I think that depends on the plant extract concentration. Generally for antimicrobial test researchers are using 2% of DMSO. If it's unknown drug then you have to try it from lower % up to 2% to see its solubility. Hope it will help you. Best of luck
I dont think that you can use upto 2% because 2% DMSO is able to kill the cells as well. In my opinion, if you use DMSO to dissolve your plant extracts then the final concentration of it should be maximum 0.1% or lower than that. I also use DMSO for some of my cell based work and never used more than 0.1% in its final concentration.
I have some experience using DMSO for the carrier to test the antimicrobial activity from all plant essential oils. I have no problem to use it, but will use DMSO as a control as well. For my experiments, I did not dissolve to any diluted concentrations, just use it like a solvent. It worked fine. Just for your reference.