Nicotine levels in non fruit/edible parts of plants (that are not tobacco)
Tomato leaves have something like 184 ng/g of nicotine, in the same ballpark as tomatoes (the fruit) and not close to tobacco.  I think this is not peer-reviewed, but it cites other papers that are: Nicotine Analysis in Several Non-Tobacco Plant Materials
And this is a PDF of a slide deck providing a simple presentation of the results from the same article: Nicotine Analysis in Several Non-Tobacco Plant Materials - PDF