UPTAKE AND PHYSIOLOGICAL-EFFECTS OF CADMIUM IN SUGAR-BEET (BETA-VULGARIS) RELATED TO MINERAL PROVISION

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, 5.0 or 20.0-mu-mol) 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.