THE LEVEL OF INDOLEACETIC-ACID IN THE LEAF OF CUCUMIS-SATIVUS AFTER DECAPITATION - ROLE OF PHOTOSYNTHESIS

Decapitation effects on the time-changes in indoleacetic acid (IAA) le vel were studied in a source leaf of a growing cucumber plant (Cucumis sativus L.). IAA content significantly decreased (by 25% as compared to the intact plants) after 12 to 24 h following decapitation, with th e simultaneous depression of the assimilate transport from the leaf. W eaker activity and accelerated senescence of the source leaf were asso ciated with a steady decline in the IAA content of the leaf. At the sa me time, decapitation activated the shikimate pathway of IAA biosynthe sis as manifested by leaf auxin labeling from (CO2)-C-14 in the light. A significant decline in the bound IAA level was also noted, suggesti ng that a free functionally active IAA might be released from its conj ugates. The homeostatic control of the IAA level in the source leaf an d the auxin role in the sink-source interrelations are discussed.