Formation of Phenolic Substances in the Ray Parenchyma of Angiosperms

Abstract

IN the course of an investigation into the origin of phenolic substances in ray parenchyma (Wardrop and Cronshaw, in preparation), it has been observed that some of these substances appeared to originate in structure limited by a double membrane, the form and dimensions of which are similar to those of amyloplasts, frequently observed in this tissue (Cronshaw and Wardrop, in preparation). Fig. 1 shows a transverse section of a ray cell from Eucalyptus elaeophora after fixation with potassium permanganate. The pattern of distribution of phenolic substances was observed to be the same after fixation with the ferrous sulphate-formaldehyde fixative for tannins described by Johansen¹ although the cytoplasmic organelles were destroyed. In relatively mature material most of the cells had an appearance similar to that in Fig. 1 in which the iron staining or phenolic material showed poor fixation and penetration of the embedding medium. In younger material from the region adjacent to the cambium it was observed that phenolic substances were present in vesicles enclosed within an organelle which resembled a chloroplast, the regular structure of which had been disrupted. In Fig. 2 three of these vesicles can be seen associated with lamellæ resembling the grana of normal chloroplasts. Further observations showed that these vesicles arose by the dissolution of starch grains within the modified chloroplast or the amyloplast, and that as the dissolution took place the phenolic substances were deposited around the periphery of the vesicle so formed (Fig. 3), until the whole vesicle became filled with the phenolic material (Fig. 4). At an advanced stage of differentiation the amyloplasts, or the modified chloroplasts, could be seen to be undergoing disintegration and the released phenolic substances were aggregated in great concentration at the periphery of the vacuole (Figs. 4 and 5). In cells in which the vacuole was large, the organelles were confined to the narrow border of cytoplasm (Figs. 5 and 6).