Effect of <Emphasis Type="Italic">Rol</Emphasis> Transgenes,IAA, and Kinetin on Starch Content and the Size of Starch Granules in Tubers of <Emphasis Type="Italic">In Vitro</Emphasis> Potato Plants

Stem cuttings were produced from Solanum tuberosum L., cv. Desiree, plants and their transgenic forms harboring rolB and rolC genes from Agrobacterium rhizogenes. Plants were cultured on hormone-free Murashige and Skoog nutrient medium (MS) and on MS supplemented with IAA or kinetin. In microtubers developed on these cuttings, we estimated the content of starch and the number and size of starch granules. Expression of rol genes changed these indices: in tubers of rolC transformants, a greater number of small granules were produced, whereas in tubers of rolB transformants, a fewer number of large granules were developed as compared with wild-type plants. Expression of rol genes did not affect starch content during the first three weeks of cutting culturing but increased it by 15–30% in five-week-old tubers. IAA addition to MS medium increased starch content and the size of starch granules in control plants and rolB tubers by 10–30%, whereas kinetin did not exert any significant influence. The effects of rol transgenes on the initiation and termination of starch granule development are discussed.