0I417SS 



leaf tissue (Smith and Brennan 1983). Other researchers have 

 reported both interference and enhancement of zinc uptake by 

 cadmium in different plants and at varying levels of cadmium 

 concentration (Hinesly et al. 1982, Pepper et al. 1983, Chaney et 

 al. 1976). Gerritse et al . (1983) found that increasing zinc in 

 the soil solution apparently increased cadmium uptake at high 

 solution concentrations of cadmium and decreased uptake at low 

 solution concentractions . Air pollution (as ozone) may interact 

 synergistically with cadmium to reduce crop yields, causing ozone 

 toxicity symptoms to develop at cadmium levels that normally would 

 be harmless (Czuba and Ormrod 1974). Hovmand et al . (1983) 

 reported that atmospheric cadmium accounted for 20 to 60 percent 

 of the total amount of cadmium in some agricultural crops in 

 Denmark . 



More than 70 percent of the total amount of cadmium in tree 

 leaves near a zinc smelter was found to be associated with the 

 cell wall. The remaining cadmium was distributed among the 

 cytosol , vacuole sap and cell organelles (Ernst, 1980) . Such a 

 compar tmentali zation of cadmium in cell walls may protect the more 

 susceptible metabolic sites of the cell. Cadmium content in cell 

 organelles is related to their function and potential for ion 

 uptake. For example, chloroplasts will accumulate much more 

 cadmium than mitochondria. 



Lee et al . (1976) found that cadmium may either stimulate or 

 inhibit a large number of plant enzyme systems, which may cause 

 subsequent biochemical chain reactions. Enzyme inhibition has 

 been shown to be the result of cadmium affinity for sulfhydryl 

 groups. Such disruption of enzyme systems has been shown to 

 affect nitrate uptake in corn seedlings and amino group catalysis 

 and nitrogen fixation by legumes (Mathys 1975, Volk and Jackson 

 1973, Huang et al. 1974). 



Cadmium may also negatively affect photosynthesis. It has 

 often been associated with reduced chlorophyll content, possibly 

 due to interference with the biosynthesis of photosynthetic 

 pigments and biomembranes . Enzymes needed for catalytic activity 

 may also be inactivated by cadmium because cadmium will bind with 



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