|Ebbs, Stephen - SO ILLINOIS U-CARBONDALE|
|Lau, Ingar - CORNELL UNIVERSITY|
|Ahner, Beth - CORNELL UNIVERSITY|
Submitted to: Plant Physiology
Publication Type: Abstract Only
Publication Acceptance Date: June 18, 2000
Publication Date: N/A
Technical Abstract: Phytochelatins (PCs) are non-protein metal binding peptides that are enzymatically synthesized in response to heavy metal stress in plants. The key enzyme phytochelatin synthase is activated primarily by cadmium (Cd), although other metals may stimulate PC production. Phytochelatins are believed to have a role in Cd tolerance, forming a Cd-PC complex that is sequestered in cell vacuoles. Thlaspi caerulescens is a heavy metal hyperaccumulator that accumulates metals such as Zn and Cd to high concentrations (40,000 and 4,000 ppm, respectively) without exhibiting phytotoxicity. The mechanism of metal tolerance has not been characterized but also reportedly involves metal sequestration in cell vacuoles. This study was conducted to ascertain the role of PCs in metal tolerance in Thlaspi caerulescens and the related non-accumulator Thlaspi arvense. Plants of each species were exposed to a range of Cd concentrations (0-50 uM) and then metal and PC levels were quantified in root and shoot tissue. Although PCs were produced by both species in response to Cd exposure, these peptides do not appear to be involved in metal tolerance in the hyperaccumulator. Shoot and root PC levels for both species showed a similar positive correlation with tissue Cd, but total PC levels in shoots of the hyperaccumulator were generally lower, despite the correspondingly higher tissue metal concentrations were. The lack of a role for PCs in the hyperaccumulator's response to metal stress suggests that another ligand might be involved in Cd tolerance. The lower level of shoot PCs in T. caerulescens, despite higher tissue Cd levels, also implies that Cd complexed in the root is transported to the shoot and sequestered in a compartment or form that does not elicit a PC response.