Cadmium-stress in nodulated white lupin: strategies to avoid toxicity

White lupin plants (Lupinus albus L., cv. Multolupa) were grown hydroponically on perlite with different Cd concentrations in the nutrient solution (μM): 0, 18 and 45. Changes in growth, nodulation, nutrient concentrations, nutrient uptake and distribution, Cd bound to cell wall and some Cd stress indicators were studied in roots and shoots (leaves plus stem) of 35-d-old plants as a result of Cd uptake. A significant decrease in both root and shoot dry weight was found only when plants were grown on 45 μM Cd, whereas nodulation and total N content decreased for both Cd levels. White lupin plant retained up to 88% of total Cd in the roots, showing some capacity of Cd translocation to the upper parts, but an important fraction of Cd was bound to the cell walls. Cadmium addition reduced P, K, Fe, Mn and Zn concentrations in the shoot and Mn in the root. Despite the reduction in Mn concentration, Mn level in Cd-treated plants remained within normality, probably because white lupin is a Mn accumulator. In Cd-treated plants, the level of lipid peroxidation remained unmodified, whereas total thiols showed a pronounced increase in roots. Results obtained suggest that white lupin has developed several strategies of defence against Cd, as a high retention of Cd by cell walls and complexation by thiol groups, both contributing to diminish the level of free Cd. Moreover, the high Mn content of white lupin could contribute to the prevention of Cd damage on photosynthesis, since chlorosis was not found.