Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

Nutrient Stress
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Molybdenum deficient plants are sensitive to low temperature stress and water logging
(Vunkova - Radeva et al., 1988). Molybdenum deficiency affects flowering and pollen
producing capacity. Pollen grain size and germination of pollen was also decreased
under molybdenum deficiency (Table 13).
Table 13. Effect of molybdenum on pollen production and
viability in maize plants*
Molybdenum Molybdenum No. of pollen Pollen Pollen
treatment content of pollen grains per diameter germination
(mg/kg) grains (µg/g dry wt) anther (µM) (%)
0.01 17 1300 68 27
0.10 61 1937 85 51
20 92 2437 94 86
*Adapted from Agarwala et al. (1979).
Molybdenum deficiency differs from species to species and also on the source
of nitrogen supply. The threshold deficiency levels of Mo vary between 0.1 and 1.0 µg/
g leaf dry weight (Bergmann, 1988). The visual symptoms are stunted growth and
chlorosis in young leaves. Dicots are relatively susceptible to Molybdenum deficiency
as compared to monocots. When Mo deficiency is severe, there will be a drastic reduction
in leaf size and the development of irregular leaf lamina in cauliflower and this is
commonly known as whiptail symptom. In molybdenum deficient bean plants, older
leaves exhibit necrosis of the chlorotic areas between the veins and leaf margins.
When the molybdenum content exceeds 50 µg/g dry weight, there is a possibility
of occurrence of Mo toxicity in many plants. Molybdenum toxicity induces the
malformation of the leaves and often develop a golden yellow discolouration of the
shoots due to the formation of molybdocatechol complexes. In potato and tomato the
Mo toxicity causes the development of reddish or golden yellow colour of the shoots.
Sulphate fertilization may reduce the molybdenum toxicity.
Many soils contain adequate levels of Mo to meet the requirement of crops.
Molybdenum deficiency is seen in acid sandy soils and in soils with high anion exchange
capacity. Legumes need more Mo to meet the demand of root nodule bacteria.
Among the vegetables, cabbage and cauliflower are known to have higher demand for
Mo. Molybdenum deficiency can be corrected by the foliar application of 100g NaMoO 4
/
hectare. Sometimes liming also prevents Mo deficiency. Foliar application of Mo is
beneficial as compared to soil application as evidenced by increase in the yield, nitrogen
uptake and Mo content in groundnut, grown in Mo-deficient soil (Table 14).