Although the original paper only described the biochemical analysis they performed, it seems that cultivating the plants in the lab was planned for their future work, with the intent of figuring out the biosynthetic pathway by radiolabelling possible precursors.
Good point - as I said, I am not a scientist, so that's what I wanted to know and your answer helps me understand.
In my mind, it seems like declaring that a plant is growing gold, without testing the ground (or doing a lab test), and later finding out that its roots are picking up the gold from a seam near the surface.
At some point you have to stop. For examples: what was the geological reason for the gold seam? What is the transport mechanism from the roots to the rest of the plant? What is the evolutionary advantage to grow gold? What are the genetic differences between that plant and similar plants?
It's impossible to cover everything, so you have to get an idea of what's interesting enough to publish.
Then when you do submit it for publication, the reviewers will say "have you tried X?", where X is something which takes a lot more time and funding than you have, and you really just want to be done with the paper.
