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Abstract
Wild-type potato (Solanum tuberosum L.) plants and their transformants harboring agrobacterial rolB or rolC genes under control of the patatin class I promoter were cultured in vitro. These plants were used as a source of single-node stem cuttings. The structure of native starch in tubers formed on cuttings was determined using methods of X-ray scattering and differential scanning microcalorimetry (DSC). It was found that in starch from tubers of rolB plants the melting temperature of crystalline lamella was lower and their thickness was less than that in wild-type potato. In tubers of rolC plants starch differed from starch in wild-type plants by a higher melting temperature, reduced melting enthalpy, and a greater thickness of crystalline lamellae. The melting of starch from tubers of rolC plants proceeded as the melting of two independent crystalline structures with melting temperatures of 338.0°K and 342.8°K. Overall data show that starches of different structure can be obtained by using transgenic approach.
Highlights
The transition to tuber formation in potato depends on certain environmental and internal cues
Tuber-specific expression of rol transgenes was accompanied by changes in the pattern of tuber formation, including the shape of tubers, their size and number, anatomic structure, phytohormone content and carbohydrate metabolism, that are in correlation with our previously data [10,22,23]
As to starch content calculated per g of dry weight, there were no appreciable differences between tubers wild type and rolB plants, whereas in tubers of rolC plants the level of starch was slightly decreased
Summary
The transition to tuber formation in potato depends on certain environmental and internal cues. Numerous studies showed that phytohormones as internal factors markedly affected all stages of tuberization [3,4,5]. Agrobacterium rhizogenes rolB and rolC transgenes were used by some researchers to simulate the hormonal control over tuber formation in transformed potato plants [6]. Molecular mode of action of rol transgenes remains debatable; it was shown that their effects on higher plants were reminiscent to the effect of phytohormones: auxins in case rolB and cytokinins in case rolC [6]. It was suggested that hormone-like effect of rol genes may be related to their influence on the metabolism of auxins and cytokinins or to changes in cell sensitivity to these phytohormones [7]. It was shown that the amplitude of the rol gene effect on defined plant organ greatly depended on the used promoters, especially in case of tissue-specific ones [8]
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