Exogenous Histidine and Glutamine Limit Cu Uptake by Vetch Plants

The interaction of low-molecular-weight chelators, including amino acids, with heavy metal cations affects their uptake and translocation in plants. However, little is known about the changes in metal-binding capacity of the cell walls (CWs) in the presence of such chelators. The aim of the present study was to clarify the effects of exogenous histidine (His) and glutamine (Gln) on Cu uptake by intact vetch (Vicia sativa L.) plants and CWs isolated from their roots and shoots. During short-term treatment exogenous His and Gln significantly reduced Cu uptake in plants, with both chelators decreasing Cu content in roots and shoots compared to Cu-only treatments. At 10 µM Cu, metal binding in the root CWs slightly increased in the presence of Gln, whereas His reduced the ability of shoot CWs to bind Cu compared to the CWs incubated in 10 µM Cu solution without chelators. However, at high Cu concentration (100 µM), both chelators lowered root CW Cu-binding capacity by 17.5–25%, while having no significant effect on shoot CWs. These findings suggest that chelation of Cu2+ ions by His and Gln can limit their interaction with CW polymers, which probably contributes to the mitigating effect of these amino acids on plant Cu uptake.