DEVELOPMENTAL SEM OBSERVATIONS ON AN EXTRACELLULAR-MATRIX IN EMBRYOGENIC CALLI OF DROSERA-ROTUNDIFOLIA AND ZEA-MAYS

Primary embryogenic callus of Drosera rotundifolia and long-term cultu red embryogenic callus of Zea mays possess a conspicuous extracellular matrix (ECM) around and between embryogenic cells. The structural arr angement of ECM depends on the developmental stage of the embryogenic cells. Single embryoid cells were covered with, and connected by net-l ike material. However, surface cells of young globular embryoids were covered with a coherent layer of ECM which forms bridges with net-like material between the cells which was gradually reduced to coarse stra nds. When protodermis was formed on the surface of globular embryoids, the ECM disappeared completely. The ECM network was never observed on the surface of heart- and torpedo-shaped embryoids. Safranine (especi ally 0.1%) stabilized the structure of ECM. Digestion with pronase E a nd proteinase K indicated that the ECM contains proteinaceous componen ts. Similar developmental patterns of ECM were observed in dicotyledon ous and monocotyledonous examples. The ECM represents a stable morphol ogical structure even during long-term embryogenic culture in maize.