Cadmium-induced sulfate uptake in maize roots

Area of Science:

• Plant Physiology
• Environmental Toxicology
• Molecular Biology

Background:

• Cadmium (Cd) is a toxic heavy metal that affects plant physiology.
• Phytochelatin (PC) biosynthesis is a key plant defense mechanism against heavy metals, requiring sulfur.
• Sulfate uptake is crucial for providing sulfur to plants.

Purpose of the Study:

• To investigate the effect of cadmium on high-affinity sulfate transport in maize roots.
• To understand the relationship between cadmium exposure, sulfate uptake, and phytochelatin biosynthesis.
• To elucidate the molecular mechanisms underlying cadmium-induced changes in sulfate transport.

Main Methods:

• Maize (Zea mays) were treated with 10 micromolar CdCl2 in nutrient solutions.
• Sulfate, potassium, and phosphate uptake rates were measured.
• Electrophysiological measurements (membrane potential, pH) and H(+)-ATPase activity were assessed.
• Enzyme kinetics (Km, Vmax) for sulfate transport were determined.
• Northern-blot analysis was used to examine gene expression.

Main Results:

• Cadmium exposure doubled sulfate uptake in maize roots, with no effect on potassium or phosphate uptake.
• Increased sulfate uptake was not linked to changes in proton motive force or plasma membrane H(+)-ATPase activity.
• Kinetics analysis revealed a doubling of Vmax for high-affinity sulfate transport without altering Km.
• Cadmium increased mRNA levels for a putative high-affinity sulfate transporter.
• Sulfate and glutathione levels decreased, while PCs increased significantly.

Conclusions:

• Cadmium specifically enhances high-affinity sulfate transport in maize roots.
• This enhancement is mediated by pretranslational regulation of the sulfate transporter gene.
• The increased sulfate uptake is essential for meeting the sulfur requirements of cadmium-induced phytochelatin biosynthesis.