Zinc exposure has differential effects on uptake and metabolism of sulfur and nitrogen in Chinese cabbage

Abstract

Zinc (Zn) is a plant nutrient; however, at elevated levels it rapidly becomes phytotoxic. In order to obtain insight into the physiological background of its toxicity, the impact of elevated Zn2+ concentrations (1 to 10 μM) in the root environment on physiological functioning of Chinese cabbage was studied. Exposure of Chinese cabbage (Brassica pekinensis) to elevated Zn2+ concentrations (≥ 5 μM) in the root environment resulted in leaf chlorosis and decreased biomass production. The Zn concentrations of the root and shoot increased with the Zn2+ concentration up to 68‐fold and 14‐fold, respectively, at 10 μM compared to the control. The concentrations of the other mineral nutrients of the shoot were hardly affected by elevated Zn2+ exposure, although in the root both the Cu and Fe concentrations were increased at ≥ 5 µM, whereas the Mn concentration was decreased and the Ca concentration strongly decreased at 10 µM Zn2+. The uptake and metabolism of sulfur and nitrogen were differentially affected at ≥ 5 µM Zn2+. Zn2+ exposure resulted in an increase of sulfate uptake and the activity of the sulfate transporters in the root, and in enhanced total sulfur concentration of the shoot, which could be ascribed partially to an accumulation of sulfate. Moreover, Zn2+ exposure resulted in an up to 6.5‐fold increase in water‐soluble non‐protein thiol (and cysteine) concentration of the root. However, nitrate uptake by the root and the nitrate and total nitrogen concentrations of the shoot were decreased upon Zn2+ exposure, demonstrating the absence of a mutual regulation of the uptake and metabolism of sulfur and nitrogen at toxic Zn levels. Evidently, elevated Zn2+ concentrations in the root environment did not only disturb the uptake, distribution and assimilation of sulfate, it also affected the uptake and metabolism of nitrate in Chinese cabbage.

Molecular speciation and tissue compartmentation of zinc in durum wheat grains with contrasting nutritional status

“…However, the resulting increase in grain S concentration in both the HN–MZn and the HN–HZn was substantially higher than what could be deduced from differences in S‐treatments, which underlines the synergism between Zn, N and S enrichment. Increases in sulfate uptake by increasing Zn applications or increasing tissue Zn concentrations have been shown previously, supporting the findings in the present study (Coolong & Randle, ; Stuiver et al ., ).…”

Physiological and Growth Responses in the (Schizolobium amazonicum Huber ex Ducke) Seedlings Subjected to Cadmium Doses

“…Cadmium effects on photosynthesis lie on blocking energy dissipation in the form of heat (ATP), which prevents energy from being absorbed in the reaction centers of photosystem II. According to Parmar et al (2014), it happens due to thylakoid destructuring, which reduces the photochemical efficiency of these photosynthetically active membranes. Another probable explanation for this result lies on the direct inhibition of chlorophyll synthesis or on restrictions in Mg absorption and translocation, since the magnesium found in chloroplasts works as protector by inhibiting the action of cadmium and preventing the transport of electrons (Benavides et al, 2005;Martins et al, 2013, Zhang et al, 2014.…”

Synergy between cadmium and zinc in bean plants cultivated in multi contaminated soils

“…Although Zn is considered an essential element, exposure at high concentrations causes damage to photosystem II by interacting with the thiol group of their proteins. Moreover, excess Zn can inhibit Mg absorption, reducing the photosynthetic capacity (Parmar, Freek, & Shahbaz, 2014).…”