ARCHITECTURE OF THE FLUID CELLULOSIC ARRAYS IN THE EPIDERMIS OF THE QUINCE SEED

Using thin-sectioning for electron microscopy, including the careful examination of a long series of sections which contained several complete cells, we describe the form of the contents of the unusually enlarged distal periplasmic space in the epidermis of the seeds of Cydonia oblonga. The major feature is a large stack of cellulosic material arranged helicoidally, which previous work has indicated is fluid and similar to a cholesteric liquid crystal. This stack has a serrated margin, which is interpreted as indicating a surface shaped like that of a screw or a concertina. The overall shape based upon artistic reconstructions from serial sect?? shows great ?? variability, due in part to the limits set by the enclosing cell walls. This together with observations of variation in helicoidal pitch and of helicoidal arc reversal, indicates that the crystals are highly plastic in form. It is suggested that the form is determined by a combination of intrinsic and extrinsic factors. Not all microfibrils in the periplasmic pocket are arranged helicoidally, and it is argued that the coexistence of helicoidal and non helicoidal microfibrillar arrays indicates that a gradient of an agent which controls cellulose microfibrillar architecture is present. This may indicate that cell wall architecture can similarly be determined by subtle regulation of agents which control helicoidal pitch. © 1990.