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

202
K. Janardhan Reddy
Table 12 .
Effect of copper deficiency on flowering and certain enzyme activities
In Chrysanthemum morifolium*
Treatment Copper content No. of Enzyme activity
(mg/g leaf flowering (relative)
dry wt) shoots / Polyphenol IAA Peroxidase
plant oxidase oxidase
Cu deficient 2.4 8 26 52 41
Cu sufficient 7.9 14 100 100 100
*Adapted from Davies et al. (1978).
The critical deficiency range of copper is about 1-5mg /g dry matter depending
on plant species and growth stage and nitrogen supply (Thiel and Finck, 1973). In
cereals, the deficiency symptoms first appear in the leaf tips at tillering stage. The leaf
tips become white and leaves will be narrow and twisted. Plants show stunted growth
in severe deficient conditions. Die back disease in citrus is very well documented.
Legumes and tomato show interveinal chlorosis and distortion of the lamina.
Many crop plants show toxicity if the leaf tissue contains above 20 - 30 mg.
Young leaves show interveinal chlorosis, while old leaves develop reddish orange or
pink colouration and rolling of the leaf margins due to the loss of turgor. Later on, these
leaves become dried and withered. Under severe toxicity, roots turn reddish brown and
necrotic.
Foliar application of copper in the form of CuSO 4
or chelates are recommended
to correct the copper deficiency in crops. Selection of genotypes which are efficient in
high uptake of copper with more translocation efficiency from roots to shoots is another
solution.
12. MOLYBDENUM
Molyndenum (Mo) is the only period five transition element required by plants in the
form of molybdate oxyanion (MoO 4
2-
). The total Mo content in most soils varies from
0.60 to 3.50 ppm. The available content is about 0.2 ppm. Molybdenum is required by
plants in small quantities as compared to other elements except nickel.
Molybdenum is a constituent of nitrate reductase, nitrogenase, xanthine oxidase
and sulphate oxidase. It plays a structural and catalytic role in these enzymes.
Molybdenum is closely related to nitrogen metabolism and the requirement of Molybdenum
depends on nitrogen source. Molybdenum deficient plants had shown higher
activity of ribonuclease and lower activity of alanine transferase. Molybdenum deficiency
induces the accumulation of organic acids and amino acids. Molybdenum deficient
mustard leaves contained low levels of DNA and RNA (Chatterjee et al., 1985).