Kinetin-induced tuberization of potato in vitro: on the mode of action of kinetin.

The tuberization percentage of etiolated potato (Solatium luberosumL.) sprout sections cultured in vitro in the absence of kinetinwas 61% (endogenous tuberization potential). The presence of5 mg/liter kinetin in the medium increased tuberization to 94%. In a time course experiment soluble ADP glucose: -l,4-glucan-4-glucosyl transferase (starch synthetase) activity extractedfrom etiolated sprout sections cultured in vitro remained low(one twenty-fifth of the activity present in the mother tubersat time 0), and was almost constant throughout 21 days of culture.No difference in activity was found in sections grown in kinetin-containingmedium in comparison with those grown in the absence of kinetin. During tuber initiation of etiolated potato stolons culturedin vitro, kinetin caused stimulation of phosphorylase activitywhich continued until the late stages of tuberization when italso stimulated ADP glucose pyrophosphorylase activity. Kinetindid not affect amylase activity. Addition of 11 mg/liter kinetinto the enzyme reaction mixture did not change the activity ofsolublestarch synthetase in vitro. The net accumulation of starch caused by kinetin was partiallythe result of the stimulation of starch biosynthesis throughphosphorylase at an early stage, and both phosphorylase andpyrophosphorylase at a later stage. ¹ Present address: Department of Horticulture, Washington StateUniversity, Pullman, WA 99163, USA. (Received January 6, 1976; )