Individual and serial sections were used to obtain detailed information regarding the morphology and distribution of the partially coated reticulum (PCR) and to determine its relationship with dictyosomes in endocytotically active soybean (Glycine max. (L.) Merr.) protoplasts. The results confirm and extend the description of the PCR provided by T.C. Pesacreta and W.J. Lucas (1985, Protoplasma 125, 173-184) from whole cells of selected angiosperms. The PCR of soybean protoplasts consists of a set of interconnected tubular membranes bearing a clathrin-like coat over part of their cytoplasmic surface. A dilation, sometimes containing small vesicles, is frequently seen in this organelle. The PCR often appears associated with dictyosomes but also occurs independent of other cell organelles. Only one example of a direct connection between the PCR and dictyosomes was observed.Following adsorptive endocytosis of cationized ferritin, the label appears in the PCR within 2 min and accumulates with time. It is never observed in the membrane dilations. Serial sectioning established that dictyosomes are labelled with cationized ferritin around the periphery of several cisternae, including those on both sides of the same dictyosome.

The vegetative shoot apex of Helianthus annuus contains a central zone in which the cell nuclei are relatively large and stain faintly in the Feulgen reaction. Excised apices in the vegetative state were supplied with thymidine-H3 through their sterile, liquid culture medium. Autoradiography after 24 or 48 hours of feeding revealed no significant incorporation of the labeled precursor into central zone nuclei, but extensive incorporation in peripheral regions of the apex. It is concluded that during vegetative growth deoxyribonucleic acid (DNA) synthesis and mitosis are arrested in the central zone or reduced to an extremely slow rate. Microspectrophotometry, however, indicates that the central zone nuclei are not held at the 2C level. With the onset of flowering, cytological zonation disappears in the apex and the incorporation of thymidine-H3 is uniformly heavy throughout the apical region.

Fractions enriched in coated vesicles were obtained from protoplasts derived from suspension cultured Glycine max (L.) Merr. cells. Initial enrichment was achieved by isopycnic centrifugation of a protoplast homogenate through a linear sucrose gradient in a vertical rotor. The coated-vesicle fractions from this gradient were pooled and centrifuged through a second linear sucrose gradient in a rate zonal fashion to remove the larger contaminating membrane vesicles. The most prominent polypeptide in the coated-vesicle fractions, plant "clathrin", had a relative molecular mass of approx. 190 kdalton as determined by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Other enriched polypeptides included bands at 105, 100, 96, 64, 50, 38 and 32 kdalton. This method was compared with a procedure utilizing sucrose step gradients for preparing coated vesicles from soybean protoplasts. The effectiveness of the isopycnic-rate zonal centrifugation procedure was also tested for the preparation of bovine-brain coated vesicles.

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1981. The ultrastructure of the central zone cells of the shoot apex of Helianthus annuus. Can. J . Bot. 59: 2009-20 15. An ultrastructural study of the vegetative shoot apex of Helianthus annuus L. cv. Peredovic has shown that in most respects the cytoplasmic components of the central zone cells were similar to those of the mitotically active peripheral zone cells. For example, the mitochondria, dictyosomes, endoplasmic reticulum, ribosomes, and microtubules were not different either in their structure or in distribution in the two types of cells. The only striking difference found was the presence of starch-containing plastids in the central zone, primarily in the two tunica layers in this region, and their absence from peripheral and immediately subjacent regions of the meristem. Starch-containing plastids were observed in the differentiating pith cells. Plasmodesmata were observed in the central zone and in walls between central and peripheral zone cells. SAWHNEY, V. K., P. J. RENNIE et T. A. STEEVES. 1981. The ultrastructure of the central zone cells of the shoot apex of Helianthus annuus. Can. J . Bot. 59: 2009-2015.Une Ctude ultrastructurale de l'apex de la pousse vCgCtative de 1'Helianthus annuus L. cv. Peredovic montre que les composantes cytoplasmiques des cellules de la zone centrale sont, sous presque tous les rapports, semblables a celles des cellules mitotiquement actives de la zone pCriphCrique. Par exemple, les mitochondries, les dictyosomes, le rCticulum endoplasmique, les ribosomes et les microtubules sont semblables chez les deux types de cellules, aussi bien dans leur structure que dans leur localisation. La seule diffkrence frappante consiste en la presence de plastes contenant de l'amidon dans la zone centrale, surtout dans les deux couches de la tunica dans cette rCgion, et en leur absence de la rkgion pCriphCrique et des rkgions irnmkdiatement sous-jacentes du mCristkme. Des plastes contenant de l'amidon ont Ct C observCs dans les cellules de la moelle en diffkrenciation. Des plasmodesmes ont Ct C observCs dans la zone centrale et dans les parois entre les cellules de la zone centrale et celles de la zone @riphCrique.[Traduit par le journal]