PEG8000 use for water deficit

Hi colleagues,
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I want to use PEG8000 to introduce water deficit stress to Arabidopsis roots. What is the suitable concentration of it to induce mild dehydration stress, eg. in 1/2x MS medium? I do not like high concentration as it may causeplasmolysis (I personally do not like 200 or 300 mM NaCl used by so many Arabidopsis researchers in salt stress study). However, a too low concentration of PEG8000 may have slow effect in a short time. Is there anyone knowing a reasonable concentration of it in hydroponics system of Arabidopsis? I want to harvest the tissue in a few hours (less then half a day). How about10% or 15%?* Low concentration stimulates root elongation while high concentration won't, according to some references.
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Thanks for your input.