The Development of Fibre-Tracueid Pit Membranes in Pyrus Communis L.

Abstract

The development of fibre-tracheid pit membranes in Pyrus communis L. has been studied using transmission electron microscopy. Pit fields in the radial walls of cambial cells in transverse section contain isolated plasmodesmata. As cell enlargement proceeds, groups of plasmodesmata develop within thickenings of the future pit membrane. These thickenings are covered by amorphous, secondary-wall-like material (the torus-like structures found in mature pits by Parameswaran ' Liese, 1981) just prior to the end of differentiation and cytoplasmic autolysis. It is suggested that this cap of material acts as aseal, preventing passage of autolytic enzymes from a dying cell to its living neighbour via the perforations occupied by plasmodesmata.