The mechanism of kinetin-induced transport in corn leaves

1. Kinetin-induced transport of P(32) in detached corn leaves is shown to be limited to the axial direction of the leaves, i.e. along the axis of the vascular bundles. It is not apparently dependent on the water flow in the xylem, and it can be blocked by steam-killed zones or by metabolic inhibitors. It is concluded that kinetin-induced redistribution of phosphates in isolated corn leaves takes place in the phloem. 2. The movement of P(32) is preferentially toward the base of the excised leaf, indicating a natural mobilization center at the leaf base. 3. Kinetin treated parts of leaves attract and accumulate P(32). They do not accumulate the radioisotopes Na(22), Rb(86), Cl(36) and I(131); but the transport of Na(22) directed towards kinetin centers is enhanced. 4. Two "mobilizing centers" established by kinetin application along the leaf axis do not attract P(32) from intermediate tissue at the same time in opposite directions. They compete with each other for the transport system: both the direction and the velocity of movement are determined by the difference of the "mobilizing forces". Thus, mobilization is either to one or to the other mobilizing center. 5. Under conditions of enhanced transport (i.e. in presence of kinetin centers), the distribution curves of P(32) and Na(22) are flattened. This change would be expected for the mass-flow type of transport. 6. It is concluded that "mobilizing centers" in isolated corn leaves stimulate a mass-flow transport in the phloem. Evidence is presented that they act as suction pumps. Some general aspects of phloem transport are discussed.