Interaction of Cobalt with Metals and Other Chemicals in Mineral Metabolism
The interaction of cobalt with other metals depends to a major extent on the concentration of the metals
used. The cytotoxic and phytotoxic responses of a single metal or combinations are considered in
terms of common periodic relations and physicochemical properties, including electronic structure,
ion parameters (charge-size relations), and coordination. But, the relationships among toxicity, positions,
and properties of these elements are very specific and complex
(65). The mineral elements in
plants as ions or as constituents or organic molecules are of importance in plant metabolism. Iron,
copper, and zinc are prosthetic groups in certain plant enzymes. Magnesium, manganese, and cobalt
may act as inhibitors or as activators. Cobalt may compete with ions in the biochemical reactions of
several plants
(66,67).
Iron
Many trace elements in high doses induce iron deficiency in plants
(68). Combinations of increased
cobalt and zinc in bush beans have led to iron deficiency
(69). Excess metals accumulated in shoots,
and especially in roots, reduce ion absorption and distribution in these organs, followed by the
induction of chlorosis, decrease in catalase activity, and increase in nonreducing sugar concentration
in barley
(70,71). Supplying chelated iron ethylenediamine di(o-hydroxyphenyl) acetic acid
[Fe-(EDDHA),] could not overcome these toxic effects in Phaseolus spp. L.
(72). Simultaneous
addition of cobalt and zinc to iron-stressed sugar beet (Beta vulgaris L.) resulted in preferential
transport of cobalt into leaves followed by ready transport of both metals into the leaf symplasts
within 48 h
(73). A binuclear binding site for iron, zinc, and cobalt has been observed
(74).
Zinc
Competitive absorption and mutual activation between zinc and cobalt during transport of one or
the other element toward the part above the ground were recorded in pea (Pisum sativum L.) and
wheat seedlings
(75). Enrichment of fodder beet (Beta vulgaris L.) seeds before sowing with one
of these cations lowers the content of the other in certain organs and tissues. It is apparently not the
result of a simple antagonism of the given cations in the process of redistribution in certain organs
and tissue, but is explained by a similar effect of cobalt and zinc as seen when the aldolase and carbonic
anhydrase activities and intensity of the assimilators’ transport are determined
(76).
Cobalt tends to interact with zinc, especially in high doses, to affect nutrient accumulation
(77). The
antagonism is sometimes related to induced nutrient deficiency
(69). In bush beans, however, cobalt
suppressed to some extent the ability of high concentration of zinc to depress accumulation of potassium,
calcium, and magnesium. The protective effect was stated to be the result of zinc depressing the
leaf concentration of cobalt rather than the other nutrients
(69). Substitution of Zn
2+ by CO
2+ reduces
specificity of Zn
2+ metalloenzyme acylamino-acid-amido hydrolase in Aspergillus oryzae Cohn
(78).
Cadmium
Combinations of elements may be toxic in plants when the individual ones are not
(72). Trace elements
usually give protective effects at low concentrations because some trace elements antagonize the
uptake of others at relatively low levels. For example, trace elements in various combinations
(Cu–Ni–Zn, Ni–Co–Zn–Cd, Cu–Ni–Co–Cd, Cu–Co–Zn–Cd, Cu–Ni–Zn–Cd, and Cu–Ni–Co–Zn–Cd)
on growth of bush beans protected against the toxicity of cadmium. It was suggested that part of the
protection could be due to cobalt suppressing the uptake of cadmium by roots. Other trace elements in
turn suppressed the uptake of cobalt by roots
(69). These five trace elements illustrated differential partitioning
between roots and shoots
(40). The binding of toxic concentration of cobalt in the cell wall of
the filamentous fungus (Cunninghamella blackesleeana Lender) was totally inhibited and suppressed
by trace elements
(79).
Copper
The biphasic mechanism involved in the uptake of copper by barley roots after 2 h was increased
with 16 µM CO
2+, but after 24 h, a monophasic pattern developed with lower values of copper
absorption, indicating an influence of CO
2+ on the uptake site
(80).
Manganese
Cobalt and zinc increased the accumulation of manganese in the shoots of bush beans grown for
3 weeks in a stimulated calcareous soil containing Yolo loam and 2% CaCO
3 (40).
Chromium and Tin
The inhibitory effects of chromium and tin on growth, uptake of NO
3- and NH
4+, nitrate reductase,
and glutamine synthetase activity of the cyanobacterium (Anabaena doliolum Bharadwaja) was
enhanced when nickel, cobalt, and zinc were used in combination with test metals in the growth
medium in the following degree: Ni>Co>Zn
(81).
Magnesium
The activating effect of cobalt on Mg
2+-dependent activity of glutamine synthetase by the
blue–green alga Spirulina platensis Geitler may be considered as an important effect. Its effect in
maintaining the activity of the enzyme in vivo is independent of ATP
(82).
Sulfur (Sulphur)
The mold Cunninghamella blackesleeana Lendner, grown in the presence of toxic concentration of
cobalt, showed elevated content of sulfur in the mycelia. Its cell wall contained higher concentrations
of phosphate and chitosan, citrulline, and cystothionine as the main cell wall proteins
(79).
Nickel
In moss (Timmiella anomala Limpricht), nickel overcomes the inhibitory effect of cobalt on protonemal
growth whereas cobalt reduces the same effect of nickel on bud number
(83).
Cyanide
Cyanide in soil was toxic to bush beans and also resulted in the increased uptake of the toxic elements
such as copper, cobalt, nickel, aluminum, titanium, and, to a slight extent, iron. The phytotoxicity
from cyanide or the metals led to increased transfer of sodium to the leaves and roots
(40).