Abstract
Selenium (Se) has been becoming an emerging pollutant causing severe phytotoxicity, which the biochemical mechanism is rarely known. Although hydrogen sulfide (H2S) has been suggested as an important exogenous regulator modulating plant physiological adaptions in response to heavy metal stress, whether and how the endogenous H2S regulates Se-induce phytotoxicity remains unclear. In this work, a self-developed specific fluorescent probe (WSP-1) was applied to track endogenous H2S in situ in the roots of Brassica rapa under Se(IV) stress. Se(IV)-induced root growth stunt was closely correlated with the inhibition of endogenous H2S generation in root tips. Se(IV) stress dampened the expression of most LCD and DCD homologues in the roots of B. rapa. By using various specific fluorescent probes for bio-imaging root tips in situ, we found that the increase in endogenous H2S by the application of H2S donor NaHS could significantly alleviate Se(IV)-induced reactive oxygen species (ROS) over-accumulation, oxidative impairment, and cell death in root tips, which further resulted in the recovery of root growth under Se(IV) stress. However, dampening the endogenous H2S could block the alleviated effect of NaHS on Se(IV)-induced phytotoxicity. Finally, the increase in endogenous H2S resulted in the enhancement of glutathione (GSH) in Se(IV)-treated roots, which may share the similar molecular mechanism for the dominant role of H2S in removing ROS by activating GSH biosynthesis in mammals. Altogether, these data provide the first direct evidences confirming the pivotal role of endogenous H2S in modulating Se(IV)-induced phytotoxicity in roots.
Highlights
Selenium (Se) contamination is a global environmental safety issue because Se is becoming an emerging health hazards due to the dramatic increase in Se concentration in the environment [1,2]
By using in situ fluorescent tracking of endogenous H2S, we found that the inhibition of endogenous H2S generation underlay Se(IV)-induced inhibition of root elongation in B. rapa, which could be supported by four lines of evidence
Se(IV)-induced inhibition of root elongation was closely correlated with the decrease in endogenous H2S in root tips
Summary
Selenium (Se) contamination is a global environmental safety issue because Se is becoming an emerging health hazards due to the dramatic increase in Se concentration in the environment [1,2]. The importance of Se for both human and plants has driven the long-term application of Se fertilizers in farm work, which is another important factor contributing to the increasing anthropogenic release of Se into the agricultural environment [9,10]. Se at the concentration of 4–6 ppm show remarkable inhibitory effect on the growth of both shoot and root in bean seedlings [13]. The mechanism of Seinduced phytotoxicity is rarely reported because of the limited studies about the adverse effects of Se on plants. Several studies suggest that excessive Se can trigger oxidative stress in plants by inducing the production of reactive oxygen species (ROS) and the subsequent lipid peroxidation, which may contribute to Seinduced phytotoxicity [12,13,15]. A recent study indicated that Se-induced growth stunt of root was closely associated with the disturbance of plant hormones and endogenous nitric oxide (NO)
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