58. Brown, Jr. R. M. and D. K. Romanovicz.
1976. Biogenesis and structure of Golgi-derived cellulosic scales
in Pleurochrysis . I. Role of the endomembrane system in
scale assembly and exocytosis. Applied Polymer Symp. 28:537-585.
John Wiley & Sons, Inc., New York.
The Golgi apparatus of a marine haptophycean
alga, Pleurochrysis scherfellii, has been studied with
respect to its role in the assembly and transport of cell wall
scales. In the vegetative cell the scale consists of three morphologically
recognizable subunits: a quadriradial network of microfibrils
rich in galactose and acidic sulphated polysaccharides, a spiral
network of cellulosic microfibrils associated with a peptide rich
in hydroxyproline, and amorphous coating substances rich in acidic
polysaccharides. Scale structure, size, and composition is dependent
upon specific phases of the life history. Unlike vegetative scales,
those from the zoospore phase lack the amorphous coating substances
and are about half the dimensions. The ratio of radial-to-spiral
subcomponents remains unchanged. In the nutritionally induced
coccolith phase, the scale rim is modified to consist of two concentric
microfibrils. The ratio of radial-to-spiral subcomponents is
dramatically altered. Scale subcomponents are synthesized and
assembled in association with the membranes of the endoplasmic
reticulum and Golgi apparatus. Incipient Golgi membranes originate
from budding regions of the endoplasmic reticulum. Precursor
pools for radial subcomponents are differentiated from the spiral
subcomponents by dense reaction products of silver methenamine
when preceded by periodate oxidation. These pools which are about
to be incorporated into the forming face of the Golgi membranes
first appear within specific topographic regions of the endoplasmic
reticulum synthesized in a folded configuration. Cytochemical
enzyme localization reveals aryl sulfatase and alkaline phosphatase
activity in the region of synthesis of the radial microfibrils.
The radial microfibrils undergo an elaborate unfolding as observed
by the presence of distinct "Z-stages." Following unfolding
of the radial microfibrils, the spiral cellulosic microfibrils
are presumably crystallized within a central feeding tubule on
the distal face of the cisterna. Alkaline phosphatase activity
is pronounced in the zone of centripetal amorphous polysaccharide
addition. In vegetative cells, this sequence immediately follows
the synthesis and deposition of cellulosic microfibrils. Scale
transport to the surface and ultimate exocytosis involve a subsurface
cisterna which has the capacity to guide and direct Golgi cisternal
membranes to the plasma membrane and to transfer "spent"
Golgi membranes to an autophagic vacuolar system. Acid phosphatase
activity was prominent in the subsurface cisterna as well as the
distal region of the Golgi apparatus. Colchicine prevents scale
exocytosis and promotes autophagic consumption of accumulating
scales and their cisternal membranes. Control of scale exocytosis
seems to be under specific control of plasma membrane "acceptor"
regions and Golgi cisternal coated vesicle "donor" regions.
Protoplast rotation and exocytosis is discussed in terms of the