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Like other cells Paramecium has peroxisomes. These organelles
are usually smaller than mitochondria and have a granular appearance
and contain a few tubular-like inclusions. These tubules have not been
conclusively shown to be continuous with the single limiting membrane
of this organelle. In this case the peroxisome has a microtubule lying
along its surface. This cell was exposed to HRP for 30 seconds and
then chased in HRP-free medium for 3 minutes. The subsequent
incubating with hydrogen peroxidase and diaminobenzidine resulted in
an electron opaque reaction product in the peroxisomes not because
they took in HRP but because the peroxisomes contain large amounts of
catalase that results in the reduction of hydrogen peroxidase. HRP can
only enter the living cell by endocytosis, phagocytosis, when
trichocysts are discharged, at the open cytoproct or when a CV opens.
EM taken on 6/13/79 by R. Allen with Hitachi HU11A TEM. Neg. 22,500X.
Bar = 0.25µm.
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