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

Abstract

INTRODUCTIONTuber formation in potato is regulated by numerous external and internal factors with phytohormones being of special importance [1]. In order to investigate the hormonal control over tuber formation, some researchers used transformed potato plants expressing rolB and rolC genes of Agrobacterium rhizogenes [2]. Biochemical mechanism of the operation of rol trans genes remains debatable; however, it was shown that their role in higher plants resembles to the effect of phytohormones: auxins in case rolB and cytokinins in case rolC [3]. It is assumed that hormone like effect of rol genes may be related to their influence on the metabolism of auxins and cytokinins or to the changes in plant cell sensitivity to these phytohormones [3]. It was also shown that the intensity of the effect of rol genes on morphogenesis of potato plants greatly depends on the used promoter governing organospec ificity of gene expression [4].It order to investigate the effect of genes rolB and rolC on tuber formation, we used B33 class I patatin promoter, which ensured preferred expression of B33::rolC and B33::rolB in growing potato tubers [5]. These experiments showed that transgenes induced numerous morphological changes accompanied by changes in the activity of some enzymes of carbohy drate metabolism, the content of soluble sugars [6], and the number and size of starch granules [7]. The obtained data suggested that transgenes rolB and rolC might also modify qualitative characteristics of storage starch, which by volume and biological role is the Abstract-Wild type (WT) plants of potato (Solanum tuberosum L.) and their transgenic forms carrying agro bacterial 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 22°C. These plants were used as a source of single node stem cuttings, which were cultured in darkness on the same medium supple mented 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 dif fered 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 69.8°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 star...

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

“…As regards our starch samples, the melting temperature increased in KCl solution by 1.8-2.2 • K, values typical for B-type of a polymorphic structure. Together with previous WAXS data (Aksenova et al, 2010;Wasserman et al, 2014), this indicates that the polymorphic starch structure did not change in transgenic plants under different growth conditions.…”

“…However, we have previously shown by Х-ray scattering and DSC that such a change was not observed in case of rol transformants (Aksenova et al, 2010). Also the expression of AtPHYB did not change the polymorphic structure of starches.…”

Techno-commercial Aspects of Relevance to Red Beet

“…The in fl uence of rol genes on carbohydrate metabolism has seldom been studied, even in other plant systems. When rolB and rolC gene-transformed potato microtubers were analyzed, the structure of the starch granules were very different in each case from those of normal tubers (Aksenova et al 2010 ) , indicating the commercial importance of such gene interactions. The selective secretion of proteins such as peroxidase enzymes from red beet hairy roots (Thimmaraju et al 2005(Thimmaraju et al , 2007 has demonstrated the inherent secretory nature, which is yet another phenomenon worth characterizing for commercial exploitation in the context that hairy roots ably synthesize human proteins and other animal proteins (Kang et al 2011 ;Guillon et al 2006 ) .…”