Nicotine levels in non fruit/edible parts of plants (that are not tobacco)

I am an ex smoker who now vapes (uses e-cigs). Various authorities are equating vaping with smoking by calling it a ‘tobacco product’ – which is in a sense true given that the majority of nicotine sold is extracted from the leaves of tobacco. I am interested in the practicality (or otherwise) of extracting nicotine from other botanical sources.

Of course, it is not just tobacco that contains nicotine, it is common in other plants of the nightshade family, as suggested by The Nicotine Content of Common Vegetables & Nicotine: Occurrence and biosynthesis. The second source notes:

Nicotine is a natural product of tobacco, occurring in the leaves in a range of 0.5 to 7.5% depending on variety.[84] Nicotine also naturally occurs in smaller amounts in plants from the family Solanaceae (such as potatoes, tomatoes, and eggplant).[85]

Reference 85 points back to the first link, which shows this table.

But looking at the numbers, it seems unlikely. At even .5%, the ‘low nicotine’ tobacco leaf comes in at 5 mg/g, which is 5,000,000 ng/g – around 50,000 times more concentrated than eggplant. In fact, here is a graph of the log₁₀ value (2 is ten times larger than 1) of each.

On the other hand, the ability of a plant to produce nicotine is retained and handed down to ancestors because nicotine is a pesticide that ..discourages insects from eating the plant, and larger herbivores will also get sick if they eat too much of it. Logically, levels of nicotine would be higher in the leaves and stems of a plant than in the fruits/food that we & animals are more interested in eating. That again makes sense, since most fruits are ‘designed’ to be put through the stomach of a larger animal as part of the process of regeneration.

That logic seems to be borne out by the levels of nicotine in tomatoes, that start around 40 ng/g in green tomatoes, but end up at just over 4 ng/g in ripe tomatoes (not sure what’s going on with that ‘pureed tomato’ level of over 50 ng!). The drop suggests to me that’s the plant’s way of preventing consumption while the fruits are still developing, but making them safe(r) to eat once ripe.

But what about the nicotine content in the leaves of those plants? Logically they might have a higher nicotine content. Does anyone know of studies of the levels of nicotine in the other parts of plants of the nightshade family?