the inhibitory properties of and mode of action of plant essential oils ...

Characteristic of most eukaryotes is the ability to degrade and recycle proteins from
within the cell or those which are either endocytosed or phagocytosed. Higher
eukaryotes have early endosomes responsible for the internalisation of proteins and
their subsequent return to the cell membrane or transport to late endosomes. This is
followed by their transport to and degradation by lysosomes. Although Giardia is a
eukaryote, it appears not to have this early / late division of endosomes. This was
demonstrated in experiments by Lanfredi-Rangel et al. (1998) which showed that
when incubated with horseradish peroxidase, the PVs of Giardia were labelled
rapidly after a few min and that this labelling persisted even after several h.
In the same experiments by Lanfredi-Rangel et al. (1998) also suggested a lysosomal
function to the PVs because of the localisation of acid phosphatase within most of
the vesicles and also in the cisternae of the ER. Glucose-6-phosphatase localisation
(a marker of ER) showed the formation of an electron-dense reaction product within
the ER but also within a few of the PVs. This suggested that the PVs show continuity
with the ER. Earlier experiments (Lindmark 1988; Feely & Dyer 1987) demonstrated
the PVs’ lysosomal functions through various hydrolase, proteinase and RNAse
activities. These experiments suggest that the early/late endosomal and lysosomal
system, which act discretely in higher eukaryotes, can be found as a single unit in
Giardia’s peripheral vesicular network and act in concert with the ER.
Although structures consistent with the ER had been described in Giardia by EM, it
wasn’t until experiments by Gupta et al. (1994) showed the presence of the BiP gene,
a hsp70 (heat shock protein) homologue found in the lumen of the ER in higher
eukaryotes, which is responsible for the folding and translocation of proteins across
the ER membrane, using molecular techniques and later Soltys, Falah and Gupta
(1996) demonstrated that BiP antibodies localised to ER-like structures that the
presence of an ER was confirmed.
The presence of three protein-disulphide isomerase genes (gPDI-1, 2 and 3) and their
expression provided further evidence of an ER within Giardia as these enzymes are
known to be within the lumen of the ER (Knodler et al. 1999). A major function of
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