216
Trace Elements in Abiotic and Biotic Environments
there is an assumption that Mo–S amino acid complexes are involved in this process.
Also, some proteins are identified as transporters of Mo within plant cells (Fitri et al.
vide Kabata-Pendias 2011).
Molybdenum is the essential component of several enzymes, such as nitrate
reductase, xanthine dehydrogenase, sulfite oxidase, and several other enzymes. It is
also involved in enzymatic activities of DNA and RNA. The basic enzymatic role of
Mo is its functions a redox carrier, and is apparently reflected in its valence change.
Plant requirement for Mo is related to N supply; plants supplied with NH 4 –N have
less need for Mo, than those supplied with NH 3 –N. It is essential to microorganisms. Especially Rhizobium bacteria, as well as other N-fixing microorganisms have
a large requirement for Mo, which may be concentrated up to 100 mg/kg. Number
and weight of root nodules of clover significantly increase with elevated mobile Mo
species in soils.
The most important Mo function in plants is NO 3 reduction, thus its deficiency in
plants is similar to those of N deficiency. The correction of Mo deficiency may be
accomplished by Mo application in soil and foliar or seed treatments. However, the
preferable control of Mo deficiency is liming the soil to a pH around 6.5, as uncontrolled increase of Mo, especially in fodder plants, may be toxic to animals.
Several complex interactions between Mo and other elements have an impact on
both its availability and physiological function.
Mo–Cu antagonism is strongly related to N and S metabolisms, and has variable
impact on Mo uptake by plants. Soil factors that increase Mo availability usually
have inhibitory effects on the Cu uptake. Also, increased levels of SO 4
2 reduce the
Cu absorption, which may have an impact on undesirable Mo–Cu ratio in fodder
plants. There are several interactions between Mo and other elements:
r Mo–Mn antagonism is associated with soil acidity; liming of soil for the
correction of Mo deficiency may increase Mn toxicity.
r Mo–Fe interaction is relatively complex, but is associated mainly with
Fe–Mo precipitates within root tissues that may limit Mo mobility.
r Mo–V and Mo–W interactions are due to possible substitution between
these elements in several biochemical processes.
r Mo–P interaction is contradictory, as P fertilizers on Mo mobility is variable, depending on some other soil factors.
r Mo–Ca interaction is complex and highly cross-linked with the soil pH.
In general, Mo contents of plants, within the range of 0.1–0.5 mg/kg, are sufficient for their metabolism, whereas concentrations in the range of 10–50 mg/kg
are toxic to most plant species. Only some legumes and cruciferous plants require
more Mo.
Molybdenum concentrations in plants closely reflect its mobile pool in soils, as it
is readily taken up by plants, when present in soluble species. Molybdenum is always
more available from neutral and alkaline soils than from acidic ones. Some plants,
particularly legumes, may accumulate very high amounts of Mo, up to 350 mg/kg,
without toxicity symptoms.
Trace Elements in Abiotic and Biotic Environments
there is an assumption that Mo–S amino acid complexes are involved in this process.
Also, some proteins are identified as transporters of Mo within plant cells (Fitri et al.
vide Kabata-Pendias 2011).
Molybdenum is the essential component of several enzymes, such as nitrate
reductase, xanthine dehydrogenase, sulfite oxidase, and several other enzymes. It is
also involved in enzymatic activities of DNA and RNA. The basic enzymatic role of
Mo is its functions a redox carrier, and is apparently reflected in its valence change.
Plant requirement for Mo is related to N supply; plants supplied with NH 4 –N have
less need for Mo, than those supplied with NH 3 –N. It is essential to microorganisms. Especially Rhizobium bacteria, as well as other N-fixing microorganisms have
a large requirement for Mo, which may be concentrated up to 100 mg/kg. Number
and weight of root nodules of clover significantly increase with elevated mobile Mo
species in soils.
The most important Mo function in plants is NO 3 reduction, thus its deficiency in
plants is similar to those of N deficiency. The correction of Mo deficiency may be
accomplished by Mo application in soil and foliar or seed treatments. However, the
preferable control of Mo deficiency is liming the soil to a pH around 6.5, as uncontrolled increase of Mo, especially in fodder plants, may be toxic to animals.
Several complex interactions between Mo and other elements have an impact on
both its availability and physiological function.
Mo–Cu antagonism is strongly related to N and S metabolisms, and has variable
impact on Mo uptake by plants. Soil factors that increase Mo availability usually
have inhibitory effects on the Cu uptake. Also, increased levels of SO 4
2 reduce the
Cu absorption, which may have an impact on undesirable Mo–Cu ratio in fodder
plants. There are several interactions between Mo and other elements:
r Mo–Mn antagonism is associated with soil acidity; liming of soil for the
correction of Mo deficiency may increase Mn toxicity.
r Mo–Fe interaction is relatively complex, but is associated mainly with
Fe–Mo precipitates within root tissues that may limit Mo mobility.
r Mo–V and Mo–W interactions are due to possible substitution between
these elements in several biochemical processes.
r Mo–P interaction is contradictory, as P fertilizers on Mo mobility is variable, depending on some other soil factors.
r Mo–Ca interaction is complex and highly cross-linked with the soil pH.
In general, Mo contents of plants, within the range of 0.1–0.5 mg/kg, are sufficient for their metabolism, whereas concentrations in the range of 10–50 mg/kg
are toxic to most plant species. Only some legumes and cruciferous plants require
more Mo.
Molybdenum concentrations in plants closely reflect its mobile pool in soils, as it
is readily taken up by plants, when present in soluble species. Molybdenum is always
more available from neutral and alkaline soils than from acidic ones. Some plants,
particularly legumes, may accumulate very high amounts of Mo, up to 350 mg/kg,
without toxicity symptoms.