Lead (Pb) is among the most toxic heavy metals in biological systems and causes toxicity from seed germination to yield formation. High Pb concentrations lead to oxidative damage and impair water relation and nutrition uptake in plants. Rye (Secale cereale L.) is an abiotic stress-tolerant crop, distributed in Eastern and Central Europe. Pb concentration in soils higher than 30 mg kg-1 is commonly toxic to plants. This study investigated the effects of different Pb concentrations [0, 100, 200 and 400 mu M of Pb(NO3)2] on mineral element concentrations (B, Ca, Cu, Fe, K, Mg, Mn, Na and Zn) in rye plants. After 15 days of Pb stress, the levels of mineral elements (B, Ca, Cu, Fe, K, Mg, Zn, Mn and Na), and Pb accumulation were detected using by ICP-OES (Inductively coupled plasma-optical emission spectrometry) in leaves and roots. Under 0, 100, 200 and 400 mu M Pb application, the Pb accumulation varied between 0.005-2.94 and 5.63-13.63 mg kg-1 in leaves, and 0.03-69.34-168.11-329.74 mg kg-1 in roots, respectively. Roots accumulated higher levels of Pb than the leaves. The amounts of Na, Fe and B concentrations reduced, whereas the contents of Ca, K, Mn, Cu, and Zn increased in both leaves and roots in a concentration-dependent manner. The maximum rate of increase or decrease in elemental contents was recorded for 400 mu M Pb-exposed plants. In addition, Mg content increased in leaves, but decreased in roots. Overall, our findings suggest that Pb-exposure causes alterations in mineral element concentrations in a concentration-dependent manner, which could be useful to make risk assessments for Pb pollution in agricultural lands.

Woody plants have received considerable attention for the phytoremediation of heavy metal-contaminated soil. This study aimed to investigate the changes in antioxidant enzyme activity, macroelement uptake and microstructure of the woody plant Robinia pseudoacacia (black locust) for the phytoremediation of cadmium (Cd) and lead (Pb) co-contaminated soil based on dynamic sampling. The results show that black locust demonstrates strong tolerance in Cd and Pb co-contaminated soil. After 30-120 days of cultivation, the activities of superoxide dismutase, peroxidase and the macroelement (potassium [K] and calcium [Ca]) content in plant leaves significantly declined in response to Cd and Pb. However, after 160 d of cultivation, the antioxidant enzyme activities, chlorophyll, sulfhydryl and soluble protein contents, as well as Ca and magnesium content in plant leaves were returned to normal levels under the 40 mg kg(-1) Cd and 1000 mg kg(-1) Pb contaminated soil (CdPb3). Meanwhile, K content in plant leaves under the CdPb3 treatment was significantly (P < 0.05) increased by 68.9% compared with the control. Cadmium and Pb were primarily accumulated in black locust roots. Scanning electron microscope analysis indicated that the sieve tubes in the roots and stems of plant might block the transport of Cd and Pb. Transmission electron microscope analysis indicated that the number and volume of osmiophilic particles in plant leaves were increased and the cell walls were thickened in response to Cd and Pb stress. Path analysis further indicated that the growth of plant was related to macroelements uptake and physiological change (photosynthesis, antioxidant enzyme activity and chelation). Thus, black locust could effectively regulate the antioxidant defense system, macroelement absorption and microstructure to enhance plant tolerance to Cd and Pb stress. Moreover, black locust could maintain the normal urease, acid phosphatase and sucrase activities in the Cd and Pb co-contaminated soil. These findings suggest that black locust could be considered as a useful woody plant for the phytostabilization in Cd- and Pb-contaminated soil.

Background and aimsCadmium (Cd) contamination poses a potential threat to plant growth and human health. In this study, we aimed to determine the effect of selenium nanoparticles (SeNPs) on Cd and selenium (Se) uptake and accumulation in bok choy, and investigate the detoxification mechanism of SeNPs on bok choy under Cd stress.MethodsA pot culture was performed in Cd-contaminated soil with soil applied and foliar-sprayed SeNPs, including SLow, SHigh, FLow, FHigh, and corresponding control treatment. The soil available Cd content, Cd and Se fractions in soil, elements accumulation, subcellular Cd/Se distribution, MDA content, SOD activity, and Fourier transformed infrared spectroscopy (FTIR) were evaluated.ResultsSoil applied SeNPs significantly reduced Cd concentration by 25.9-42.4%, and Cd uptake rate by 33.4-37.8%. Further, soil applied SeNPs had no significant effect on available Cd but did affect Se fractions in soil. Additionally, soil applied SeNPs increased Se concentration by 3.1 - 6.3 times in bok choy and caused a higher Se concentration in root than in shoot, with the residual and organic matter-bound Se mainly affecting Se accumulation in shoot. However, foliar-sprayed SeNPs had no significant effect on Cd uptake but increased Se accumulation by 2.4 - 33.0 times in bok choy. Soil applied and foliar-sprayed SeNPs prompted the distribution of Cd in cell wall and in soluble component in shoot, respectively, which reduced the damage of Cd on organelle.ConclusionSoil applied SeNPs was an effective method for reducing Cd accumulation and improving Se biofortification and mineral elements accumulation in bok choy.