Mevalonate-derived quinonemethide triterpenoid from in vitro roots of Peritassa laevigata and their localization in root tissue by MALDI imaging

Abstract

Biosynthetic investigation of quinonemethide triterpenoid 22β-hydroxy-maytenin (2) from in vitro root cultures of Peritassa laevigata (Celastraceae) was conducted using (13)C-precursor. The mevalonate pathway in P. laevigata is responsible for the synthesis of the quinonemethide triterpenoid scaffold. Moreover, anatomical analysis of P. laevigata roots cultured in vitro and in situ showed the presence of 22β-hydroxy-maytenin (2) and maytenin (1) in the tissues from transverse or longitudinal sections with an intense orange color. MALDI-MS imaging confirmed the distribution of (2) and (1) in the more distal portions of the root cap, the outer cell layers, and near the vascular cylinder of P. laevigata in vitro roots suggesting a role in plant defense against infection by microorganisms as well as in the root exudation processes.

Figure 1. Quantification of maytenin (1) and 22β-hydroxy-maytenin (2) in P. laevigata adventitious roots cultured in vitro (dry weight).

The roots were cultured for 84 days under dark conditions in WPM medium supplemented with 2% glucose (w/v), PVP (899.74 μM), and IBA (19.68 μM).

Figure 2. Biosynthetic studies using 1-¹³C-D-glucose as precursor showed that the biosynthesis of quinonemethide triterpenoids 1 and 2 proceeds via mevalonate pathway.

Figure 3

Transverse sections of root tissues from Peritassa laevigata obtained from different parts (root cap, differentiating region, and primary structure) and their MALDI-MS images reconstructed with ions m/z 443.2562 [M + Na]⁺ (A,C) and 459.2511 [M + Na]⁺ (B,D) corresponding to maytenin (1) and 22β-hydroxy-maytenin (2), respectively. CP: cortical parenchyma; Ed: endoderm; Ep: epiderm; VC: vascular cylinder.