Secretory tissue ultrastructure in Tagetes patula L. (Asteraceae) and thiophene localization through X-ray microanalysis

Transmission electron microscopy has been used to determine the ultrastructure of secretory tissues in seedlings (10 days old plants) and in flowering plants (50 days old plants) of Tagetes patula. All the secretory structures in seedling and in flowering plants showed a schizogenous origin. In particular, in T. patula seedlings canals were examined in roots and hypocotyl while secretory cavities were found in cotyledons. In flowering T patula plants, canals in epicotyl and in flower corolla, as well as secretory cavities in leaves and flower bracts were examined. Plastids related to the synthesis and accumulation of lipid substances involved in the secretory process were then identified in some glandular structures. X-ray microanalysis showed the presence of sulfur in the secretory tissue cells and, above all, in the secretion itself. This supports the hypothesis of direct involvement of the T patula glandular structures in the production of thiophene compounds.