MOVEMENT AND DISTRIBUTION OF 14C WITHIN PETIOLES OF INTACT COLEUS BLUMEI (LABIATAE) AFTER APPLICATION OF INDOLE-3-(ACETIC ACID-2-14C) TO THE LEAF SURFACE

Auxin transport and immobilization were followed in the petioles of intact plants of Coleus blumei Benth. after application of IAA-2-¹⁴C at a physiological concentration as droplets to the upper surface near the base of the blades of leaves #3 and #5. After 14 hr transportable and immobilized radiocarbon was found all along the petioles. Moreover, about half the total amount of ¹⁴C detected within the plant (= uptake) had moved beyond the petioles. This was true for leaves of both ages although the younger #3 petioles were only about half as long as the older #5 petioles. Because the uptake of radiocarbon by the #3 petioles was roughly half that of the #5 petioles, the absolute amounts immobilized per unit length of section were essentially uniform in the two petioles. On the contrary, the fractions remaining transportable within the #3 petiole sections averaged half those of the #5 petiole sections. The distribution of the transportable and the immobilized radioactive fractions along the petioles was characterized by high values near the apical application point, a decrease toward the middle of the petioles, and an increase to the level of the apical part toward the base of the petioles, which includes the abscission layer. The results have been discussed in connection with measurements of the cross sectional areas and the lengths of the epidermal and subepidermal cells along the petioles. An auxin transport and immobilization model, which assumes there are two different immobilization systems of different strength in the differently aged tissues, is outlined to explain the observations.