POTASSIUM-TRANSPORT IN WHEAT SEEDLINGS GROWN WITH DIFFERENT POTASSIUM SUPPLIES .1. ION CONTENTS AND POTASSIUM INFLUX

Wheat seedlings (T. aestivum L. cv. Martonvasari 8) germinated and grown with different K+ supplies in a complete nutrient solution were examined. As controls, plants were grown in tridistilled water and 0.5 mmol/dm3 CaSO4 solution. The ionic states of the roots and shoots were followed from the 3rd to the 11th day after germination, with daily measurement of their K, Na, Mg and Ca contents. On the 11th day, the K+(86Rb) influx of the excised roots was determined in the presence or absence of Ca2+ in the uptake solution of 1 mmol/dm3 KCl. The water contents of the plants and the K, Na, Mg and Ca contents of excised roots were also measured before and after the uptake experiments of 1 h. The rate of growth of the seedlings was practically independent of the ionic supply during the first 6 days. By the 7th and 11th days all plants (even those grown in tridistilled water) had reached the 1-leaf and the 2-leaf stage, respectively, but the water content of the roots of the control plants (.apprx. 86%) was significantly lower than that of other plants (.apprx. 95%). The lowest K content of wheat roots can be estimated as .apprx. 200 .mu.mol (g dry weight)-1, which is .apprx. 10 .mu.mol (g fresh wt)-1. K seemed to be partly replaced by Na. At high K contents in the roots and shoots, Na and Mg are expelled from both and, Ca is expelled from the shoots. The Ca content of the roots seemed to be unaffected by the K+ supply (or K content). The K+(86Rb) uptake of excised roots is interpreted on the basis of the negative feedback regulation by the K content of the roots. A possible Ca2+-K+ exchange is also outlined.