CONTROL OF POTASSIUM INFLUX IN ROOTS OF BIRCH (BETULA-PENDULA) SEEDLINGS EXPOSED TO CADMIUM

The nutrient status of the root may be a factor of vital importance for plant tolerance to changes in the environment. In this study the effect of Cd on the K+ uptake of birch plants, starved and non-starved of potassium, was examined. Changes in potassium influx of bitch (Betula pendula) roots, with time, were examined in birch plants introduced to a nutrient solution containing 125 mu M K+ after a K+-starvation period. Cadmium was introduced during the K+-recovery period and the effects of the heavy metal on the development of the uptake pattern was studied. When no Cd was present K+ influx, in previously K+-starved plants, increased with time and reached a maximum after 6 h. When 2 or 5 mu M Cd was supplied simultaneously with potassium to the root, K+ influx was unchanged during an 8 h K+-recovery period, and the K concentration in the roots did not increase as was the case when the plants were given K+ without Cd. In another experiment Cd supply (2 mu M) to K+-fed plants gave an immediate 50% decrease in K+ influx. However, after prolonged exposure to Cd (up to 20 h), K+ influx recovered to the control value.