The lag‐phase of potassium translocation from the root to the shoot of low‐salt barley plants. Kinetic and localization studies

In roots of low‐salt barley (Hordeum vulgare L.), translocation of K+, as well as of several other ions, from the root to the shoot starts after a lag‐time. Its length is independent of external concentration. The onset of upward translocation can be remarkably abrupt. Three hypotheses that could explain the lag‐phase were tested: It is the result of successive loading of the concentric root cell layers centripetally from the epidermis. It is the result of successive loading of the root basipetally from the apex. It is the result of induction of the mechanism(s) responsible for upward translocation. All three hypotheses are rejected. Within the whole root radial as well as longitudinal equilibration appears to be very rapid. The simple model of compartmentation is rejected. A more complex compartmentation of the cytoplasm (symplasm) in which the endopiasmic reticulum could play a predominant role is suggested. The mechanisms of vacuolar accumulation and upward translocation appear biochemically related.