PH AFFECTS 1H-INDOLE-3-BUTYRIC ACID UPTAKE BUT NOT METABOLISM DURING THE INITIATION PHASE OF ADVENTITIOUS ROOT INDUCTION IN APPLE MICROCUTTINGS

The influence of root initiation medium pH on root formation was inves tigated in relation to uptake and metabolism of applied IBA in microcu ttings of Malus xdomestica Borkh, 'Gala' and 'Triple Red Delicious', R oot formation and uptake of H-3-IBA were related inversely to root ini tiation medium pH. Maximum root count (10.3 roots) and IBA uptake were observed at pH 4.0, Regardless of pH, overall root count of 'Gala' wa s higher (13.5 roots) than 'Triple Red Delicious' (4 roots), Uptake of IBA was highest at pH 4.0 for 'Gala' (1.7% uptake) and at pH 4 and 5 for 'Triple Red Delicious' (0.75% uptake), Metabolism of IBA. was the same regardless of root initiation medium pH or cultivar examined, One -half of the IBA taken up was converted to a compound that coeluted wi th IBAsp during high-performance liquid chromatography. Apparently, pH regulates root formation by affecting IBA uptake but not metabolism, The level of auxin in tissue appeared unrelated to root formation betw een genotypes. Chemical names used: 1H-indole-3-butyric acid (IBA); 5- H-3-indole-3-butyric acid (H-3-IBA); indole-3-butrylaspartic: acid (IB Asp).