A method for producing leafy biomass from undifferentiated plant cells, the method comprising providing undifferentiated plant cells, contacting them with an agent that promotes differentiation of the cells into leafy tissue and growing the cells in a temporary liquid immersion culture system. This method of the invention may be used to produce polypeptides, and natural medicinal products, and can be used to capture carbon dioxide. A method of producing a polypeptide in plant cells in vitro comprising: providing undifferentiated plant cells containing chloroplasts that carry a transgenic nucleic acid molecule encoding the polypeptide, wherein the plant cells display homoplastomy； and propagating the cells according to the above method to produce leafy biomass containing the polypeptide.
