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Development and Growth Regulation

Hydroxylation of N⁶-(²-Isopentenyl)adenine to Zeatin

Relative Activities of Organ Systems from Actinidia arguta

Arnold Arboretum, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138

By incubating explants from Actinidia arguta seedlings on a nutrient medium supplemented with 20 to 30 micromolar N⁶-(²-isopentenyl)adenine (i⁶Ade) and then measuring zeatin (io⁶Ade) accumulation in tissues, the distribution of i⁶Ade hydroxylase activities in whole plants could be determined. Based on analyses with three entire plants, it is estimated that, as an organ system, roots contain approximately 68% of the plant's hydroxylase, while stems and leaves account for about 26% and 6%, respectively, of the total activity. Depending on the part of the root examined, hydroxylase activities ranged from 20 to 148 nanomoles io⁶Ade accumulated per gram fresh weight per 24 hours of incubation. Stem activities ranged from 17 to 165 nanomoles per gram fresh weight per 24 hours with the lowest activities being found at the tip. Leaf activities were substantially lower (1-10 nanomoles per leaf depending on position) than either root or stem.