Leaf Determination in the Fern Osmunda cinnamomea--A Reinvestigation

Earlier studies of leaf determination in the fern Osmunda cinnamomeaL., using the technique of excision and sterile culture, indicatedthat the apices of incompletely determined leaf primordia areconverted into shoot apices after isolation. Subsequently otherworkers questioned this interpretation, suggesting that a primordiumis determined as a leaf shortly after its inception and thatany shoot which arises from it is an adaxial adventitious bud.Because of the importance of this distinction in the interpretationof determination, the phenomenon has been reinvestigated byscanning electron microscopy and histological methods. Sincefixation for electron microscopy was inconsistence, the workwas performed on the primordia using resin models formed indental plastic moulds. Our data, on explanted P3, P4, and P5leaf primodia, provide strong confirmation for the interpretationthat the leaf apex is indeed converted to a shoot apex in incompletelydetermined primodia after explantation. This new evidence formsthe basis for interpreting leaf determination in this experimentalsystem.Copyright 1993, 1999 Academic Press Leaf determination, in vitro, surface replica, scanning electron microscopy, Osmunda cinnamomea L., cinnamon fern