MOVEMENT OF WATER AND SOLUTES IN SIEVE TUBES OF WILLOW IN RESPONSE TO PUNCTURE BY APHID STYLETS . EVIDENCE AGAINST A MASS FLOW OF SOLUTION

Experiments are described in which bark strips of willow were sealed to polythene tubes having two compartments. This allowed investigations to be made of the transport along the sieve tubes of tritiated water, 14C‐labelled sugars, and 32P‐phosphates from one compartment, towards a stylet situated in the bark over the other compartment. Although activity from both 14C and 32p was detected in the stylet exudate usually within 1 hour from isotope application, tritium activity was never detected even after a period of 8 hours in most experiments, though in certain cases, very low activities were detected after 4 hours. Subsequent experiments in which stylets were sited over both compartments showed that tritium activity moved laterally into the punctured sieve element more rapidly than either 14C or 32P. Experiments using both live and dead bark in which stylets were not employed, showed that within 4 hours tritium activity had moved by diffusion along the whole length of a bark strip, therefore after this time tritium activity could have moved into the stylet exudate by a diffusional process. The lack of rapid longitudinal movement of tritiated water along the sieve tubes, indicates that the transport process is unlikely to be a mass flow of solution. Copyright © 1969, Wiley Blackwell. All rights reserved