Comparison of tuber and shoot formation from in vitro cultured potato explants

The development of axillary buds of potato (Solanum tuberosum L.) plants, cultured in vitro, was analyzed. Depending on the composition of the culture medium, the buds developed into either tubers (medium with 8% sucrose), shoots (1% sucrose), or stolons (8% sucrose and 0.5 mu M gibberellin). Endogenous sugar and starch levels, and key-enzymes involved in the conversion of sucrose to starch were determined at different stages of development. Moreover, the spatial distribution of sugar levels and enzyme activities were determined within the developing structures. Glucose and fructose decreased upon tuber formation, most noticeably in the swelling parts, where also starch accumulated. The activities of sucrose synthase, fructokinase and ADP-glucose pyrophosphorylase were highest under tuber-inducing conditions, the increase being confined to the tubers, and absent in the subtending stolons. It is concluded that changes in the measured parameters, observed under tuberizing conditions, are specifically related to the formation of the tuber, and are confined to the swelling part only.