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  Section: Plant Nutrition » Other Beneficial Elements » Cobalt
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Cobalt Tolerance by Plants

  Microorganisms and Lower Plants
    - Algae
    - Fungi
    - Moss
  Higher Plants
Uptake and Transport
  Absorption as Related to Properties of Plants
  Absorption as Related to Properties of Soil
  Accumulation as Related to the Rhizosphere
Cobalt Metabolism in Plants
Effect of Cobalt in Plants on Animals
Interaction of Cobalt with Metals and Other Chemicals in Mineral Metabolism
  Interaction of Cobalt with Iron
  Interaction of Cobalt with Zinc
  Interaction of Cobalt with Cadmium
  Interaction of Cobalt with Copper
  Interaction of Cobalt with Manganese
  Interaction of Cobalt with Chromium and Tin
  Interaction of Cobalt with Magnesium
  Interaction of Cobalt with Sulfur
  Interaction of Cobalt with Nickel
  Interaction of Cobalt with Cyanide
Beneficial Effects of Cobalt on Plants
  Drought Resistance
  Alkaloid Accumulation
  Vase Life
  Biocidal and Antifungal Activity
  Ethylene Biosynthesis
  Nitrogen Fixation
Cobalt Tolerance by Plants
  Higher Plants

Stonewort (Chara vulgaris L.) resistant to metal pollution, when cultivated in a natural medium containing CoCl2 showed high level of cobalt in dry matter as insoluble compounds (120). On the other hand, a copper-tolerant population of a marine brown alga (Ectocarpus siliculosus Lyng.) had an increased tolerance to cobalt. The copper-tolerance mechanism of other physiological processes may be the basis of this cotolerance (121).

A genetically stable cobalt-resistant strain, CoR, of Neurospora crassa Shear & Dodge, exhibited an approximately ten-fold higher resistance to CO2+ than the parent strain. The CO2+ toxicity was reversed by Mg2+, but not by Fe3+, indicating that the CO2+did not affect iron metabolism. Alternatively, the mechanism of resistance probably involves an alteration in the pattern of iron metabolism so that the toxic concentration of cobalt could not affect the process (122). Magnesium (Mg2+) may reverse the toxicity of CO2+, either by increasing the tolerance to high intracellular concentration of heavy metal ions or by controlling the process of uptake and accumulation of ions (123). In several mutants of Aspergillus niger growing in toxic concentrations of Zn2+, CO2+, Ba2+, Ni 2+, Fe3+, Sn2+, and Mn2+, the resistance is due to an intracellular detoxification rather than defective transport. Each mutation was due to a single gene located in its corresponding linkage group.

Toxicity of metals is reversed in the wild-type strain by definite amounts of K+, NH4+, Mg2+, and Ca2+. These competitions between pairs of cations indicate a general system responsible for the transport of cations (124). In Aspergillus fumigatus, cobalt increased thermophily at 45°C and fungal tolerance at 55°C (125).

Higher Plants
In higher plants, cobalt tolerance has been mainly reported in members of ‘advanced’ families such as the Labiatae and Scrophulariaceae growing in the copper-field belt of Shaba (Zaire) (126). Among these plants, Haumaniastrum robertii, a copper-tolerant species, is also a cobalt-accumulating plant. The plant contains abnormally high cobalt (about 4304 µg g-1 dry weight), far exceeding the concentration of copper. This species has the highest cobalt content of any phanerogam (127). Haumaniastrum katangense and H. robertii grow on substrates containing 0 to 10,000 µg Co g-1. Although they can accumulate high concentrations of cobalt, an exclusion mechanism operates in these species at lower concentrations of the element in the soil. Uptake of cobalt was not linked to a physiological requirement of the element. The plant–soil relationship for Co was significantly high enough for these species to be useful in the biogeochemical prospecting for cobalt (128). Tolerance and accumulation of copper and cobalt were investigated in three members of phylogenetic series of taxa within the genus Silene (Caryophyllaceae) from Zaire, which were regarded as representing a progression of increasing adaptation to metalliferous soils. Effects of both metals (singly and in combination) on seed germination, seedling and plant performances, yield, and metal uptake from soil culture confirmed the ecotypic status of S. burchelli, which is a more tolerant variant of the nontolerant S. burchelli var. angustifolia. But both the ecotype and metallophyte variants of S. cobalticola are relatively more tolerant to copper than to cobalt.

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