W. Gordon Whaley

The Golgi apparatus and an early stage in cell plate formation.

Glutaraldehyde-fixed, osmium postfixed root apex cells in successive stages of cytokinesis show the involvement of small vesicular bodies in cell plate formation. These bodies apparently are produced by the Golgi apparatus; beginning by metaphase, they invade the spindle, cluster in the equatorial regions of the cell, and seem to set up some condition essential for the fusion of large Golgi vesicles in the same region. The plate is formed by this fusion, during which the small vesicles are incorporated into it. Plate formation proceeds centrifugally, with spindle fibers and clusters of the small vesicular bodies marking the edges, around which vesicle-producing Golgi apparatus are grouped. Puromycin affects either the production of the small vesicular bodies or their movement away from the Golgi cisternae. Colchicine precludes fusion of the larger Golgi vesicles, apparently by preventing clustering of the small ones, perhaps indirectly through effects on the spindle.

Staining of cells of Zea mays root apices with the osmium-zinc iodide and osmium impregnation techniques.

In the three cell types designated as secreting, the OZI procedure stained only 1 to 3 cisternae at the proximal face of the Golgi apparatus, Neither secretory vesicles nor secreted materials showed staining. In other cells the Golgi apparatus was most commonly stained at both faces with unstained cisternae “sandwiched” between the stained ones. This latter pattern was also seen in dividing cells even though in these cells the apparatus produces materials to be “secreted” into the cell plate. Certain specialized internal membranes of the amyloplasts were also stained, as were, variably, the nuclear envelope, the endoplasmic reticulum, and some vacuoles. With osmium no staining of the Golgi apparatus was observed, the same internal plastid membranes were stained, and the nuclear envelope and endoplasmic reticulum showed variable staining. Neither procedure stained lipid droplets. The significance of these staining reactions for Golgi apparatus is discussed.

Intercisternal Elements of the Golgi Apparatus

In both vegetative and reproductive cells of various Nitella species, and in cells of other plant genera, there are fine, parallel, elongated elements lying between the cisternae of the Golgi apparatus but not in contact with the cisternal membranes.

Assembly, Continuity, and Exchanges in Certain Cytoplasmic Membrane Systems

Basic to the definition of a cell is a membrane separating the activities within it from the surrounding environment. In even the simplest organisms, the plasma membrane, or plasmalemma, bounding the cellular mass is characterized by definable structure and distinctive physiological properties. The structure, composition, and properties of membranes have all been subjects of extensive, interrelated studies. This work will de al with questions about their assembly, continuity, and exchange. Only brief consideration will be given to structure, composition, and properties to provide a basic understanding that will lend coherence to the other questions.

Membrane assembly and secretion in higher plants

In higher plants evidence concerning the pathway of membrane assembly and transfer during secretion is scant. In maize roots the polysaccharides of the secretory materials can readily be followed from the Golgi apparatus to the plasma membrane by using tritiated sugars and radioautography. How protein constituents of either the membranes or secretory products are moved to the Golgi apparatus, presumably from the endoplasmic reticulum, during the earlier steps in the process is unclear. Radioautography after amino acid incorporation does not show high levels of labeling correlated with secretion nor is the intracellular pattern consistent with transfer of materials to the Golgi stacks. Whorls of endoplasmic reticulum membrane produced in the presence of ethanol can be preferentially labeled, but it remains uncertain whether proteins are transferred from the ER to other organelles. The precise interrelationship between the endoplasmic reticulum and the Golgi apparatus remains to be unequivocally demonstrated in most higher plant cells.

Development changes in the distribution of carbohydrates in the maize root apex

Abstract Qualitative and quantitative analyses of glucose, fructose, sucrose and starch were made on the first ten serial 1 mm segments of 3-, 4- and 5-day-old primary roots of Zea mays . On both a per segment basis and a per microgram dry weight basis glucose and fructose increase up to the fifth or sixth segment. Increased concentration of glucose and fructose are concomitant with cell elongation. They accompany not only the period of marked cell elongation, but also the cell enlargement that proceeds in that part of the root in which cell division is the dominant activity. In this region the increase of glucose and fructose is, however, at a much lower rate than in the so-called elongation region. In the second segment the concentration per dry weight of sucrose is at its peak and it exceeds that of glucose or fructose. Basipetal to the second segment, in the region of cell elongation, glucose and fructose are present in increasingly larger quantities than sucrose. On a quantity per segment basis starch is at its peak in the second segment, but the data expressed as concentration on a dry weight basis show, and electron micrographs confirm (unpublished data from this laboratory), that starch is more prevalent in the root cap and in certain cells basipetal to the apical region than in the cells of the division zone of the root.

The Golgi Apparatus in Plant Cells

During the early investigations there was little exploration of the possibility of the presence of the Golgi apparatus in plant cells. Several factors contributed to this situation. The early presumed analogy between the Golgi apparatus and the canals of Holmgren (1902) led to an assumption of equivalence between the Golgi apparatus and elements of the vacuome. This idea was supported in one form or another by Bensley (1910), Guilliermond and Mangenot (1922), and Guilliermond (1929). The association of the apparatus with secretion tended to de-emphasize plant cells, only a few types of which were recognized as secreting cells. Nonetheless, Bowen (1926) concerned himself with the question of whether plant cells contained Golgi apparatus. He developed an idea that the plastids might equate to the Golgi apparatus. This idea was picked up by Weier (1932) who gave credit for it to Bowen. Bowen subsequently undertook a detailed study of plant cells and concluded that he could demonstrate the normal components of animal cells and something in addition, to which he applied the term osmiophilic platelets which were much more demonstrable in certain tissues than in others (Bowen 1928). Having done so, he accepted the equivalence of these osmiophilic platelets and the Golgi apparatus.

Modifications and Dysfunctions

Modifications of the Golgi apparatus are difficult to deal with because of the many, varied forms of the organelle, its extensive changes with activities of the cell, and significant alterations during the period of development and differentiation.

The Formation of Structural Components

Cells responsible for chondrogenesis were among the favorite objects for study in the early phases of the investigation of the Golgi apparatus. Then when attention turned to secreting glandular cells, chondrocytes were somewhat neglected.