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

Nutrient Stress
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Iron toxicity is mainly found in water logged soils and under flooded conditions.
Iron toxicity may cause bronzing, stunted top and root growth.
Mulberry (Morus alba L) plants have shown increased dry matter yield upto
50.0 µM and a yield reduction was observed at 100.0 µM when grown in solution
culture (Table 7).
Table 7. Effect of ir on on dry matter yield and
iron content in Morus alba L.var.kanva-2*
Iron supply leaves (µM) Dry matter yield (g plant -1 ) Iron content in young
( µg g -1 dry weight)
0 36.84 ± 1.45 110.39±7.50
5.0 36.47±4.55 120.13±5.62
50.0 86.77±5.72 146.10 ±3.75
100.0 70.90±2.05 137.98 ±0.94
*Adapted from Tewari (2004).
Iron content in plant tissues is about 100 ppm of dry matter. Most of the
agricultural crops require < 0.5 ppm in the soil in the plough layer where as total iron is
about 2% or 20,000 ppm in the soil. The formation of iron-organic complexes, the chelates
play vital role in supply of iron from soil to plants. Siderophores are recognized as the
most important organic molecules which combine with iron and make it available to
plants and microbes (Brown et al,. 1991).
9. MANGANESE
The soil content of manganese (Mn 2+ ) varies between 200 and 300 ppm. Availability of
Mn 2+ to plants depend on soil pH, microbial activity and soil water. The uptake of Mn
is mainly suppressed by high levels of Fe, Zn and Cu.
Manganese is mainly associated with photosynthesis, redox processes and
hydrolytic reactions. It forms strong complexes with biological ligands and participates
in substrate-enzyme interactions of intermediary metabolism. In many biochemical
functions Mn 2+ resembles Mg 2+ . Manganese can replace Mg 2+ in many of the
phosphorylating and group transfer reactions. Although there are several enzymes
which are activated my Mn but mainly two Mn containing enzymes have been studied
in detail. The first one is a manganoprotein – photosystem II of photosynthesis and the
other one is superoxide dismutase (Elstner, 1982). Manganese activates several enzymes
involved in the biosynthesis of some aromatic amino acids and certain secondary
metabolites like lignin and flavonoids (Burnell, 1988).