I have recently performed an experiment in which I tested the affects of phytotoxic cations on the rate of germination of the common navy bean. I did this out of curiosity, as I have recently been researching arsenic (III) and arsenic (V) mobility in water systems, and I wanted to know weather or not it was the mobility of the ion or its general toxicity to a cell that is more influential on the overall phytotocicity. Generally, arsenic (III) is much more toxic due to the fact that it is so mobile while arsenic (V) is less toxic due to the fact that it is less mobile. After testing the oxygen usage in each of my different germination environments, I was quite surprised at the results. I had placed 100 navy beans in 1 molar solutions of copper, lead, iron, and cobalt chloride (the lead chloride may have been a little under 1 M, as it is not very soluble in water); in each of these solutions, I let these beans germinate for 12 hours and then tested the oxygen output of each sample. Here were my results:

Divergence of Oxygen Concentration Over Germination Period Graph

I did not think the mobility of these ions would have such an effect, as I know lead is less mobile than other cations in water systems; however, my major problem is interpreting the top three results, all of which gave fairly similar results. I am having trouble figuring out where this result is coming from. I know that all of the ions are phytotocic to some degree, and I would expect all of the ions to have a detrimental affect on the germination of the seeds. Is it more likely that these findings are the result of the phytotocicity of the ions or the mobility of the cations across the cellular membrane?

  • $\begingroup$ This is a very interesting question and has a strong physical chemistry component, but I have some trouble understanding the data. Is germination expected to exhaust a finite oxygen supply in a growth chamber, and this is what the "divergence" indicates? Basically the metals are expected to inhibit cellular respiration? Why does lead and DI show similar results? $\endgroup$ – Night Writer Nov 22 '18 at 14:35
  • $\begingroup$ Also, you are monitoring cumulative oxygen consumption post-germination over ~2.5 h? For all measurements you measure difference with respect to initial measurement at time 0 and call this divergence? What data do you have otherwise on the health of the germinated beans? The large difference suggests to me that the germination of beans in lead and DI has proceeded faster but is arrested in the presence of the other metals, as indicated by their low oxygen consumption... $\endgroup$ – Night Writer Nov 22 '18 at 14:43
  • $\begingroup$ At the start of my experminent, I placed the beans that had already germinated in their respective toxic metal cation solutions for 18 hours into 5 separate containers (including my control, DI water); I then put 5 oxygen sensors into my germination chambers and measured the current oxygen levels inside of the containers. For 2.5 hours I measured the current oxygen levels of each of the different containers. The divergence of oxygen concentration is simply referring the the the difference between... $\endgroup$ – ELI JONES Nov 22 '18 at 16:16
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    $\begingroup$ My educated guess is that since the concentration of the heavy metals is so high (1 M seems very high), diffusion (distribution through diffusion of solvated ions) effects would be negligible. Discrimination through active uptake followed by specific cellular toxicity is probably most important in determining the effect. But that's a guess. You need to check refs for comparative cytotoxicity, there are plenty I am sure. You should also run repeat experiments to see variation across probes, chambers etc. $\endgroup$ – Night Writer Nov 23 '18 at 10:20
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    $\begingroup$ The metal toxicity question is inarguably more the domain of chemical biology, more than pure p-chem. $\endgroup$ – Night Writer Nov 23 '18 at 10:23

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