ACTIVE PARTICIPATION OF THE ROOT SHOOT TRANSITION REGION TREATED WITHTRIIODOBENZOIC ACID IN BASIPETAL TRANSPORT OF C-14 INDOLE-3-ACETIC-ACID AND ETHYLENE EVOLUTION IN THE STEM OF APPLE SEEDLINGS

Treatment with triiodobenzoic acid (TIBA) in lanolin to the root colla r of I-year-old apple seedlings cultivar 'Antonovka' 6 days before C-1 4-indole-3-acetic acid (C-14-1-IAA) application reduced by half the di stance of C-14 basipetal transport compared with that of the controls (treated with lanolin only). The longer the time interval between TIBA and C-14-1-IAA application the more restricted was auxin transport. T he mid-stem application of TIBA did not limit basipetal transport of C -14 which reached, similar to controls, the point of the TIBA treatmen t within 24 h. In a parallel experiment with leafy seedlings, a high r ate of ethylene evolution was observed in the youngest parts of stems of plants in which TIBA had been applied to the root collar, The total amount of ethylene evolved from the uppermost part of the seedlings i ncreased significantly within 7-14 days after TIBA application to the root collar. This phenomenon was accompanied by a significant decrease in dark leaf respiration. It is suggested that TIBA application to th e root collar but not to the mid-stem, restricts auxin transport from the apex, and causes a partial auxin depletion leading to a temporary cessation of shoot growth that favours acceleration of generative proc esses.