Several species from the Brassica genus are very important agricultural crops in different parts of the world and are also known to be heavy metal accumulators. There have been a large number of studies regarding the tolerance, uptake and defense mechanism in several of these species, notably Brassica juncea and B. napus, against the stress induced by heavy metals. Numerous studies have also been published about the capacity of these species to be used for phytoremediation purposes but with mixed results. This review will focus on the latest developments in the study of the uptake capacity, oxidative damage and biochemical and physiological tolerance and defense mechanisms to heavy metal toxicity on six economically important species: B. juncea, B. napus, B. oleracea, B. carinata, B. rapa and B. nigra.

In this work, the effect of excess copper (Cu) on tomato plants grown in hydroponic solutions for up to 15 days was studied. The solutions contained different Cu concentrations ranging from 0.05, 0.15, 0.20, and 0.35 mM Cu. Dry mass, root length, and foliar area decreased with time and Cu solution concentration. Copper accumulated more heavily in roots than in leaves. Mineral uptake was affected by increasing Cu concentrations in solution with calcium (Ca), iron (Fe), and zinc (Zn) contents in leaves decreasing. Except for Ca, the concentrations of these elements in the roots also decreased, which indicated that root uptake was affected and the translocation to upper plant parts was disrupted. Iron leaf deficiency was the probable cause of the observed chlorosis and decrease in chlorophyll levels. The activities of three enzymes studied in leaves (guaiacol peroxidases (GPOD), catalase (CAT), and polyphenol oxidase (PPO)) increased transiently, probably as an early response mechanism against Cu induced oxidative stress. At higher Cu concentrations, this defense mechanism broke down and the activities of the enzymes decreased accordingly.