The described experimental set-up with L. gibba as test organism appears to be a promising new model system to investigate effects of potentized substances. Yet larger sets of replication experiments with selected test substances and systematic negative controls are necessary to verify the effects found.
BackgroundIn ecotoxicological and environmental studies Lemna spp. are used as test organisms due to their small size, rapid predominantly vegetative reproduction, easy handling and high sensitivity to various chemicals. However, there is not much information available concerning spatial and temporal stability of experimental set-ups used for Lemna bioassays, though this is essential for interpretation and reliability of results. We therefore investigated stability and natural variability of a Lemna gibba bioassay assessing area-related and frond number-related growth rates under controlled laboratory conditions over about one year.Methology/Principal Findings
Lemna gibba L. was grown in beakers with Steinberg medium for one week. Area-related and frond number-related growth rates (r(area) and r(num)) were determined with a non-destructive image processing system.To assess inter-experimental stability, 35 independent experiments were performed with 10 beakers each in the course of one year. We observed changes in growth rates by a factor of two over time. These did not correlate well with temperature or relative humidity in the growth chamber.In order to assess intra-experimental stability, we analysed six systematic negative control experiments (nontoxicant tests) with 96 replicate beakers each. Evaluation showed that the chosen experimental set-up was stable and did not produce false positive results. The coefficient of variation was lower for r(area) (2.99%) than for r(num) (4.27%).Conclusions/SignificanceIt is hypothesised that the variations in growth rates over time under controlled conditions are partly due to endogenic periodicities in Lemna gibba. The relevance of these variations for toxicity investigations should be investigated more closely. Area-related growth rate seems to be more precise as non-destructive calculation parameter than number-related growth rate. Furthermore, we propose two new validity criteria for Lemna gibba bioassays: variability of average specific and section-by-section segmented growth rate, complementary to average specific growth rate as the only validity criterion existing in guidelines for duckweed bioassays.
Homeopathic potencies are used as specific remedies
in complementary medicine. Since the mode of action is
unknown, the presumed specificity is discussed controversially.
Objective: This study investigated the effects of potentised substances
on two yeast species, Saccharomyces cerevisiae and
Schizosaccharomyces pombe, in a stable and reliable test system
with systematic negative controls. Materials and Methods:
Yeast cells were cultivated in either potentised substances or
water controls in microplates and their growth kinetics were
measured photometrically. Water control runs were performed
repeatedly to investigate the stability of the experimental set-up
(systematic negative controls). Results: 4 out of 14 screened
substances seem to have affected the growth curve parameters
slope or yield. Out of these substances, azoxystrobin and phosphorus
were chosen for 8 further replication experiments,
which partly confirmed the results of the screening. On the average
of all experiments, azoxystrobin affected the slope of the
growth curve of Saccharomyces cerevisiae (p < 0.05), and phosphorus
affected the slope of the growth curve of Schizosaccharomyces
pombe (p < 0.05). No effects were seen in the water
control runs. In addition, significant interactions between treatment
with potentised substances and experiment number were
observed in all experiments with potentised substances (p <
0.01), but not in the water control runs. Conclusions: Both yeast
species reacted to certain potentised substances by changing
their growth kinetics. However, the interactions found point to
additional factors of still unknown nature, that modulate the effects
of potentised substances. This stable test system with
yeasts may be suitable for further studies regarding the efficacy
of homeopathic potencies.
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