Zinc: Importance and Current situation

Zaghum Sattar & Abdul Saboor Butt

Institute of soil & Environmental Sciences, University of Agriculture, Faisalabad

Zinc (Zn) is among those minerals that were first considered as essential for plants, animals and human. Zn is a basic essential trace mineral element for normal healthy growth in plants, animals and humans that uptake as a divalent cation (Zn²⁺) by plants. Zn is playing principal metabolically role in plants and required in the carbonic enzyme present in all photosynthetic tissues, and also required for chlorophyll biosynthesis. Zinc is one of the essential micronutrient for the normal healthy growth and reproduction of crop plants. Zn plays an important role in plant metabolism by influencing the activities of enzymes, hydrogenase and carbonic anhydrase, stabilization of ribosomal fractions and also synthesis of cytochrome.  Zn also activate plant enzymes involved in carbohydrate metabolism, integrity maintenance of cellular membranes, synthesis of nucleic acids and specific proteins, regulate auxin synthesis and pollen formation. The regulation of the gene expression required for the tolerance of environmental stresses in plants also depend on the Zn.Zinc deficiency involves in the abnormalities development in plants as deficiency symptoms such as stunted growth, chlorosis and smaller leaves, spikelet sterility. Zn deficiency can also adversely affect the quality of harvested products; plants susceptibility to injury by high sunlight or temperature intensity and to infection by fungal diseases can also increase. A zinc deficiency affects the capacity for water uptake and transport in plants. Zn involves in the synthesis of tryptophan which is a precursor of IAA, and in the production of growth hormoneauxin. Zinc deficiency is common in humans, animals and plants. More than 30% world’s population suffers from Zn deficiency. Zinc deficiency is found to be more common in developing countries due to low Zn in their diet. Zinc plays a part.in the basic roles of. Cellular functions in all living organisms and also involved in the human immune system. The optimum dietary intake for human adults is 12-15 mg Zn per day. Zinc acts as a catalytic or structural component in various body enzymes.Unsatisfactory intake and improper absorption of Zinc in the body may cause deficiency of Zn.  Zn malnutrition in humans can result in many fatal and other diseases like hair and memory loss, skin problems and weakness in eye side and body muscles. Insufficient intake of Zn during pregnancy in women also causes stunted brain development of the fetus. Infertility has also been observed in Zn deficient men. Zinc deficiency may cause congenital diseases like Acrodermatitis enteropathica. According to FAO/WHO recommendations an average male need 11 mg of Zn daily while an average female needs 9 mg of Zn. During pregnancy and lactation, the female needs 13 mg to 14 mg of Zn daily. Infants from 7 months to 3 years need 3 mg, 4 to 8 years need 5 mg and children from 9 to 13 years need 8 mg of Zn daily. In Pakistan, Zn deficiency is common in children and in women.Trace elements such as Zn are contained in all soils in measurable amounts. However, these concentrations can vary considerably. The overall mean total Zn concentration in soil is around 55 mg Zn kg^-1. A typical range of Zn in soils is from 10 to 300 mg Zn kg^-1. These values do not include contaminated soils, which may have much higher zinc concentrations.However, plant available Zn is very low as compared to its total amount. For a better Zn nutrition of human beings, cereal grain should contain around 40-60 mg Zn kg^-1 where current situation is 10-30 mg Zn kg^-1. Soils with low zinc availability for plant uptake represent nearly half of the cereal-growing areas of the world. The countries most affected by zinc deficient soils are Pakistan, India, Iran, China and Turkey with 50-70% of arable land classified as zinc deficient.