Methyl Jasmonate Regulates Antioxidant Defense and Suppresses Arsenic Uptake in Brassica napus L.

Muhammad A Farooq,Weijun Zhou,Basharat Ali,Rafaqat A Gill,Shuiping He,Hongbo Liu,Jianxiang Xu,Faisal Islam

doi:10.3389/fpls.2016.00468

Abstract

Methyl jasmonate (MJ) is an important plant growth regulator, involved in plant defense against abiotic stresses, however, its possible function in response to metal stress is poorly understood. In the present study, the effect of MJ on physiological and biochemical changes of the plants exposed to arsenic (As) stress were investigated in two Brassica napus L. cultivars (ZS 758 – a black seed type, and Zheda 622 – a yellow seed type). The As treatment at 200 μM was more phytotoxic, however, its combined application with MJ resulted in significant increase in leaf chlorophyll fluorescence, biomass production and reduced malondialdehyde content compared with As stressed plants. The application of MJ minimized the oxidative stress, as revealed via a lower level of reactive oxygen species (ROS) synthesis (H2O2 and OH-) in leaves and the maintenance of high redox states of glutathione and ascorbate. Enhanced enzymatic activities and gene expression of important antioxidants (SOD, APX, CAT, POD), secondary metabolites (PAL, PPO, CAD) and induction of lypoxygenase gene suggest that MJ plays an effective role in the regulation of multiple transcriptional pathways which were involved in oxidative stress responses. The content of As was higher in yellow seeded plants (cv. Zheda 622) as compared to black seeded plants (ZS 758). The application of MJ significantly reduced the As content in leaves and roots of both cultivars. Findings of the present study reveal that MJ improves ROS scavenging through enhanced antioxidant defense system, secondary metabolite and reduced As contents in both the cultivars.

Highlights

Arsenic (As) pollution is an important environmental issue due to its toxicity and accumulation in irrigated areas where it causes serious threats to sustainable agriculture production (Heikens, 2006)
Application of Methyl jasmonate (MJ) to As stressed (MJ 1 + 200 μM) plants improved the dry weight of cultivars ZS 758 and Zheda 622 by 31 and 27% respectively, in shoot and 18 and 23%, respectively, in root when compared with As stressed plants (Table 1)
Exogenous application of MJ significantly reduced the As concentration in the leaves and roots of both B. napus cultivars under As stress and better effect was observed at 1 μM MJ (Table 1)

Summary

Introduction

Arsenic (As) pollution is an important environmental issue due to its toxicity and accumulation in irrigated areas where it causes serious threats to sustainable agriculture production (Heikens, 2006). Arsenic contamination in soil from both anthropogenic and natural resources is an increasing concern, especially in Asian countries like India and Bangladesh (Zhao et al, 2010a,b) and its consumption in the food chain poses serious threats to human health. This contaminant (As) exists in different chemical forms in which As(III) is considered more phytotoxic due to its interference with the sulfhydryl groups of enzymes and proteins. ROS and subsequent oxidative stress may be the common mechanism of phytotoxicity and cause of damage to important organic constituent of plant cells (Petrov et al, 2015). The use of exogenous plant growth regulators to enhance the plant tolerance against metal stress condition has been given much attention (Bartwal et al, 2013; Li et al, 2014; Ali et al, 2015)

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Discussion

Conclusion