Copper (Cu) locally contaminates soils and might negatively affect growth and yield of crops. A better understanding
of plant copper tolerance and accumulation is needed in order to breed more Cu-tolerant or Cu-efficient
crops. Cu tolerance was evaluated in different varieties of seven species (Brassica carinata, B. juncea, B. napus,
Cynara cardunculus, Helianthus annuus, Nicotiana tabacum and Raphanus sativus) exposed to a series of CuSO4
concentrations (0.1–8 μM CuSO4) in the nutrient solution. Plants were further exposed to 0.1 μM CuSO4 and to
their variety-specific concentrations that reduced root growth to 50% of the maximum rate (EC50). Among all the
varieties of all the species the EC50 varied from 0.7 up to 3.1 μM Cu. B. carinata was significantly more Cusensitive
than the other species, which were not significantly different among each other, and B. carinata and
H. annuus accommodated significant intra-specific, inter-varietal variation. There were significant differences
between species in Cu uptake efficiency and nutrient status. When under EC50 exposure, all the Brassicaceae,
except B. carinata, maintained low Cu concentrations in shoots, whereas the other species and B. carinata
exhibited significantly increased shoot Cu concentrations, compared to the control. There was no apparent
relationship between Cu tolerance and Cu accumulation in roots and shoots, suggesting that the observed
variation in tolerance, both between and within species, is not explained by differential exclusion capacity.
Discriminant analysis and treatment comparisons suggest possible contribution of lignin, saturated fatty acids,
manganese (Mn) and zinc (Zn) in tolerance to high Cu concentrations in shoot.
