Distribution of Two Major Iridoids in Different Organs of Antirrhinum majus L. at Selected Stages of Development

Two iridoid glucosides isolated from leaves of Antirrhinum majus L. were identified as the known compounds antirrhinoside and antirrhide. Plants grown hydroponically demonstrated that antirrhinoside is present in all plant organs including the roots. In contrast, antirrhide is found only in leaves. Furthermore, both iridoids were identified in the main stem axillary leaves and leaves on the lateral branches. The highest concentrations of antirrhinoside were found in the main and lateral stems as well as the buds and flowers. As leaves age, for both cultivars, the levels of antirrhinoside drop significantly, and there is a corresponding increase in antirrhide. In spite of the different genetic backgrounds of the two cultivars, the overall distribution of the iridoids was similar during vegetative and flowering development. Radiolabeling of recently expanded axillary leaves with ¹⁴CO₂ showed that both antirrhinoside and antirrhide were prominently labeled in the laminar tissue. However, only ¹⁴C-antirrhinoside was recovered in the subtending petiole tissue, consistent with the suggestion that it is a phloem mobile compound.