Uptake, translocation and biotransformation of selenium nanoparticles in rice seedlings (Oryza sativa L.)

Abstract

Background: Selenium (Se) in soil mainly consists of selenite, selenate, and elemental Se. However, little is known about the mechanism involved in the uptake and biotransformation of elemental Se by plants.

Results: In this study, the uptake, translocation, subcellular distribution and biotransformation of selenium nanoparticles (SeNPs) in rice (Oryza sativa L.), and a comparison with selenite and selenate, were investigated through hydroponic experiments. The study revealed that SeNPs could be absorbed by rice plants; and aquaporin inhibitor was responsible for a 60.4% inhibition of SeNP influx, while metabolic inhibitor was ineffective. However, the SeNPs uptake rate of rice roots was approximately 1.7 times slower than that of selenite or selenate. Under the SeNPs or selenite treatment, Se was primarily accumulated in roots rather than in shoots, whereas an opposite trend was observed with selenate treatment. Additionally, most of the absorbed Se was distributed in cell wall of the SeNPs or selenite treated-rice plants, while its proportion was the highest in soluble cytosol of the selenate treated-rice plants. The absorbed SeNPs or selenite was rapidly assimilated to organic forms, with SeMet being the most predominant species in both shoots and roots of the rice plants. However, following selenate treatment, Se(VI) remained as the most predominant species, and only a small amount of it was converted to organic forms.

Conclusion: Therefore, this study provides a deeper understanding of the mechanisms associated SeNPs uptake and biotransformation within plants.

Keywords: Assimilation; Inorganic Se; Plants; Se nanoparticles; Subcellular distribution; Uptake.

Fig. 1

a TEM images, b hydrodynamic diameter, c zeta potential, and d EDX spectra of SeNPs

Fig. 2

Content of Se in (a) shoots and (b) roots of rice seedlings under the different SeNPs exposure time period. Data presented as mean ± SE (n = 3). Different letters indicate significant differences between the treatments at p < 0.05 according to the Duncan’s test

Fig. 3

Effect of (a) the aquaporin inhibitor AgNO₃, and (b) the metabolic inhibitor carbonyl cyanide 3-chlorophenylhydrazone (CCCP) on SeNPs influx into rice roots. Data presented as mean ± SE (n = 3). Different letters indicate significant differences between the treatments at p < 0.05 according to the Duncan’s test

Fig. 4

Content of Se in (a) shoots and (b) roots of rice seedlings under the different Se treatments. Data presented as mean ± SE (n = 3). Different letters indicate significant differences between the treatments at p < 0.05 according to the Duncan’s test

Fig. 5

Subcellular distribution of Se in (a)–(c) shoots and (d)–(f) roots of rice seedlings under the different Se treatments. F1, F2, and F3 represent cell wall, organelle, and soluble cytosol, respectively. Data presented as mean ± SE (n = 3). Different letters indicate significant differences between the treatments at p < 0.05 according to the Duncan’s test

Fig. 6

Distribution of Se in different subcellular fractions of (a) shoots and (b) roots under the different Se treatments. F1, F2, and F3 represent cell wall, organelle, and soluble cytosol, respectively

Fig. 7

Examples of the chromatograms of Se species in rice tissues extracted with protease XIV, as determined using anion exchange HPLC–UV-HG-AFS. Se species in rice tissues under (a) 10 μM SeNPs, (b) 30 μM SeNPs, (c) 10 μM selenite, and (d) 10 μM selenate treatment. 1 (unknown Se species 1); 2 (SeCys₂, selenocystine); 3 (MeSeCys, Se-methyl-selenocysteine); 4 [Se(IV), selenite]; 5 (SeMet, selenomethionine); 6 (unknown Se species 2); 7 (unknown Se species 3); 8 [Se(VI), selenate]