Tuber morphology and starch accumulation are independent phenomena: Evidence from ipt-transgenic potato lines

Tuber formation and carbohydrate metabolism in potatoes were studied using transgenic potato plants carrying the Agrobacterium tumefaciens ipt gene, i nvolved in cytokinin biosynthesis. Three independent transformants, viz, cl ones 1, 11 and 13, whose cytokinin acid auxin content had previously been s hown to be different from each other and from the wild-type, were analysed in vitro. Clones 11 and 13 showed a higher ability to form stolons and tube rs, as evident from: (1) stolon development in whole plants grown under non -inductive conditions, (2) total number and weight of tubers formed by cutt ings of this clone in darkness, (3) tubers appeared earlier than tubers of, wild-type plants and at a lower sucrose concentration in the medium, Clone 1 did not form stolons or tubers under any conditions tested, but rather fo rmed short shoots. A series of metabolic changes, known to be characteristi c for tubers, were analysed in lea,es, stems and developing buds. It was fo und that the short type of shoots, formed by clone 1, had metabolic charact eristics very similar to tubers formed in wild-type or clones 11 and 13, in cluding glucose, fructose, sucrose, and starch levels, and activities of in vertase, sucrose synthase and fructokinase. It is concluded that the regula tion of the stolen swelling and of carbohydrate! metabolism, normally occur ring simultaneously, can be uncoupled, and are thus, at least partly indepe ndent phenomena. The present data obtained with a high-cytokinin line indic ate that cytokinins (probably in concert with auxins) might he mainly invol ved in the regulation of tuber morphology.