THE ABSORPTION OF L-α-ALANINE AND L-α-AMINO-ISO-BUTYRIC ACID DURING THEIR MOVEMENT THROUGH THE XYLEM VESSELS OF TOMATO STEM SEGMENTS

Two labelled amino acids (1 ml, 0.005 M), L-α-alanine and L-α-amino-iso-butyric acid were allowed to perfuse separately through isolated stem segments of about 12 cm length. After a rapidly increasing initial absorption a steady-state absorption was established, from which for each amino acid the fractional rate of escape per unit stem length could be calculated (*K in mm−1). The values found could be confirmed by measuring the radioactivity in one-cm pieces of the stem segment used. *K-alanine was found to be about 8 × *K-α-amino-iso-butyric acid. Influences of transpiration and flow rate through the xylem vessels on the *K-values could be demonstrated. A provisional model for amino acid absorption from the xylem vessel is presented.