The Effect of Alar on Permeability, a Possible Explanation for its Mode of Translocation1,3

Autoradiographs of girdled and non-girdled almond seedlings treated with 14 C-Alar revealed that the growth retardant moved readily from the phloem to the xylem. Autoradiographs of comparable seedlings treated with 14 C-sucrose, with and without Alar pretreatment, showed that Alar induced greater leakage of radioactive material from the symplast to the apoplast indicating that the material lowered membrane integrity. This effect of Alar on cytoplasmic permeability was examined by immersing dormant stems, leaf discs, and beet root tissue in solutions of Alar and water. In all tissues, the compound induced greater leakage of cellular contents than water, which is attributed to the ability of Alar to depress utilization of respiratory energy necessary for the retention of solutes in the vacuole.