Secretory structures in stems of five lianas of Paullinieae (Sapindaceae): Morphology and histochemistry

Paullinieae lianas are noteworthy for possessing cambial variants, so it is not surprising that the structure of the vascular system has been the focus of most of anatomical studies involving these plants. However, secretory structures remain understudied in the tribe and in the family Sapindaceae as whole. This study aims to characterize the secretory structures in the stems of five lianas of Paullinieae in order to better understand their morphology and histochemistry. Stem anatomy was analysed using light microscopy and the chemical composition of their secretory structures was determined histochemically. Three secretory structures were found: idioblasts, glandular trichomes and laticifers. Tannin-containing cells (idioblasts) are distributed throughout the stems. Glandular trichomes are capitate and have a complex mixture of phenolic compounds, tannins, proteins and polysaccharides. Laticifers occur in primary tissues, and are also observed in the secondary structure of Serjania pernambucensis Radlk.; they occur in regular and variant phloem (cambial variant), arranged in clusters due to divisions of pre-existing laticiferous cells. This phenomenon has not been reported previously. Additionally, this is the first detailed study of laticifers in primary and secondary structure of stems of lianas of Sapindaceae. The laticifers are articulated and non-anastomosing, containing the following chemical components: rubber, lipids, proteins, polysaccharides and terpenoids. Future studies might provide a broader understanding of the morphological diversity and the role of secretory structures in the tribe.