Cytokinin production by Asparagus shoot apex cultured in vitro

The cytokinin producing capacity of asparagus (Asparagus officinalis L.) shoot apex was examined by means of shoot apex culture in vitro, where adventitious roots were never formed. The cultured shoot apices continued to diffuse a small but constant amount of cytokinin into the medium throughout five passages of subculture. The cytokinin content in the apices at the end of the subculture was not different from that at the beginning of the subculture. These results indicate a production of cytokinin by the apices. However, the finding is not in conflict with the hypothesis that the root tip is the major source of cytokinin supply, because the root tip of asparagus produced more cytokinin than the shoot apex and the decline of shoot growth observed during the subculture was partially restored by an application of zeatin into the medium.