Copper pre-exposure reduces AgNP bioavailability to wheat.

Area of Science:

• Environmental Science
• Plant Biology
• Nanotoxicology

Background:

• Heavy metals at contaminated sites can influence plant interactions with emerging contaminants like engineered silver nanoparticles (AgNPs).
• The mechanisms governing these interactions, particularly the impact of pre-existing metal stress on AgNP uptake and toxicity, are not well understood.

Purpose of the Study:

• To investigate how prior copper (Cu) exposure affects wheat (Triticum aestivum L.) seedling responses to subsequent silver nanoparticle (AgNP) exposure.
• To elucidate the underlying physiological mechanisms, including root cell death and thiol content, mediating these interactions.

Main Methods:

• Wheat seedlings were hydroponically exposed to varying concentrations of copper (Cu) for 4 days.
• Root Cu concentrations, cell death (Evans blue uptake), and total thiol content (HPLC) were measured.
• Seedlings were subsequently exposed to 10 mg L^-1 AgNPs for 8 hours, and Ag influx rates were determined.

Main Results:

• Cu exposure significantly increased root Cu concentrations, root tip cell death, and altered total thiol levels in wheat roots.
• Pre-exposure to Cu led to a 1.3-3.9 fold decrease in silver (Ag) influx rates upon subsequent AgNP exposure.
• Reduced Ag influx correlated with increased cell death and altered thiol levels in Cu-pre-exposed plants.

Conclusions:

• Plant responses to AgNPs are significantly modulated by pre-existing heavy metal contamination.
• Cell death and changes in thiol metabolism in roots play a key role in mediating the reduced AgNP uptake observed in metal-stressed plants.
• The bioavailability of AgNPs may be overestimated if the presence of other metals at contaminated sites is not considered.