Leaf development and anatomy of in vitro-grown Polygala paniculata L. are affected by light quality, gelling agents, and sucrose

Abstract

Plant in vitro growth performance is influenced by environmental, physical, and chemical conditions. The present study evaluated the mutual effect of light, gelling agents, and sucrose concentration on leaf anatomical structure of in vitro-grown Polygala paniculata. Nodal segments were inoculated on agar- or Phytagel®-gelified medium supplemented with 15 g L−1 or 30 g L−1 sucrose. Cultures were grown under fluorescent lamps, light-emitting diodes (LEDs) with white light, and LEDs with blue and red light at 56 µmol m−2 s−1 photon flux. After 45 days of culture, leaf histology was assessed. The leaves of P. paniculata had an uniseriate epidermis and dorsiventral mesophyll. Gelling agents had antagonistic effects in relation to sucrose concentration. Growth on agar and 30 g L−1 sucrose induced greater leaf blade thickness, with expanded palisade and spongy parenchyma but looser intercellular spaces. In contrast, growth on Phytagel® led to significantly thicker palisade parenchyma at 15 g L−1 sucrose. Fluorescent lamp light favored in vitro leaf development of P. paniculata grown on agar; whereas spectral quality had no effect on leaf blade thickness in Phytagel®-grown plants. In summary, mutual combinations of gelling agent, light quality, and sucrose concentration influence the establishment and anatomic structure of leaves in P. paniculata plantlets grown in vitro. This result will facilitate studies on in vitro propagation of this important medicinal species.