Histolocalization of chemotaxonomic markers in Brazilian Vernonieae (Asteraceae)

Abstract

Vernonieae are well represented in South America by subtribe Lychnophorinae, with 104 Brazilian species, some of them rare and endangered. Lychnophorinae are well known for producing metabolites of high pharmaceutical and chemotaxonomic value. Despite the importance of secondary metabolites in Lychnophorinae, there is still little evidence regarding the secretory structures responsible for producing these compounds. Therefore, in this study we investigated 15 species representative of the main lineages of Lychnophorinae, with the following objectives: to identify where the chemotaxonomic markers of Lychnophorinae are secreted and stored and in which developmental stage of the organ these metabolites are found. Samples of stems and leaves were processed according to the usual techniques in plant anatomy. It was found that the main sites of secondary metabolite biosynthesis are glandular trichomes, epidermal cells and parenchyma tissues. Metabolites from glandular trichomes, especially sesquiterpene lactones (STL), are prevalent in the early developmental stages of organs. The metabolite compounds stored in parenchyma tissues are mainly terpenoids, flavonoids and other phenolic compounds; young and expanded leaves are equally rich in metabolites. Thus, the information obtained in this study is essential for conducting chemotaxonomic studies in this group, helping to promote selective collection and conservation of species.

Characterization and evolution of secondary metabolites in Brazilian Vernonieae (Asteraceae) assessed by LC-MS fingerprinting

“…Histochemical analyses performed by Lusa et al . () for STLs also revealed that glandular trichomes were the main sites of biosynthesis and accumulation of this class of compounds. Conversely, the occurrence of some STLs only in crude extracts can indicate their presence in other secretion sites, such as epidermal and parenchymal cells, as suggested by Lusa et al .…”

“…Phenolics and trans ‐cinnamic acid derivatives were identified in crude or rinse extracts or in both, indicating that phenolic compounds may be present in glandular trichomes and internally in leaves and stems of Lychnophorinae, which is also suggested by histochemical reactions performed by Lusa et al . (). Among the flavonoids, some compounds were detected only in the rinse extract and are probably secreted only in glandular trichomes.…”

“…Conversely, the occurrence of some STLs only in crude extracts can indicate their presence in other secretion sites, such as epidermal and parenchymal cells, as suggested by Lusa et al . (). Moreover, histochemical identification of terpenoids widely distributed in parenchymal cells (leaves and stems) recorded by Lusa et al .…”

“…In our study, other flavonoids were detected only in the crude extract or in both extracts, possibly reflecting the positive histochemical reactions to flavonoids observed by Lusa et al . () in epidermal cells, in chlorenchyma and ground parenchyma in leaves and in parenchymal cells in stems, mainly in cortical and phloem parenchyma. Recent studies have also indicated that phenolic compounds such as flavonoids (Silva et al ., ) and coumarins (Tattini et al ., ) can be found in leaf epidermis and chlorenchymal cells.…”

“…and Prestelia eriopus Sch.Bip. because they do not have glandular trichomes (Lusa, Da Costa & Appezzato‐da‐Glória, ). In addition, crude extracts were prepared for stems and leaves (both powdered) to detect compounds in the inner parts of these organs.…”