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Copper [Cu, 29]
plant roots is present in both metallic and organic complexes. It is relatively slightly
mobile, and thus its concentrations are higher in roots than in shoots. Its concentration increases with plant growth. Contents of Cu in various plants from unpolluted
regions of different countries range from X to XO mg/kg. However, under both natural and human-induced conditions, several species of plants can accumulate much
more Cu, especially in roots and storage tissues.
Copper is an essential metal in plants and plays a significant role in various physiological processes, such as respiration, photosynthesis, water permeability, protein metabolism, and functions of various enzymes, involved mainly in the oxidation– reduction
reactions. In several enzymes (e.g., plastocyanin and phenoloxydase), Cu is linked by
the metal-S-cluster. It is involved in the synthesis of DNA and RNA, and in mechanisms of disease resistance (mainly to fungal diseases) of plants (Marschner 2005).
Copper deficiency affects physiological processes, and therefore the plant production. Cu deficiency in crops is widespread, especially in Europe. Common crop
plants that are highly sensitive to the Cu deficiency are wheat, oats, sunflower, alfalfa,
carrot, lettuce, spinach, onion, and citrus trees. Cu-deficiency level in plants show
genetic differences; however, in most cases, the Cu levels about 2 mg/kg are likely to
be inadequate for most plants. Despite the general Cu tolerance of most plant species
and genotypes, its excess is highly toxic. Copper toxicity to plants may occur when
its contents in soils range between 25 and 40 mg/kg, and soil pH is below 5.5. The
most common symptoms of its toxicity are (1) Cu-induced chlorosis, resulted in the
low photosynthesis efficiency; (2) damage to DNA; (3) damage to membrane permeability; (4) disturbed protein complexes; and (5) root malformation.
Several plants and bacteria are resistance to excess Cu, mainly due to its binding
by small proteins (Puig et al. 2007). Cu-tolerant plants and Cu hyperaccumulators
have been broadly used in geochemical prospecting for Cu-ore deposits (KabataPendias and Pendias 1999). Among various native plants grown in the polluted area
of the Northern Europe (Kola Peninsula), crowberry (Empetrum nigrum) has the
highest capacity to accumulate Cu, at the pollution-background ratio of 33 (Reimann
et al. 2001).
Plants growing in Cu-polluted sites may accumulate elevated amounts of this
metal. Especially, plants from the Cu-smelter regions and from the plantations using
Cu fungicides may contain its extremely high levels, over 1000 mg/kg. This is of a
real problem, especially in old plantations of citrus, coffee, cacao, tea, olives, and
vineyards, where Cu fungicides have been applied for a long time.
There are several interactions between Cu and both major and trace elements in
soils. The most serious interactions are as follows:
r Cu absorption is reduced at high P levels
r Cu deficiency in plants with high levels of N
r Cu low availability to plants at high levels of CuCO 3 or other Cu compounds
r Cu–Zn, competitive inhibition of root absorption
r Cu–Fe, increased levels of both metals decreases their absorption
r Cu–Mn, interactions are related to N metabolism
r Cu–Mn, interactions are both synergistic and antagonistic in the uptake
processes under variable conditions