Alteration of hormonal levels and hormone sensitivity by Ri T-DNA-transformation of apple cuttings

Abstract

Summary Changes in hormone levels and sensitivity to hormones were studied in the apple rootstock M 26 and in the clone transformed by Agrobacterium rhizogenes strain A4. The transformation of apple microcuttings by insertion of both TL-DNA and TR-DNA led to changes in leaf levels of all plant hormones studied (auxin, cytokinins and abscisic acid). An important increase in auxin and a decrease in cytokinin levels were observed. The ABA level was substantially lowered by transformation, whatever the water status of the leaves. The sensitivity to hormones of both transformed and untransformed cuttings was compared on the basis of their root induction efficiency. No significant difference in auxin sensitivity could be observed on this long-term response. However, the transgenic clone was less sensitive to cytokinin-induced rooting inhibition and more sensitive to ABA-induced rooting inhibition than the untransformed clone. The consequences of the changes in both hormone levels and sensitivity to hormones are discussed.