The present invention provides methods and compositions for the production of recombinant plasminogen, microplasminogen, and fragments thereof in a duckweed expression system. It is the novel finding of the present invention that a duckweed expression system may be used to produce high levels of plasminogen and microplasminogen. The duckweed-produced plasminogen and microplasminogen can be activated to produce a polypeptide having protease activity. Thus, the invention encompasses methods for the expression of plasminogen, microplasminogen, and fragments thereof in duckweed, duckweed plants that are transformed with expression cassettes for the expression of plasminogen, microplasminogen, and fragments thereof, and nucleic acids comprising nucleotide sequences encoding plasminogen, microplasminogen, and fragments thereof, where these nucleotide sequences are modified to enhance their expression in duckweed.