Transport through the Golgi Apparatus by Rapid Partitioning within a Two-Phase Membrane System

The fine structure of the holothurian haemocyte is similar to that of the nucleated erythrocytes of lower vertebrates. Points of similarity include nuclear and nucleolar features, the distribution of haemoglobin, mitochondria, lysosomes, Golgi apparatus, and centrioles, and the presence of a marginal band of microtubules. Features apparently unique to this haemocyte are a canalicular system and an isolation membrane system. An interpretation of the functional relationships of the organelles is presented. Stages in the development and degradation of the haemocyte are also demonstrated. The morphological similarity of the holothurian haemocyte to lower vertebrate erythrocytes is attributed to functional analogy and parallel cellular adaptations, but not to homology.

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The amounts and rates of export of polysaccharides found within the membrane system of maize root cells

Biochemical Journal ◽

10.1042/bj1420139 ◽

1974 ◽

Vol 142 (1) ◽

pp. 139-144 ◽

Cited By ~ 49

Author(s):

Dianna J. Bowles ◽

D. H. Northcote

Keyword(s):

Endoplasmic Reticulum ◽

Cell Wall ◽

Golgi Apparatus ◽

Cell Surface ◽

Rough Endoplasmic Reticulum ◽

Membrane System ◽

Maize Root ◽

Wall Material ◽

Cell Wall Material ◽

Root Cells

1. Maize seedling roots were incubated in vivo with d-[U-14C]glucose for 2, 5, 10, 15, 30 and 45min. The total incorporation of radioactivity into polysaccharide components in isolated fractions was investigated, and the pattern of incorporation into different polysaccharide components within the rough endoplasmic reticulum, Golgi apparatus and exported material was analysed. 2. The membrane compartments reached a saturation value of radioactivity in polysaccharide components by 30min incubation. Radioactivity in exported polysaccharide continued to increase after that time. The latter was formed and maintained by a steady-state turnover of polysaccharide synthesis and transport from the membrane system. 3. If the only access of the slime polysaccharide to the cell surface is via dictyosome-derived vesicles, the amount of slime components in the Golgi apparatus would have to be displaced every 0.3min in order to maintain the observed rates of increase in slime. This is in contrast with a displacement time of about 2.5min that is necessary for polysaccharide components in the Golgi apparatus to produce the observed increase in cell-wall material. The activity of the membrane system in the production of maize root slime is 8 times as great as that of the membrane system involved in cell-wall synthesis. 4. If the amount of polysaccharide material in the Golgi apparatus is maintained only by inflow of polymeric material from the rough endoplasmic reticulum the total amount of slime components in the rough endoplasmic reticulum would have to be displaced every 7min to maintain a constant amount in the Golgi apparatus. If the endoplasmic reticulum contributed directly to the cell surface in the synthesis of cell-wall material, displacement times necessary to maintain the observed rate of polymer production would be very slow.

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