Normally you do not have to, osmolarity is adjust to obtain the best visual health of your cells. For protoplasts it's quite easy, they have to be round and not explosed
Yes, I agree with Dr. Eric answer. Also, make sure that the shaking speed is just adequate enough to provide momentum to the cells in enzyme solution. Otherwise, the protoplasts may look elliptical due to higher shaking speed. Off course, there are osmometers of several brands are available for this purpose for measuring the osmotic strength of enzyme solutions.
We adjust the osmolality with a clinical osmometer. This is a small instrument where you place few microliters of your solution and gives you a reading on the osmolality. You may need further conversions depending on the units. I may have a description in my papers of 2000 on water relations. Here I attach a link of a company http://www.aicompanies.com/index.cfm/products/?productId=7, this is not the model I used, but you can google for more. Ideally you should try to find a lab who can let you use one. It is not easy to calibrate them, they require extra careful manipulation of the samples to avoid contaminating the sensor... Cinta
Thank you all. I do not have any instrument for osmolality measurement. I am going to test the solution by making several mannitol concentrations to find the best condition.
Just use gradient levels of sugars (mannitol seems the best for your case) in several media, and count the healthy (ie round, later dividing) protoplasts under each medium. You may prefer to perform an FDA test too, but that will be necessary only once for your whole research; and if you follow the protocols, it wouldn't be crucial anyway.
It will be a good idea if you use the current mannitol level as control, and try 2 or 3 steps higher and lower the control level, on a linear basis.
I'm also agree with Eric Hosy. You could find many protocols that use mannitol at around 0.5M. I normally use this concentration with Abrabidopsis leaf protoplast, or 0.4M with tabacum. If you need the protoplast to do an experiment like those in the paper you have mentioned (i.e ionic transport), obviously you need to adjust the osmotic pressure taking into account all the compounds present in the solution, otherwise you could aproximate the osmotic pressure calculating it considering only the main compound: mannitol or sorbitol. Good luck!
Osmometer may be the more accurate way for adjusting the osmolallity
Normally we can adjust the osmolarity by adding mannitol, sucrose or sorbitol.
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