Influence of the root tip and the duration of washing on K+ [potassium] retention by excised apical root segments of corn

Excised apical segments of corn root (Zea mays) (5-15 mm from the root cap), some with and some without the root tips (0-5 mm) attached, were washed for varying time periods up to 4 hours in 0.5 mM CaSO4. After washing, tips were removed from those segments washed with tips attached, and then all segments and tips were analyzed for K+ content. The root tips (0-5 mm) initially contained about twice the K+ of the apical segments (5-15 mm). The loss of K+ did not exceed 15% in the tips or 20% in the apical segments. Loss of K+ was most pronounced during the 1st hour of washing. There was little difference in K+ content of apical segments washed with tips attached compared with those washed tipless. Thus, the presence of the intact root tip had no consistent influence on the ability of the older root tissue to retain K+.