Quantitative Relationship between Cadmium Uptake and the Kinetics of Phytochelatin Induction by Cadmium in a Marine Diatom.

Yun Wu,Xinlei Ge,Li Zhang,Qiaoguo Tan,Wei Zhang,Mindong Chen,Zhiqiang Guo

doi:10.1038/srep35935

Abstract

Heavy metals activate the synthesis of phytochelatins (PCs), while the induced PCs might affect metal uptake via chelating intracellular free metals. However, the relationship of PCs to metal uptake is poorly understood. In this study, we examined the kinetics of cadmium (Cd) accumulation and the synthesis of PCs in a marine diatom, Thalassiosira weissflogii, under different irradiance levels. Irradiance alone could not change the concentrations of PCs in the Cd-free treatments, while higher irradiance accelerated the induction of intracellular PCs at the same [Cd2+] level. PC-SH (2 × PC2 + 3 × PC3 + 4 × PC4) was bound with Cd at a stoichiometric ratio of 2 to 49 in our short-term uptake experiments, indicating that PC induction is sufficient to serve as the first line of defense against Cd stress. A positive linear correlation between the induction rate of PCs and the Cd uptake rate was observed, while the ratio of the PC content to intracellular Cd varied greatly when the irradiance was increased several fold. Because metal uptake has been successfully used in predicting acute metal toxicity, our findings are helpful for understanding the role of PCs in metal detoxification and developing PCs as biomarkers for metal sensitivity.

Highlights

Metal contamination in aquatic ecosystems is a global environmental problem
Changes in the PC induction rate and metal uptake rate were investigated with a regression analysis to determine whether there was any correlation between Cd uptake and the kinetics of PC induction by Cd
A linear relationship between the intracellular Cd concentration and the exposure time was observed for all irradiance and [Cd2+] treatments (Fig. 1), and the slope of the linear regression was calculated to obtain the Cd uptake rate, which was plotted as a function of dissolved [Cd2+] (Fig. 2)

Summary

Introduction

Metal contamination in aquatic ecosystems is a global environmental problem. Phytoplankton, which has a considerable biomass, is the entry point for metals into the aquatic food web and is important from the perspective of ecotoxicology and human health. To deal with the stress due to elevated environmental Cd, phytoplankton may have evolved both extracellular and intracellular strategies to alleviate metal toxicity. PCs are known as specific intracellular chelators in phytoplankton and respond rapidly to metal exposure[8,9,10]. PCs sequester metals by chelating metal with the sulfhydryl groups in the PC cysteines. Since their identification thirty years ago, considerable efforts have been made to explore the possibility of using PCs as biomarkers of metal stress[11,12]. The corresponding synthesis of PCs during a 4-h exposure period was quantified to investigate how irradiance influences PC induction.

Methods

Results

Conclusion