Morphology and tuber formation of in-vitro grown potato plants harboring the yeast invertase gene and/or the rolC gene

Growth and tuber formation of transgenic potato plants (Solanum tuberosum c v. Desiree) harboring the yeast invertase gene and the rolC gene individual ly or in combination under the transcriptional control of the patatin promo ter were investigated under different conditions in vitro. Plants expressin g only the invertase gene were morphologically similar to control plants. r olC transgenic plants had an increased tiller number, improved root growth, and a higher total biomass. Tuber formation and growth were altered by the introduced transgenes. The sucrose requirement to induce tubers was shifte d to lower or higher concentrations for invertase- or rolC-expressing clone s, respectively. In addition, rolC plants formed tubers of altered morpholo gy. A comparison with soil-grown plants showed that morphological parameter s can be predicted to some extent from in vitro studies, while for reliable prescreening of parameters concerning tuber formation and growth, an optim ization of currently used protocols is necessary.