity, promoting accumulation of proline and ions (K+, Ca2+, and Mg2+) in perennial ryegrass.

Highlights

Salinity is a major abiotic stress limiting growth and development of plants in many areas of the world due to increasing use of low quality of water for irrigation and soil salinization, and more than 20% of cultivated land worldwide (∼45 hectares) is affected by salt stress and the amount is increasing (Gupta and Huang, 2014)
The results of this study showed that salt stress at 250 mM NaCl caused significant damage to perennial ryegrass
Our results showed that EBR treatments increased gs and Photosynthetic Rate (Pn), suggesting that EBR may improve gas exchange and cell membrane integrity

Summary

Introduction

Salinity is a major abiotic stress limiting growth and development of plants in many areas of the world due to increasing use of low quality of water for irrigation and soil salinization, and more than 20% of cultivated land worldwide (∼45 hectares) is affected by salt stress and the amount is increasing (Gupta and Huang, 2014). Salinity stress may cause damage to plant physiological processes by over accumulation of reactive oxygen species (ROS), ion toxicity, impairment of antioxidant defense systems, photosynthetic function, and imbalance of hormones (Hu et al, 2012, 2015; Kim et al, 2016). Plants have developed antioxidant defense mechanisms to eliminate ROS and prevent oxidative damage. Antioxidant enzymes, such as superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), and ascorbate peroxidase (APX, EC 1.11.1.11), protect plants against oxidative stress (Huang et al, 2014; Zhang et al, 2015). SOD constitutes the first line of defense against ROS by dismutating the superoxide anion to H2O2, which is finely regulated by CAT, POD, and APX (Gupta and Huang, 2014). Various antioxidant metabolites and enzymes may work coordinately in suppressing ROS toxicity under stressful environments

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