Influence of Root-Applied Glutathione on Nickel Uptake and Distribution in Brassica Roots

Abstract

Glutathione (GSH) is a biologically active tripeptide composed of glutamate, cysteine, and glycine. To elucidate early plant responses to nickel (Ni), an essential but potentially toxic micronutrient, we investigated how locally applied GSH to the roots influences Ni movement in hydroponically grown Brassica napus plants. Although plants require trace amounts of Ni, a slight increase in soil Ni can induce toxicity and impair plant growth. Therefore, understanding the molecular mechanisms underlying Ni tolerance in plants is crucial for improving crop productivity. Plants were exposed to treatments for 2 days to capture early responses. Exogenous GSH application to the roots suppressed Ni uptake and shoot translocation. Micro-PIXE analysis was used to visualize the Ni distribution within the roots and showed distinct radial transport patterns between the root tips and upper regions. GSH treatment reduced Ni accumulation near the stele, suggesting that GSH inhibited the radial transport of Ni toward the central vascular tissues. Transcriptome analysis showed that genes associated with lignin biosynthesis were upregulated by Ni treatment alone, whereas some of these genes were downregulated by Ni + GSH treatment. Plants may modulate the root cell wall structure to regulate Ni mobility, and GSH influences this process at the molecular level. Elucidating the GSH-dependent mechanisms controlling Ni transport can contribute to developing cultivation strategies to enhance plant Ni tolerance.