Aluminum toxicity is discussed, including general effects (symptoms and physiological effects), differential aluminum tolerance in plants, beneficial effects of aluminum, and the genetic control of aluminum tolerance. Manganese and iron toxicity are discussed in the same framework. The toxicity of other metals (Zn, Cu, Ni, Cd, and Pb) is also discussed, though not as extensively as aluminum, manganese, and iron. 476 references.

The Physiology of Metal Toxicity in Plants

Heavy metal pollution is one of the most troublesome environmental problems faced by mankind nowadays. Copper, in particular, poses serious problems due to its widespread industrial and agricultural use. Unlike other heavy metals, such as cadmium, lead, and mercury, copper is not readily bioaccumulated and thus its toxicity to man and other mammals is relatively low. On the contrary, plants in general are very sensitive to Cu toxicity, displaying metabolic disturbances and growth inhibition at Cu contents in the tissues only slightly higher than the normal levels. The reduced mobility of Cu in soil and sediments, due to its strong binding to organic and inorganic colloids, constitutes, in a way, a barrier to Cu toxicity in land plants. In aqueous media, however, plants are directly exposed to the harmful effects of Cu and, thus, algae and some species of aquatic higher plants are more easily subjected to Cu toxicity. Excess Cu inhibits a large number of enzymes and interferes with several aspects of plant biochemistry, including photosynthesis, pigment synthesis, and membrane integrity. Perhaps its most important effect is associated with the blocking of photosynthetic electron transport, leading to the production of radicals which start peroxidative chain reactions involving membrane lipids. Copper effects on plant physiology are wide ranging, including interference with fatty acid and protein metabolism and inhibition of respiration and nitrogen fixation processes. At the whole plant level Cu is an effective inhibitor of vegetative growth and induces general symptoms of senescence. The high toxicity of Cu to plants has led to the evolution of several strategies of defense. Among the most important ones is the production of Cu-complexing compounds. Although the nature, structure, and function of these compounds is still controversial, they can be divided into two main groups: metallothionein-like compounds and phytochelatins. The latter appears to constitute the most widespread response of plants to stresses provoked by metals, including Cu.

Biochemical, physiological, and structural effects of excess copper in plants

Toxicity and Tolerance in the Responses of Plants to Metals

Chromium and nickel

SUMMARY
The order of toxicity of different metals affecting root growth of seedlings of rye grass (Lolium perenne S24) was: copper > nickel > manganese > lead > cadmium > zinc > aluminium > mercury > chromium > iron. With the sole exception of manganese, these results confirm those of other studies and the order follows that of the stability of the metallic-organic complexes. The results are of value in predicting the toxicity of heavy metals in plant growth on contaminated soils.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1982.tb03310.x

A comparison of the toxicity of heavy metals, using root elongation of rye grass, lolium perenne

SUMMARY Three clones of Agrostis gigantea were evaluated for their tolerance to cobalt, copper, nickel and zinc. Of the clones originating from a mine waste site in Sudbury, Ontario, one showed tolerance to copper, cobalt, and nickel, the other only to nickel. Neither of these clones showed tolerance to zinc. A clone from a seed supply house lacked tolerance to any of the metals tested. Copper was most toxic to A. gigantea, followed by nickel, cobalt and zinc.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1979.tb02298.x

Tolerance and toxicity of cobalt, copper, nickel and zinc in clones of agrostis gigantea

Role of Copper Binding, Absorption, and Translocation in Copper Tolerance of Agrostis gigantea Roth

A mine waste site from Sudbury, Ontario, contaminated with heavy metals is described. The dominant vegetative cover was formed by two grasses: Agrostis gigantea Roth, and Agrostis scabra Willd. Testing of 10 clones of A. gigantea from the roast bed and an adjoining area for copper tolerance showed that two clones collected from the roast bed were tolerant to increased copper levels. Copper tolerance was found in clones growing on soils with high copper contents and low pHs. The combination of high copper content and low pH brought about a high level of extractable copper within the soil. Soils with equally high copper levels but higher pHs and therefore low extractable-copper levels did not support copper-tolerant clones.

Copper tolerance in clones of Agrostis gigantea from a mine waste site

A number of soils were examined from areas of a mine waste contaminated with heavy metals. Soils from areas vegetated with Agrostis gigantea Roth, which did not possess copper tolerance were compared with adjacent barren areas. Soils from sites which supported non-tolerant grasses had higher pHs and were lower in water-extractable metals than soils from non-vegetated areas. The soils did not differ with respect to any other factor examined. The non-vegetated soils were shown to be more toxic to the growth of Avena sativa than vegetated soils. The establishment and survival of grasses not having the selective advantage of copper tolerance were found to be restricted to the less toxic regions of the study site.

Gary D. Hogan

Papers

Tolerance and toxicity of cobalt, copper, nickel and zinc in clones of agrostis gigantea

Role of Copper Binding, Absorption, and Translocation in Copper Tolerance of Agrostis gigantea Roth

Copper tolerance in clones of Agrostis gigantea from a mine waste site

The effects of soil factors on the distribution of Agrostis gigantea on a mine waste site

The effects of soil factors on the distribution of Agrostis gigantea on a mine waste site [feed grasses].