Sugar beet seedlings (Beta vulgaris L. cv. Monohill) were grown for 14 d on a nutrient solution based on the nutrient proportions in healthy plants. Nutrients were supplied either once at relatively high concentrations, or in small amounts with a daily incremental increase of 0·15 or 0·20 in accordance with an exponential growth rate. Cadmium (0, 0·6, 2·3, 50 or 20·0 μmol) was introduced either by a single addition or in daily increments of 0·15 or 0·20. Cadmium uptake, expressed as a percentage of total Cd2+ supplied, decreased with increasing total Cd2+ content and with decreasing availability of nutrients. With a daily supply of cadmium, net uptake, transport and content per unit of dry weight in roots and shoots were related to the total Cd2+ supplied. Cadmium caused growth retardation, increased root/whole-plant ratio, and decreased root-tip respiration and photosynthesis. At high initial nutrient concentrations, Cd2+ decreased the contents of sucrose, glucose, fructose, and starch per unit of dry weight. The opposite was found if nutrients were added daily. In the latter case, the dry weight/fresh weight ratio also increased. The effects of cadmium were related to [Cd2+] in proportion both to the root absorption area and to the nutrient concentration.
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Greger et al. (1991) studied this question.
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