I don't think there is a standard cell line(s) to check toxicity of any compound because each cell line obtained from different part of the body. usually choosing the cell line depends on the aim of the study.
Every plant extract have different properties for different tretments so we can never use same cell line always for the study. We have to design the study according to our plants medicinal properties.
there are no such standardization for cytotoxicity assay by any diffrent assay like MTT,MMT or XXT nd it depends on ur aim of experiment nd its objective like if working with breast cancer thn use std. Hela or SiHa nd ny one could help u more if u make clear wid ur wrking objective or for general checking use fibroblast or CHO line....best of luk
It really depends on your objective, the kind of toxic compound you want to assay. I have tested toxicity of ribossome-inactivating proteins (ricin and curcin) using Vero cells, wich is a standard cell line used to those proteins.