Histochemical evaluation of induction of somatic embryogenesis in Passiflora edulis Sims (Passifloraceae)

Abstract

The aim of this study was to describe the accumulation of reserves during the somatic embryogenesis process in Passiflora edulis Sims FB-300, obtained from mature zygotic embryos, using histochemical methods. Mature zygotic embryos were inoculated in Murashige and Skoog induction media supplemented with 31.06 μM of picloram, 2.22 μM of benzyladenine, and 2.27 μM of thidiazuron. The zygotic embryo explants, at different developmental stages, were collected and fixed in Karnovsky solution and subsequently subjected to dehydration in an ethanol series and embedded in acrylic resin. Transverse and longitudinal sections (5-μm thick) were stained with toluidine blue for anatomical characterization, using Xylidine Ponceau for the detection of total protein, periodic acid-Schiff reagent for neutral polysaccharides, Sudan black B to detect lipids, and Lugol’s reagent for the starch detection. Histological sections revealed the formation of protuberances and globular stage somatic embryos in the cotyledonary region of the zygotic embryo. Histochemical tests revealed the presence of large quantities of protein bodies in zygotic embryos of P. edulis, which were gradually metabolized during somatic embryo development. Lipid bodies and starch grains were identified only after 20 d of culture, suggesting the use of these compounds as energy source for de novo synthesis. The present study describes the anatomical changes and the pattern of reserve accumulation during the somatic embryogenesis process in P. edulis.