>"But it has what we like to call one fatal flaw," Cavanagh continues. Unfortunately, Rubisco isn't picky enough about what it grabs from the air. It also picks up oxygen. "When it does that, it makes a toxic compound, so the plant has to detoxify it."

Can someone explain this, the article doesn't go into much detail. What is this toxic compound, and why must the plant make it?

edit: Explained in detail in this article: https://arstechnica.com/science/2019/01/re-engineering-photo...