Abstract
Zinc is an essential element for photosynthesis and its deficiency may play a role in the reduction of activity of rubisco and hence decreased rate of photosynthesis in higher plants. Zinc deficiency sometimes resembles Fe/Mn deficiencies. Under severe zinc deficiency the shoot apices die ('die-back') as is widely distributed. Zinc toxicity leads to chlorosis in young leaves. Induced manganese deficiency might also be of importance as high zinc supply strongly decreases the manganese content of plants. Most preventing measures for zinc deficiency are selection of Zn efficient variety that is tolerant to high level of bicarbonate as well as low zinc in soil. Curative measure for correcting are application of 20-25 kg/ha ZnSo4 in acid soil, 22 kg Zn/ha initially followed by 5-10 kg Zn in the later years or 50% gypsum + 10 t GM + 22 kg Zn once in 2-3 years in sodic soils, 1.0-1.5 kg/ha Zn as foliar spray at tillering stage and 2 times latter is very helpful for correct this deficiency. Zinc is very tightly bound to phytic acid and the formation of protein-zinc-phytic acid complexes increases the resistance to hydrolysis that leads to decrease in bioavailability of Zn to human and animals. Enrichment of cereal grains with Zn through both genetic (e.g., breeding) and agronomic (e.g., application of Zn fertilizers) biofortification is a high priority area of research, and will contribute to minimizing Zn-deficiency-related health problems in human populations.
Highlights
Due to increase availability of Ca, Mg, Cu, Fe, Mn and P under prolonged submergence Zn availability and uptake hampered by the crops.Zinc is an important plant micronutrient for crop growth and higher production
Zinc is an essential element for photosynthesis and its deficiency may play a role in the reduction of activity of rubisco and decreased rate of photosynthesis in higher plants [3]
In enzymes with catalytic zinc functions the zinc atom is coordinated to four ligands, there of which are amino acids, with histidine (His) being the most frequent, followed by glutamine (Glu) and asparagine (Asp); a water molecule is the fourth ligand at all catalytical sites [4].In enzymes with structural zinc functions the structural zinc atoms are coordinated to the S-groups of four cysteine residues forming a tertiary structure of high stability [5]
Summary
In enzymes zinc has three functions; catalytic, cocatalytic (coactive), or structural. In enzymes with catalytic zinc functions (e.g., carbonic anhydrase and carboxypeptidase) the zinc atom is coordinated to four ligands, there of which are amino acids, with histidine (His) being the most frequent, followed by glutamine (Glu) and. Asparagine (Asp); a water molecule is the fourth ligand at all catalytical sites [4].In enzymes with structural zinc functions (e.g., alcohol dehydrogenase, and the proteins involved in DNA replication and gene expression) the structural zinc atoms are coordinated to the S-groups of four cysteine residues forming a tertiary structure of high stability [5]. Most of the zinc-enzymes have only one zinc atom per molecule, the alcohol dehydrogenase being an exception
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