Transformed potato plants as a model for studying the hormonal and carbohydrate regulation of tuberization

Wild-type plants and several transformed genotypes of potato (Solanum tuber osum L., cv. Desiree) were used to investigate in vitro tuber formation. Th e transformed plants contained the following gene constructions: the rolB a nd rolC genes under the control of the B33 patatin promoter, which evoked t he morphogenetic changes characteristic of phytohormones; the yeast inverta se gene (inv) under the control of the B33 patatin promoter affecting the c arbohydrate metabolism; and the gene for ADPglucose pyrophosphorylase (AGP) in the antisense orientation, under the control of the 35S cauliflower mos aic virus promoter. Double transformants were also used containing various combinations of the above-listed genes. The control-transformants contained the GUS gene under the 35S promoter. Exogenous phytohormones and especiall y sucrose promoted tuber formation. Tuber initiation and their subsequent g rowth were activated by various factors: cytokinin (kinetin) and sucrose at high concentrations stimulated tuber initiation, while IAA and sucrose at a moderate concentration were favorable for tuber growth. Phytohormone effe cts were most pronounced at the lowest sucrose concentration still inducing tuberization. The transformed plants harboring the B33-rolC gene produced tubers at a higher range of sucrose concentrations than the control transfo rmants. Kinetin markedly stimulated tuber initiation by this genotype, but IAA did not accelerate tuber growth. In the B33-rolB and especially the B33 -inv plants, tuberization was started at a fewer sucrose concentration. Tub er formation by the 35S-aAGP plants was especially active at a high (8%) su crose concentration. IAA did not substantially affect the size of their tub ers, and kinetin even reduced it. A comparison of in vitro tuber formation by the wild-type and transgenic plants can provide additional insights into the interaction between the hormonal and carbohydrate control of potato tu berization.