26. Brown, Jr. R. M. and H. J . Arnott.
1970. Structure and function of the algal pyrenoid. I. Ultrastructure
and cytochemistry during zoosporogenesis of Tetracystis excentrica.
J. Phycol. 6:14-22.
26. Summary
The fine structure of the pyrenoid in the
mature vegetative cell of Tetracystis excentrica Brown
and Bold is described. During zoosporogenesis, the pyrenoid undergoes
regression, and the ultrastructure of this process is described
in detail. The ground substance undergoes dissolution, and reticulate
fibrillar structures appear as well as intruding chloroplast thylakoids.
Pyrenoid-associated starch plates diminish, and quantities of
starch not associated with the pyrenoid are produced. New pyrenoids
appear late in the division cycle after all other major organelles
associated with the motile cell have been formed. Zoospore pyrenoids
develop in thylakoid-free spaces of the chloroplast which are
similar to the DNA-containing regions. The new pyrenoid ground
substance, which is loosely fibrillar, arises in close proximity
to starch grains which may be formed in the stroma. Then the
zoospore pyrenoid produces 2 hemispherical starch plates identical
to those in the mature vegetative cell. Zoospore pyrenoids lack
the 2 convoluted thylakoids between the starch plates and the
ground substance characteristic of those in the mature vegetative
cell. Instead, the thylakoids are identical to those of the chloroplast
at first, and then develop into a convoluted state in the vegetative
cell. Cytochemical tests for DNA, RNA, and protein were made
for the cytoplasm, nucleus, nucleolus, and pyrenoid. Conclusive
evidence is presented for the presence of RNA in the cytoplasm
and nucleolus, DNA in the nucleus, and protein in the pyrenoid.
The tests did not conclusively demonstrate the presence or absence
of DNA and RNA in the pyrenoid; however, they suggested that small
amounts of both DNA and RNA may be present.