Abstract
Selenium (Se) is suggested as an emerging pollutant in agricultural environment because of the increasing anthropogenic release of Se, which in turn results in phytotoxicity. The most common consequence of Se-induced toxicity in plants is oxidative injury, but how Se induces reactive oxygen species (ROS) burst remains unclear. In this work, histofluorescent staining was applied to monitor the dynamics of ROS and nitric oxide (NO) in the root of Brassica rapa under Se(IV) stress. Se(IV)-induced faster accumulation of NO than ROS. Both NO and ROS accumulation were positively correlated with Se(IV)-induced inhibition of root growth. The NO accumulation was nitrate reductase (NR)- and nitric oxide synthase (NOS)-dependent while ROS accumulation was NADPH oxidase-dependent. The removal of NO by NR inhibitor, NOS inhibitor, and NO scavenger could alleviate Se(IV)-induced expression of Br_Rbohs coding for NADPH oxidase and the following ROS accumulation in roots, which further resulted in the amelioration of Se(IV)-induced oxidative injury and growth inhibition. Thus, we proposed that the endogenous NO played a toxic role in B. rapa under Se(IV) stress by triggering ROS burst. Such findings can be used to evaluate the toxic effects of Se contamination on crop plants.
Highlights
Selenium (Se) is an essential and beneficial micronutrient for plants [1]
Blocking NADPH oxidase activity alleviated Se-induced membrane lipids oxidation (Figure 3D), the loss of membrane integrity (Figure 3E), and growth inhibition (Figure 3F). These results suggested that Se(IV)-induced oxidative injury and growth inhibition resulted from NADPH oxidasemediated over-generation of reactive oxygen species (ROS)
The enzymatic assay indicated that treatment with Se(IV) induced the increases in nitrate reductase (NR) and nitric oxide synthase (NOS) activity as compared to their control groups, respectively (Figure 6C, D). These results suggested that Se(IV) exposure could induce the rapid accumulation of endogenous nitric oxide (NO) through both NOS- and NR-dependent pathway
Summary
Selenium (Se) is an essential and beneficial micronutrient for plants [1]. The important roles of Se in intrinsic physiological process has been confirmed by the identification of Se-containing proteins in plant cells [2,3]. The excessive Se in agricultural environment poses potential threat to the growth of crop plants by causing phytotoxicity [12,13,14]. The lack of knowledge on the mechanism of Se-induced phytotoxicity limits the evaluation of the toxic effect of Se on crop plants. Several recent studies have suggested that the excessive Se could induce oxidative stress in plants by triggering the production of reactive oxygen species (ROS) [15,16,17]. How Se induces ROS generation and the subsequent oxidative injury in plants remains unclear. NADPH oxidase coding by Rbohs (respiratory burst oxidative homologues) has been suggested as a major source for ROS generation in plants under both biotic and abiotic stresses [18]. The stimulated NADPH oxidase activity in plants has been associated with heavy metal stress [20,21,22], but the comprehensive regulation of different Rboh members by heavy metals (including Se) is hardly known
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