Caecal fermentation in rats fed diets containing transgenic potato tubers

Caecal fermentation in rats fed diets with 40% autoclaved potato tubers was examined. The potato tubers of the conventional cultivar, Irga, somaclone Irga, and four transgenic lines with genetically improved resistance to a necrotic strain of potato virus Y (PVY ) were compared. As regards the analysed indices, tubers of transgenic clone RIF (truncated gene coding PVY N polymerase in sense orientation), R2P (truncated gene coding PVY N polymerase in antisense orientation), and NTR1.16 (non-translated regions of the PVY N genome in sense orientation) were similar to tubers of the conventional cultivar Irga. Tubers of transgenic clone NTR2.27 (non-translated regions of PVY N genome in antisense orientation) increased the amount of caecal digesta and production of SCFA compared with tubers of the conventional cultivar and other transgenic clones. K.EY WORDS: genetically modified potato, caecum, short-chain fatty acids, rat


INTRODUCTION
The first Polish transgenic clones resistant to a necrotic strain of potato virus Y (PVY N ) were obtained in the last decade (Chachulska et al., 1997).The results of our earlier studies indicate that genetically modified potato did not differentiate animal growth and feed utilization (Zduńczyk et al., 2004a) as well as serum enzymes and indices of non-specific defence of rats (Zduńczyk et al., 2004b), compared with non-transgenic tubers.The purpose of this study was to evaluate the potential influence of the transgenic potato on the fermentation processes in the caecum of rats.

MATERIAŁ AND MTHODS
The transgenic lines of potato that were transformed with viral genome sequences in order to improve their resistance to a necrotic strain of potato virus Y (PVY N ) were prepared at the Institute of Biochemistry and Biophysics of the Polish Academy of Sciences (Chachulska et al., 1997).Four transgenic clones: R1F and R2P (transgenic lines with a truncated gene coding PV Y N polymerase in sense or antisense orientation, respectively), NTR1.16 and NTR2.27 (transgenic lines with non-translated regions of PVY N genome in sense or antisense orientation, respectively) were compared with the conventional cultivar Irga and a non-transgenic somaclone (Irga w.t.).The autoclaved (121 °C, 1013 hPa, 15 min) and dried (40°C) potato tubers were introduced in a high amount (40%) to diets, which were used in a 3-week feeding experiment on rats.Each diet contained about 9.3% crude protein in air-dry matter (5.3% of casein and 3.6% potato protein), potato and maize starch (about 27 and 36%, respectively), and standard minerał and vitamin mixtures.Samples of fresh caecal digesta obtained from 8 animals in each group were analysed.The caecal pH was measured using a microelectrode and a pH/ION meter (model 301, Hanna Instruments).The content of short-chain fatty acids (SCFA) was determined by gas chromatography (Shimadzu GC-14A with a 2.5 m x 2.6 mm glass column, containing 10% SP-1200/1% H,P0 4 on 80/100 Chromosorb W AW, column temperaturę 110°C, detector FID temperaturę 180°C, injector temperaturę 195°C).The results were statistically evaluated using one-way ANOYA and Duncan's multiple rangę test.

RESULTS
The weight of caecal digesta of rats fed diets with tubers of transgenic clone NTR2.27 was significantly higher than in the groups receiving Irga w.t. and RIF (Table 1).The lowest hydration of caecal digesta was found in groups R2P and NTR1.16, while the highest was in group RIF The highest amount of dry matter in the caecum was found in group NTR2.27.The caecal pH in group NTR1.16 increased, especially in comparison with non-transgenic Irga w.t.The lowest concentration of SCFAs in the caecal digesta was found in group R2P, and the highest one, in group Irga w.t.(Table 2).A similar distribution of SCFA concentrations was also found for C 2 , C 4 and C 5 acids.No significant differentiation was observed in the concentrations of C 3 acids in particular groups.The lowest values of the total SCFA pool size and of the major acids (C 2 -C 4 ) were found in the R2P group, while the highest values of the total SCFA pool and individual acids were determined in rats fed a diet supplemented with the NTR2.27 line.

DISCUSSION
The results of a few in vivo experiments of other authors (Hashimoto et al., 1999;Rogan et al., 2000;Zduńczyk et al., 2004a,b) indicate that tubers of potato with genetically improved virus-or insect-resistance were nutritional equivalents of their conventional counterparts.In the presented study tubers of the conventional cultivar Irga and transgenic clones RIF, R2P and NTR1.16 exerted a similar influence on the fermentation processes in the caecum of rats.However, a diet with tubers of transgenic clone NTR2.27 significantly increased the amount of caecal digesta, dry matter content and total SCFA pool.This may point to decreased utilization of nutrients (mainly starch) in the upper part of the gastrointestinal tract and/or to an increase in the activity of caecal microflora in this group of rats.The results obtained in a relatively short feeding experiment (3 weeks) are insufficient to explain the reasons for the determined differences: increased bulk of caecal digesta and total SCFA pool in group NTR2.27, as well as the highest hydration of caecal digesta in group RIF.

CONCLUSIONS
As regards their influence on caecal fermentation processes in rats, tubers of transgenic clone R1F, R2P, and NTR1.16 were similar to tubers of the conventional cultivar Irga.In contrast, tubers of transgenic clone NTR2.27 increased the bulk of caecal digesta and production of SCFA.