Ascorbate-Mediated Modulation of Cadmium Stress Responses: Reactive Oxygen Species and Redox Status in Brassica napus.

Ha-Il Jung,Mi-Jin Chae,Bok-Rye Lee,Myung-Sook Kim,Eun-Jin Lee,Goo-Bok Jung,Tae-Gu Lee,Jinwook Lee

doi:10.3389/fpls.2020.586547

Abstract

The role of ascorbate (AsA) in antioxidant defense system-associated resistance to cadmium (Cd) in oilseed rape plants has not yet been clearly demonstrated. The present study investigated the critical role of exogenous AsA on the physiological and biochemical responses of reactive oxygen species (ROS) and antioxidant scavenging defense systems in oilseed rape (Brassica napus L. cv. Tammi) seedlings exposed to Cd. Cd (10 μM) treatment led to significant reductions in plant growth; increases in the levels of superoxide anion radical, hydrogen peroxide, and malondialdehyde; and increases in Cd uptake and accumulation by the roots and shoots in hydroponically grown 10-day-old seedlings. Moreover, it reduced AsA content and AsA redox ratios, which have been correlated with reductions in glutathione (GSH) and/or nicotinamide adenine dinucleotide phosphate (NADPH) redox status. However, exogenously applying AsA to Cd-exposed seedlings decreased Cd-induced ROS, improved antioxidant defense systems by increasing AsA, GSH, and NADPH contents, and increased Cd uptake and accumulation in both roots and shoots of the plants. These results provided evidence that the enhancement in AsA redox status can be linked to an increase in the GSH and/or NADPH redox ratios through the induction of the AsA–GSH–NADPH cycle. Thus, these results suggest that exogenous AsA application to oilseed rape seedlings under Cd stress might alleviate the overall Cd toxicity by regulating the homeostasis of the AsA–GSH–NADPH cycle, which reestablishes the steady-state cellular redox status.

Highlights

Cadmium (Cd) pollution is rapidly increasing because of global urbanization and industrialization, whereas the concomitant increase in contaminated farmland and agricultural water supplies has serious effects on the safety of agricultural production
We evaluated the effects of AsA on Cd uptake, Cd accumulation, reactive oxygen species (ROS) production, and redox homeostasis, all of which are related to Cd-induced phytotoxicity, in oilseed rape grown under Cd-contaminated conditions
In the oilseed rape seedlings treated with Cd alone, the Cd content was significantly higher in the roots than that in the shoots

Summary

Introduction

Cadmium (Cd) pollution is rapidly increasing because of global urbanization and industrialization, whereas the concomitant increase in contaminated farmland and agricultural water supplies has serious effects on the safety of agricultural production. In addition to inhibiting normal plant growth, Cd can replace the cofactors of essential metal ions in important proteins through the Fenton reaction (Peroza et al, 2009 Jung et al, 2015; Jung et al, 2016; Singh et al, 2016; Loix et al, 2017; Jung et al, 2018b) This process generates reactive oxygen species (ROS), such as the superoxide anion radical (O2·−), hydrogen peroxide (H2O2), hydroxyl radicals (OH·), and so on. Cd toxicity can be counteracted using various physiological and biochemical detoxification systems to alleviate or minimize oxidative stress caused by excessive absorption and accumulation of Cd (Kim et al, 2008; Srivastava et al, 2014; Singh et al, 2016; Jung et al, 2017, 2018b)

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