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

188
K. Janardhan Reddy
constitution of the plant, chemical constituents of the soil, climatic conditions and age
of the plant. Despite wide variation in the mineral composition of different plants, a
certain critical level of nutrients is necessary for healthy growth of plants. An idea of
elemental composition with relative levels of each of the nutrients for higher plants is
indicated in Table 1.
Table 1. Concentration of mineral elements in soil, available form and their
content in plants*
Element Available form Content in soil Content in dry
matter (µmol/g)
Molybdenum
2-
MoO 4
0.2 – 2.0 ppm 0.001
Nickel Ni 2+ < 100 ppm 0.001
Copper Cu + & Cu 2+ 5 – 50 ppm 0.10
Zinc Zn 2+ 10 – 30 ppm 0.30
Manganese Mn 2+ 200 – 300 ppm 1.00
Iron Fe 2+ & Fe 3+ 2,50,000 ppm 2.00
Boron BO 3
20 – 200 ppm 2.00
Chlorine Cl - 3.00
Sulphur
2-
SO 4
0.04% 30
Phosphorus H 2
PO 4- 0.1% 60
Magnesium Mg 2+ 0.05% 80
Calcium Ca 2+ 0.5% 125
Potassium K + 2.0% 250
Nitrogen
+
NO 3-
& NH 4
1000
*Adapted from Epstein (1965), Brown et al. (1987), Hopkins and Hüner (2004).
Nutrient stress is a complex phenomenon, understanding of which requires
the co-ordinated efforts of soil scientists, ecologists, physiologists, biochemists,
agronomists and molecular biologists. Nutrient stress may result from either by low
levels of availability of the element or by the presence of excess concentrations. In
some cases the presence of one element in excess concentrations may induce the
deficiency of another element. In this context, attempts were made to show the availability,
functional aspects, and deficiency and toxicity symptoms of 14 elements essential for
the survival of plants and other elements, which produce phytotoxicity. Visual deficiency
symptoms provide a valuable basis for assessing the nutritional status of the plant.
Deficiency symptoms are the consequence of metabolic disturbances at various stages