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Interaction of Naphthaleneacetic acid and Kinetin in the Senescence of Detached Leaves ¹

Department of Vegetable Crops, University of California, Davis, California

Kinetin and naphthaleneacetic acid were applied separately and in combination to excised leaf disks, localized areas of laminae, and petioles of detached leaves of broccoli (Brassica oleracea L., var. italica) and Xanthium (Xanthium pensylvanicum Wallr.). Senscence (measured as loss of chlorophyll) was strongly retarded by kinetin, but very slightly influenced by naphthaleneacetic acid. When the 2 substances were applied concurrently, the effect of kinetin was markedly reduced by naphthalene acetic acid. Neither interference with uptake nor transport of kinetin appeared to cause the reduction.

In broccoli, the response to kinetin was as great in young leaves as in old leaves, and the reduction of the kinetin effect by naphthaleneacetic acid was greater in young leaves than in old leaves. Results indicate that the prevention of loss of critical material may be more significantly related to the delay of senescence by kinetin than is directed transport and accumulation (mobilization). Kinetin may control 2 or more events which contribute independently to the delay of senescence in detached leaves, and naphthaleneacetic acid may possibly interfere with only 1 of them.