Deficiencies of micronutrients have increased in some crop plants due to increases in nutritional demands from high yields, use of high analysis (N, P, K) fertilizers with low micronutrient quantities, and decreased use of animal manure applications (40). Copper deficiency symptoms appear to be species-specific and often depend on the stage of deficiency (7). Reuther and Labanauskas (7) give a comprehensive description of deficiency symptoms for 36 crops, and readers are encouraged to consult this reference. In general, the terminal growing points of most plants begin to show deficiency symptoms first, a result of immobility of copper in plants. Most plants will exhibit rosetting, necrotic spotting, leaf distortion, and terminal dieback (7,33). Many plants also will show a lack of turgor and discoloration of certain tissues (7,33). Copper deficiency symptoms in lentil, faba bean, chickpea, and wheat (Triticum aestivum L.) were chlorosis, stunted growth, twisted young leaves and withered leaf tips, and a general wilting despite adequate water supply (33).
Copper deficiency limits the activity of many plant enzymes, including ascorbate oxidase, phe-nolase, cytochrome oxidase, diamine oxidase, plastocyanin, and superoxide dismutase (63). Oxidation-reduction cycling between Cu(I) and Cu(II) oxidation states is required during single electron transfer reactions in copper-containing enzymes and proteins (64). Narrow-leaf lupins (Lupinus angustifolius L.) exhibited suppressed superoxide dismutase, manganese-superoxide dis-mutase, and copper/zinc-superoxide dismutase activity on a fresh weight basis under copper deficiency 24 days after sowing (65). Copper deficiency also depresses carbon dioxide fixation, electron transport, and thylakoid prenyl lipid synthesis relative to plants receiving full nutrition (66).
In brown, red, and green algae, the most severe damage in response to Cu2+ deficiency was a decrease in respiration, whereas oxygen production was much less affected (67).
Plants differ in their susceptibility to copper deficiency with wheat (Triticum aestivum L.), oats, sudangrass (Sorghum sudanense Stapf.), and alfalfa being highly sensitive; and barley, corn, and sugar beet being moderately sensitive. Copper tissues levels below 2mg kg1 are generally inadequate for plants (9). A critical copper concentration for Canadian prairie soils for cereal crops production was reported as 0.4 mg kg-1 (42).
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