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

208
K. Janardhan Reddy
Table 17.
Content of Nickel and certain micronutrients in shoots and
seeds of Lupin and Rye (µg/g dry wt.)*
Plant Part Ni Fe Mn Zn Cu Mo
Lupin Shoots 0.81 178 298 28 3.6 0.08
Seeds 5.53 47 49 41 6.0 3.29
Rye Shoots 0.62 78 16 07 1.6 0.17
Seeds 0.28 26 27 25 4.4 0.33
*Adapted from Horak (1985a).
Crop plants are invariably subjected to nickel toxicity, when they are treated
with sewage sludge. Critical toxicity levels are in the range of 10 µg/g in sensitive and
50 µg/g dry matter in tolerant plants (Asher, 1991). Plants suffering with nickel toxicity
show necrosis on the leaf tips and margins. Young leaves may become severely distorted
and the terminal shoot buds may die.
16. ENVIRONMENTAL ASPECTS OF MINERAL NUTRITION
Organisms are subjected to various environmental stresses. They try to adopt to these
conditions for their physiological needs. Plants mainly depend on root system to acquire
most of the mineral elements for growth and development. Roots are associated
with variety of soil conditions ranging from arid to moist environment, different degrees
of microbial activity and kinds of nutrient availability from acidic to basic. Plants are
growing in a variety of soils where the pH of the soil solution may vary from extreme
acidic conditions to alkaline situations.
About 50% of the world’s arable land is acidic (Kochian et al., 2004). Aluminium
(Al) availability increases in acid soils (< pH 5.5). Aluminium is one of the most
abundant elements and constitutes about 8% of the earth’s crust. Aluminium toxicity is
an important growth-limiting factor for many plants. Detailed investigations have been
carried out on the Al tolerance and toxicity in certain plants (Woolhouse, 1983). The
primary target of Al toxicity is root growth, which is inhibited more than shoot growth
(Fox, 1979). Root tips and lateral roots become thickened and turn brown. Al toxicity
symptoms resemble phosphorus deficiency symptoms like stunted growth with dark
green leaves, and yellowing and death of leaf tips. Al may interfere with phosphorus
uptake and metabolism. At higher levels, aluminium induces Ca 2+ and Mg 2+ deficiency.
Liming of acid soils decrease the risk of Al induced Ca 2+ and Mg 2+ deficiency and
inhibition of root growth. Large number of plants in acid soils are adapted to Al toxicity.
Foy (1974, 1975) found that certain cultivars of wheat, barley and soybean resisted Al