Changes in enzyme activity during elongation and tuberization of stolons of <italic>Solanum tuberosum</italic> L. cultured in vitro

Isolated stolons of Solanum tuberosam L. were cultured in vitro in the presence of kinetin, which induced tuber initiation or gibberellic acid which inhibited initiation. Progressive changes in enzyme activity, at the locus of tuber initiation, were monitored at specified intervals. In the presence of kinetin soluble invertase activity was decreased with time whereas gibberellic acid (GA) evoked substantial increases in activity. Acid phosphatase activity was enhanced by GA but changed only slightly under tuber inducing conditions. Enzymic hydrolysis of glucose-6-phosphate and fructose-6-phosphate decreased during the course of tuber induction but increased in the presence of GA. In contrast hydrolysis of 3'AMP was stimulated under tuber inducing conditions. GA evoked substantial increases in peroxidase activity during the initial stages of incubation while under tuber inducing conditions increased activity was only observed after 5 days. Substantially higher levels of IAA oxidase activity were associated with tuber initiation. RNase activity decreased with time under tuber inducing conditions but showed an initial stimulation in the presence of GA. These results are discussed with reference to the role of these enzymes in carbohydrate metabolism and the regulation of hormone levels.