Assessing the relative contributions of phytochelatins and the cell wall to cadmium resistance in white lupin

Abstract

In response to Cd stress, higher plants utilise a number of defence systems, such as retention in cell walls, binding by organic molecules in the cytosol and sequestration in the vacuole. White lupin is a Cd-resistant legume that is of interest for phytoremediation of acidified and Cd-contaminated soils. The aim of this research was to evaluate the contributions of various mechanisms of Cd detoxification used by this species, focusing on cell-wall retention and binding by thiol-rich compounds. Retention of Cd by the cell wall of white lupin was well described by a Langmuir isotherm model. The percentage of total Cd adsorbed by the cell wall ranged from 29 to 47% in leaves, from 38 to 51% in stems and from 26 to 42% in roots depending on the Cd supply. Cadmium induced the synthesis of high levels of phytochelatins (PCs) in lupin plants, mainly in roots, with PC 3 being the major PC. The amount of Cd complexed by thiols accounted for approximately 20% of the total Cd in leaves, 40% in stems and 20% in roots. Therefore, cell-wall retention could account for more than twice the amount of Cd complexed by PCs in leaves and roots. In stems, both mechanisms contributed equally to Cd detoxification. These studies indicate that white lupin plants use cell-wall binding and, secondarily, the production of PCs, as effective mechanisms of Cd detoxification.

Contributions of apoplasmic cadmium accumulation, antioxidative enzymes and induction of phytochelatins in cadmium tolerance of the cadmium-accumulating cultivar of black oat (Avena strigosa Schreb.)

“…5a, b). In white lupin, a greater than 6 M Cd treatment disabled binding of a large part of Cd to cell walls and increased Cd inXux and caused toxicity (Vázquez et al 2006). These observations suggest that not only the Cd accumulation in cell walls, but also antioxidative abilities and vacuolar compartmentation are all important for resistance to Cd toxicity.…”

“…The Cd distribution in cell walls of T. caerulescens is indicated as one major mechanism in Cd detoxiWcation as well as vacuolar compartmentation (Cosio et al 2004(Cosio et al , 2005. The capacity of root cell walls in binding Cd 2+ is indicated as an important factor determining the Cd inXux into cells (Nishizono et al 1989;Lozano-Rodriguez et al 1997;Vázquez et al 2006). In this study, we evaluated Cd distribution to cell walls in black oat cultivars diVering in Cd sensitivity (Fig.…”

“…In contrast to PCs, involvement of Cd accumulation in the cell wall fraction in Cd tolerance has attracted less attention in spite of its importance for metal tolerance. In roots, the capacity of binding Cd 2+ to cell walls is suggested as a principal factor limiting the Cd inXux into cells (Nishizono et al 1989;Lozano-Rodriguez et al 1997;Vázquez et al 2006). In Cd/Zn hyperaccumulator T. caerulescens, Cd accumulation in cell walls has been suggested as one of the major factors in Cd detoxiWcation in addition to Cd compartmentation in vacuoles (Cosio et al 2004(Cosio et al , 2005.…”

Exogenous nitric oxide enhances cadmium tolerance of rice by increasing pectin and hemicellulose contents in root cell wall

“…However, other mechanisms that contribute to NO-induced increase of Cd tolerance remains unclear. The production of phytochelatins (PCs) is the secondarily eVective mechanism of Cd detoxiWcation in white lupin (Vázquez et al 2006), and the functions of PCs in Cd tolerance have been widely proved (cobbett 2000). It has been shown that Cd accumulation is accompanied by a rapid induction of PCs biosynthesis and that the content of PCs is theoretically suYcient to chelate all Cd taken up; this protects photosynthesis but does not prevent a decline in the transpiration rate (Haag-Kerwer et al 1999).…”

“…Since previous evidence supports that NO aVects cellulose content in tomato roots cell walls in a dose-dependent manner (Correa-Aragunde et al 2008) and plant cell wall plays a key role in reducing Cd accumulation in the protoplast (Vázquez et al 2006), it was hypothesized that NO could be involved in the regulation of root cell wall composition in alleviating heavy Cd toxicity to plants. This study provides the Wrst evidence indicating that exogenous NO alleviates Cd toxicity to rice by increasing pectin and hemicellulose contents in root cell wall, increasing Cd accumulation in root cell wall and decreasing Cd accumulation in soluble fraction of leaves.…”