Enhancement of cadmium accumulation in sweet sorghum as affected by nitrate

Abstract

• The Cadmium (Cd)-polluted soils are is an increasing concern worldwide. Phytoextraction of Cd pollutants by high biomass plants, such as sweet sorghum, is considered an environmentally-friendly, cost-effective and sustainable strategy for remediating this problem. Nitrogen (N) is a macronutrient essential for plant growth, development and stress resistance. Nevertheless, how nitrate, as an important form of N, affects Cd uptake, translocation and accumulation in sweet sorghum is still unclear. • In the present study, a series of nitrate levels (N1, 0.5 mM; N2, 2 mM; N3, 4 mM; N4, 8 mM and N5, 16 mM) with or without added 5 μM CdCl 2 treatment in sweet sorghum was investigated hydroponically. • The results indicate that Cd accumulation in the aboveground parts of sweet sorghum was enhanced by optimum nitrate supply, resulting from both increased dry weight and Cd concentration. Although root-to-shoot Cd translocation was not enhanced by increased nitrate, some Cd was transferred from cell walls to vacuoles in leaves. Intriguingly, expression levels of Cd uptake and transport genes, SbNramp1, SbNram-p5 and SbHMA3, were not closely related to increased Cd as affected by nitrate supply. The expression of SbNRT1.1B in relation to nitrate transport showed an inverted 'U' shape with increasing nitrate levels under Cd stress, which was in agreement with trends in Cd concentration changes in aboveground tissues. • Based on the aforementioned results, nitrate might regulate Cd uptake and accumulation through expression of SbNRT1.1B rather than SbNramp1, SbNramp5 or SbHMA3, the well-documented genes related to Cd uptake and transport in sweet sorghum.

Nitrate Increases Cadmium Accumulation in Sweet Sorghum for Improving Phytoextraction Efficiency Rather Than Ammonium

“…Compositions of full-strength nutrient solution were macro-nutrient including K 2 SO 4 , 1.0 mM; KH 2 PO 4 , 0.2 mM; MgSO 4 , 0.5 mM and micro-nutrient including Fe-EDTA, 200 μM; H 3 BO 3 , 5 μM; MnSO 4 , 2 μM; ZnSO 4 , 0.5 μM; CuSO 4 , 0.3 μM; (NH 4 ) 2 Mo 7 O 24 , 0.01 μM. Nitrogen source was supplied as 4 mM NO 3 – (N) in the form of Ca(NO 3 ) 2 or 4 mM NH 4 + (A) in the form of NH 4 Cl, and nitrogen concentration was selected according to our previous study in sweet sorghum ( Bai et al, 2021 ). To compensate the extra Ca 2+ introduced by Ca(NO 3 ) 2 , CaCl 2 was added in the treatments without NO 3 – addition.…”

“…Compositions of full-strength nutrient solution were macro-nutrient including K 2 SO 4 , 1.0 mM; KH 2 PO 4 , 0. (A) in the form of NH 4 Cl, and nitrogen concentration was selected according to our previous study in sweet sorghum (Bai et al, 2021). To compensate the extra Ca 2+ introduced by Ca(NO 3 ) 2 , CaCl 2 was added in the treatments without NO 3 − addition.…”

Integration of transcriptome and metabolome analyses reveals sorghum roots responding to cadmium stress through regulation of the flavonoid biosynthesis pathway

“…Hyperaccumulators are plants capable of growing in soils with high levels of contamination and able to concentrate high levels of toxins in their tissues. Cd hyperaccumulators have been used worldwide tophyto-extract the metals from the contaminated soils in an eco-friendly and green approach (Guan et al, 2019;Bai et al, 2020).…”