Anatomical and histological features of Ilex paraguariensis leaves under different in vitro shoot culture systems

Abstract

Ilex paraguariensis (Aquifoliaceae) is an evergreen tree traditionally used to prepare a caffeine-rich infusion that has several medicinal properties. The in vitro propagation of this species has been studied as an alternative to conventional methods such as cuttings and seedlings. The in vitro culture environment consists of closed flasks with high relative humidity, reduced gas exchange and low luminosity conditions, which may induce physiological, anatomical and histological disruption in the cultivated plants. The occurrence of anatomical and histological alterations to the leaves of I. paraguariensis was examined in plants cultivated under greenhouse and different in vitro conditions. The variations in the microclimate inside the culture vessels generated by the different treatments tested affected the anatomy and histology of I. paraguariensis leaves by causing alterations in their architecture, thickness, vascularization and stomatal differentiation. A temporary immersion system was the best treatment for conserving the anatomical and histological characteristics of the leaves. This treatment led to the lowest stomatal index and an extensive system of intercellular spaces that were similar to the characteristics developed under external environment conditions.