Abstract
The contamination of soils with cadmium (Cd) has become a serious environmental issue that needs to be addressed. Elucidating the mechanisms underlying Cd accumulation may facilitate the development of plants that accumulate both high and low amounts of Cd. In this study, a combination of phenotypic, physiological, and comparative transcriptomic analyses was performed to investigate the effects of different Cd concentrations (0, 5, 10, 30, 50 mg/kg) on Brassica juncea L. Our results suggest that B. juncea L. seedlings had a degree of tolerance to the 5 mg/kg Cd treatment, whereas higher Cd stress (10–50 mg/kg) could suppress the growth of B. juncea L. seedlings. The contents of soluble protein, as well as MDA (malondialdehyde), were increased, but the activities of CAT (catalase) enzymes and the contents of soluble sugar and chlorophyll were decreased, when B. juncea L. was under 30 and 50 mg/kg Cd treatment. Comparative transcriptomic analysis indicated that XTH18 (xyloglucan endotransglucosylase/hydrolase enzymes), XTH22, and XTH23 were down-regulated, but PME17 (pectin methylesterases) and PME14 were up-regulated, which might contribute to cell wall integrity maintenance. Moreover, the down-regulation of HMA3 (heavy metal ATPase 3) and up-regulation of Nramp3 (natural resistance associated macrophage proteins 3), HMA2 (heavy metal ATPase 2), and Nramp1 (natural resistance associated macrophage proteins 1) might also play roles in reducing Cd toxicity in roots. Taken together, the results of our study may help to elucidate the mechanisms underlying the response of B. juncea L. to various concentrations of Cd.
Highlights
Cadmium (Cd) has long been recognized as a serious environmental problem due to the expansion of industrialization and urbanization (Li et al, 2014; Zhao et al, 2015)
Pearson correlation analysis demonstrated that the Cd concentration in the soils exhibited a significant negative correlation with plant height, fresh weight, and total leaf area (r > 0.9, P < 0.05; Figures 1B–D and Supplementary Table 3), suggesting that Cd treatment suppressed the growth of B. juncea L. seedlings in a dose-effect pattern
We found that most of xyloglucan endotransglucosylase/hydrolase enzymes (XTHs) (12/14), including all the copies of three XTH18, XTH22, and XTH23 were down-regulated in B. juncea L. roots under Cd treatment (Figure 6)
Summary
Cadmium (Cd) has long been recognized as a serious environmental problem due to the expansion of industrialization and urbanization (Li et al, 2014; Zhao et al, 2015). Several strategies have been established to prevent the negative effects of Cd, such as immobilization, soil washing, and phytoremediation using plants (Wuana and Okieimen, 2011; Li et al, 2014). Among these strategies, plant breeding or engineering could represent an efficient approach to either increase the Cd concentration in nonedible plant organs for phytoremediation or reduce that in edible plant organs (Grant et al, 2008; Mahar et al, 2016; Tang et al, 2017). Improving understanding of the Cd uptake, transport, and accumulation mechanisms could be very helpful in developing both high and low Cd accumulation plants
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