I am confused regarding this PGR concentration.Till date I have done all my experiments using mg/l method. Many like me has also done the same. But recently I have encountered certain issues where the scientists are advocating micromolar approach is more acceptable over mg/l. Which one is acceptable?
As per my knowledge, mg/l is more acceptable. Even micromolar approach can also be adopted, if those species is responds to micromolar approach. mg/l is more acceptable.
Its all depends on the crop species you are working, hardy species may require more concentration of PGR compare to soft crop species.
I used to use mg/L for my experiments but it seems better to report the PGR concentrations used in the experiments as micromoles. If you want to compare the effect of specific PGR combinations in your tissue culture, then you compare the concentrations of them in micromoles. Let’s say you want to study the effect of two auxins for callus induction, then you have to add to your media same micromoles of the two auxins, meaning same number of molecules of the two auxins that can interact with the plant tissue, therefore the mg/L of one auxin will be different to the other one. If in this hypothetical case we are comparing IAA and 2,4-D then in a medium you would need to add 0.175mg/L of IAA to get 1uM, and to the other medium you would need to add 0.22mg/L of 2,4-D to get 1uM.
I hope this explanation is clear and useful.
Indeed, I agree that micromolar is more correct, because the effect of all substance is according to number of molecules that cell has accesss. So, when we use the same weight (mg/L) of two PGR different molecular weight, we are taking different molecules quantities of each PGR. Consequently, the final results comparison will be inaccurate. The same goes for the other components of the medium as carbon comparasion of carbon sources (sugars). Take a look at the article Paiva Neto et al (2003). Carbon sources and their osmotic potential in plant tissue culture: does it matter? Scientia Horticulturae 97 (2003) 193–202
I agree that the PGR concentrations expressed in micromolar quantities are a better practice because after all the number of molecules (and not their weight per se) would be responsible for their effect. This would be especially true if you need to compare the activities of different PGRs.
Molar concentrations are more appropriate than weight basis because PGRs are handled/ active in very low quantity, it is the number of molecules per unit volume available for interaction in important to cause the effect.
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