SEM Characterization of an Extracellular Matrix Around Somatic Proembryos in Roots of Cichorium

Roots of in vitro plantlets of a hybrid Cichorium intybus L. × C. endivia L. placed for 10 d in an agitated liquid induction medium in darkness at 35 °C give somatic embryos of various sizes which disrupt the epidermis. Proembryos can be observed inside the root; they show a fibrillar network linking the surface cells. The network is observed in agitated and static liquid medium; it is not well developed on solid medium. It is not removed by lipid solvents and pectinase but disappears partly with protease. Ether-methanol (1:1 v/v) for 45 min and Tris-HC1 buffer for 3 h at 30 °C destroy it. As in animal cells such external proteic networks are constituents of an extracellular matrix linked to the cytoskeleton, we tested microtubule destabilization by colchicine and cold treatments which removed the network; this effect was reversed by DMSO and high temperature.