Correlative aging and transport of P(32) in corn leaves under the influence of kinetin

1. The course of senescence in leaves of corn seedlings, as measured by the loss of chlorophyll, is shown to be controlled by two correlative influences: a) In the isolated leaf, the base tends to enhance yellowing of the tip region. b) In the leaf attached to the intact plant, correlative aging is delayed by interactions with other parts of the plant. 2. Transport of P(32) in the isolated leaf is directed from tip to base. It is promoted under conditions enhancing senescence of the tip (application of kinetin to the base). Conditions delaying senescence (leaf attached to intact plant) defer the basipetal P(32)-transport. This suggests that the pattern of correlative aging in detached leaves is caused by a shift of materials from tip to base ("directed transport" or "mobilization"). 3. Kinetin-induced directed transport of P(32) was used as a test system to study mobilization. Localized application of kinetin to a leaf causes a) an accumulation of translocated P(32) in the treated area, b) an acceleration of P(32)-transport directed towards the kinetin center. 4. The rate of kinetin-induced P(32)-transport is shown to be mainly determined by the activity of the mobilizing center; but the dissipation of phosphates out of the source region, being a separate variable, may also influence the rate of P(32)-transport. 5. The attracting activity of mobilizing centers is shown to be enhanced by increasing amounts of materials already accumulated. Thus, mobilization is a self-amplifying process. This is also reflected in the sigmoid shape of the time curves of P(32)-mobilization.