Agrobacterial rol genes modify thermodynamic and structural properties of starch in microtubers of transgenic potato

Wild-type (WT) plants of potato (Solanum tuberosum L.) and their transgenic forms carrying agrobacterial genes rolB or rolC under the control of B33 class I patatin promoter were cultured in vitro on MS medium with 2% sucrose in a controlled-climate chamber at 16-h illumination and 22A degrees C. These plants were used as a source of single-node stem cuttings, which were cultured in darkness on the same medium supplemented with 8% sucrose. The tubers formed on them were used for determination of the structure of native starch using the methods of differential scanning microcalorimetry (DSC), X-ray scattering, and scanning electron microscopy. It was found that, in starch from the tubers of rolB-plants, the temperature of crystalline lamella melting was lower and their thickness was less than in WT potato. In tubers of rolC plants, starch differed from starch in WT plants by a higher melting temperature, considerably reduced melting enthalpy, and a greater thickness of crystalline lamellae. Deconvolution of DSC thermogram makes it possible to interpret the melting of starch from the tubers of rolC plants as the melting of two independent crystalline structures with melting temperatures of 65.0 and 69.8A degrees C. Electron microscopic examination confirmed the earlier obtained data indicating that, in the tubers of rolC plants, starch granules are smaller and in the tubers of rolB plants larger than in WT plants. Possible ways of influence of rol transgenes on structural properties of starch in amyloplasts of potato tubers are discusse

Thermodynamic and structural properties of tuber starches from transgenic potato plants grown in vitro and in vivo

Potato plants harboring Phytochrome B (PHYB) gene from Arabidopsis thaliana or rol genes from Agrobacterium rhizogenes were used to study the effect of transgene expression on structure and properties of starch in tubers. Thermodynamic characteristics of starch (melting temperature, enthalpy of melting, thickness of crystalline lamellae) were shown to be variable depending on the transgene expression and plant culturing mode: in vitro or in soil. The expression of rolB or rolC genes in in vitro cultured plants evoked opposite effects on starch melting temperature and crystalline lamellae thickness. AtPHYB or rolB expression in the soil-grown potato led to the formation of more defective or more ordered starch structures, respectively, in comparison with starches of the same lines grown in vitro. On the whole, our study revealed genotype-dependent differences between starches extracted from tubers of in vitro or in vivo grown plants