Effects of Ca2+ and Cd2+ on the Carbohydrate Metabolism in Sugar Beet (Beta vulgaris)

Sugar beet (Beta vulgaris L. cv. Monohill) were cultivated ina nutrient solution with different combinations of Ca²⁺ (36,180, 720 or 3560µM) and Cd²⁺ (0, 1, 5 or 20µM).The dry and fresh weights, the content of Ca²⁺ and Cd²⁺ , sucrose,fructose, glucose and starch in 5-week-old plants was analysedas well as the rate of [¹⁴C]-sucrose uptake in discs from 3-month-oldstorage roots. The carbohydrate metabolism was indirectly affectedby the presence of calcium or cadmium. Cadmium caused a diminisheddry weight and carbohydrate concentration. The dry weight wasunaffected by the Ca²⁺ level but the carbohydrate distributionbetween storage and growth processes was affected; at low Ca²⁺in the tissue, the growth was retarded and the level of storagecarbohydrate increased, while at high Ca²⁺ the opposite wasfound. The [¹⁴C]-sucrose uptake decreased in tap roots cultivatedat low Ca²⁺ . Long term exposure to Cd²⁺ also decreased thesucrose uptake in tap roots. Direct Cd²⁺ addition to the assaymedium, however, increased the sucrose uptake, probably at thetonoplast, while Ca²⁺ had no transient effect on the uptake.Cadmium increased the Ca²⁺ concentration in the plant, but Ca²⁺did not affect the net-uptake of Cd²⁺. Key words: Sugar beet, cadmium uptake, calcium uptake, carbohydrate formation, growth