German drug and farm chemical company Bayer AG says it has signed a deal to acquire seed and weed-killer company Monsanto for $66 billion in cash.

Bayer says it is paying Monsanto shareholders $128 per share, which represents a 44 percent premium over Monsanto's closing price on May 9, the day before a proposed deal was announced.

The deal is subject to approval by Monsanto shareholders and anti-trust regulators.

Bayer said Wednesday the transaction brings together two different but complementary companies. Bayer makes a wide range of crop protection chemicals, while Monsanto is known for its seeds business.

Leverkusen-based Bayer said the merged companies' agriculture business would have its seeds business and North American business headquarters in St. Louis, Missouri, where Monsanto is currently based.