Distribution of internal secretory structures in Tagetes patula (Asteraceae)

Seedlings and flowering plants of Tagetes patula present secretory reservoirs similat to many other Asteraceae which produce polyacetylenes. These polyacetylene reservoirs (PRs) that contain both thiophene and essential oils, show a blue-yellow fluorescence and a red colour when observed in the UV and conventional microscope respectively. In the root of the seedlings two arrays of six PRs arise abutting on the endodermis. PRs of branch roots are connected to those in the parent roots. A single layer of "epithelial" non-specialised cells forms the secretory tissue. In the hypocotyl four PRs, characterised by a uniseriate epithelium, arise in the cortex in front of the vascular bundles. In the epicotyl, instead, we found eight PRs localised between the vascular bundles. In the cotyledons, in the leaves and in the flower bracts there are only secretory cavities. In the flowering plant, PRs also occur in the corolla of the tubular and ligulate flowers of the inflorescence, with a typically biseriate epithelium.