Some Aspects of Translocation in Root Nodule Plants

Abstract

By the use of ¹⁶ N it is shown that the removal, over a short zone at the base of the shoot of a typical root nodule plant (alder), of the tissues external to the xylem does not interfere with the upward movement of fixed nitrogen from the nodules into the shoot. It is concluded that the fixed nitrogen, which is probably in organic form, can be translocated in the xylem in the transpiration stream, and that this is most likely its normal route. It is also shown that in unringed plants substantial enrichment in fixed ¹⁶ N is detectable in the shoot within 6 hours from the commencement of the exposure of the nodules to excess free ¹⁶ N. Structural and experimental evidence shows that the alder nodule is not a water-absorbing organ, and the mechanism of transfer of fixed nitrogen from the nodule into the transpiration stream is not obvious.