The Influence of Dwarfing Interstocks on the Distribution and Metabolism of Xylem-Applied [3H]Gibberellin A4 in Apple

Abstract

The influence of an interstock of the dwarfing cultivar M9 and the nondwarfing cultivar MM115 on the distribution and metabolism of labeled gibberellic acid A4 ([3H]GA4) of high specific radioactivity (5.18 .times. 1010 becquerel per millimole) applied to the xylem of the rootstock in grafted apple (Malus .times. domestica Borkh.) trees was compared. Free [3H]GA-like metabolites of [3H]GA4, including putative GA1, GA2, GA8, and GA34, as well as various 3H-putative GA glucosyl conjugates were detected in stem segments from both cultivars. M9 interstocks reduced the total uptake of [3H]GA4 and decreased the proportion of 3H metabolites transported to the shoots and leaves of scions. The M9 interstock tissue and adjacent rootstock and scion tissue retained a much greater amount and a higher proportion of the label than did comparable tissue of the nondwarfing MM115 interstock. In addition, the amount and proportion of free [3H]GAs was higher, and the proportion of putative [3H]GA glucosyl conjugates lower, in M9 interstocks compared to MM115. These effects of the dwarfing interstock on GA distribution and metabolism indicate a significant role for GAs in any satisfactory explanation of the dwarfing mechanism in apple.