Salicylic Acid Alleviates Aluminum Toxicity in Soybean Roots through Modulation of Reactive Oxygen Species Metabolism.

Ning Liu,Fengbin Song,Xiangnan Li,Zhenming Yang,Xiancan Zhu,Jiangfeng You

doi:10.3389/fchem.2017.00096

Abstract

As an important signal molecule, salicylic acid (SA) improves plant tolerance to aluminum (Al) stress. The objective of this study was to investigate the effects of exogenous SA application on the dynamics of endogenous SA and reactive oxygen species in soybean (Glycine max L.) exposed to Al stress. The roots of soybean seedlings were exposed to a combination of AlCl3 (30 μM) and SA (10 μM)/PAC (100 μM, paclobutrazol, SA biosynthesis inhibitor) for 3, 6, 9, and 12 h. Al stress induced an increase in endogenous SA concentration in a time-dependent manner, also verified by the up-regulated expression of GmNPR1, an SA-responsive gene. Al stress increased the activities of phenylalanine ammonia-lyase (PAL) and benzoic acid 2-hydroxylase (BA2H), and the contents of SA, and malondialdehyde (MDA) in the root apex. The application of exogenous SA increased PAL and BA2H, and reduced and MDA contents in soybean roots under Al stress. PAC inhibited the SA induced increase in BA2H activity. In addition, the SA application resulted in a rapid increase in hydrogen peroxide (H2O2) concentration under Al stress, followed by a sharp decrease. Compared with the plants exposed to Al alone, Al+SA plants possessed higher activities of superoxide dismutase, peroxidase, and ascorbate peroxidase, and lower catalase activity, indicating that SA alleviated Al-induced oxidative damage. These results suggested that PAL and BA2H were involved in Al-induced SA production and showed that SA alleviated the adverse effects of Al toxicity by modulating the cellular H2O2 level and the antioxidant enzyme activities in the soybean root apex.

Highlights

Aluminum (Al) is the most abundant metal and the third most abundant element in the earth’s crust after oxygen and silicon
The alleviating effect of salicylic acid (SA) on Al-induced inhibition of root elongation suggested that the inhibition of root elongation by Al may be caused by the reductions in endogenous SA concentration in soybean roots
To confirm whether Al-induced inhibition of root elongation was related to endogenous SA concentration, the concentrations of total SA were investigated at 3-h intervals over a period of 12 h (Figure 2A)

Summary

Introduction

Aluminum (Al) is the most abundant metal and the third most abundant element in the earth’s crust after oxygen and silicon. Soil acidification leads to Al solution, which is continuing, at some locations all over the world (Guo et al, 2010). The most distinct symptom of Al toxicity is inhibition of root elongation, which involves cell wall structure, plasma membrane stability, inhibition of enzyme activity, and reactive oxygen species (ROS) homeostasis in roots (Barcelo and Poschenrieder, 2002). The Al-resistance mechanisms to deal with Al toxicity include Al exclusion and internal Al tolerance (Kochian et al, 2005). Al-exclusion mechanisms rely on the Al-activated secretion of organic compounds, such as, organic acid and phenolics, from the root apex (Kochian et al, 2005). Al-tolerance mechanisms involve detoxification of Al related to modification of the root cell wall structure and Al translocation from roots to shoots (Kochian et al, 2015)

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