Surface coating-modulated toxic responses to silver nanoparticles in Wolffia globosa

Area of Science:

• Environmental Science
• Plant Biology
• Nanotechnology

Background:

• Silver nanoparticles (AgNPs) are increasingly prevalent in consumer products, raising concerns about their environmental release and impact on ecosystems.
• The biochemical mechanisms by which plants mitigate nanoparticle toxicity are not well understood, necessitating research into plant-nanoparticle interactions.
• Aquatic plants, like Wolffia globosa, are crucial in freshwater ecosystems and can be directly exposed to nanoparticles and dissolved silver ions.

Purpose of the Study:

• To investigate the differential physiological and biochemical responses of Wolffia globosa exposed to silver ions (Ag+) and AgNPs coated with either adenosine triphosphate (ATP-nAg) or citrate (cit-nAg).
• To elucidate how surface coating on AgNPs influences their toxicity and the plant's defense mechanisms.
• To understand the role of specific metabolic pathways and nutrient uptake in plant adaptation to silver stress.

Main Methods:

• Exposure of Wolffia globosa to varying concentrations of Ag+, ATP-nAg, and cit-nAg.
• Assessment of Hill reaction activity, chlorophyll and soluble protein content, sugar accumulation, and antioxidant enzyme activities (superoxide dismutase, peroxidase).
• Measurement of nutrient uptake (P, K, Fe, Cu) and silver accumulation within the plant tissues.

Main Results:

• Cit-nAg exhibited significantly lower toxicity compared to ATP-nAg and Ag+, preserving Hill reaction activity.
• ATP-nAg and Ag+ treatments led to reduced chlorophyll and protein, increased antioxidant activity, and sugar depletion, while cit-nAg caused sugar accumulation.
• Surface coating influenced nutrient uptake, with cit-nAg primarily affecting copper uptake, whereas Ag+ and ATP-nAg impacted phosphorus, potassium, iron, and copper uptake.

Conclusions:

• The surface coating of AgNPs critically determines their phytotoxicity and the plant's biochemical response mechanisms.
• Citrate coating may facilitate metabolic pathways like the tricarboxylic acid cycle and pentose phosphate pathway, mitigating toxicity.
• ATP coating might provide an exogenous energy source, influencing plant metabolism differently compared to citrate or free silver ions.