Study On Cell Wall Structural And Mechanical Properties Of C3H And HCT RNAi Transgenic Poplar

In this paper, non-transgenic, down-regulated Coumaroyl shikimate 3-hydroxylase(C3H) transgenic poplar and down-regulated hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase(HCT) transgenic poplar(Populus alba×P. glandulosa cv`84k’) was collected as experimental materials. Glycosyl Linkage Assay and Fourier Transform infrared(FTIR) spectroscopy was used to compare woody chemical composition content of non-transgenic and transgenic poplar. The fiber and cell morphology of non-transgenic and transgenic poplar were studied with Olympus BX51 optical microscope and an image analysis system. The longitudinal elastic modulus and hardness of wood fiber secondary cell wall were investigated by nanoindentation testing, changes of transgenic poplar cell wall mechanical properties was studied in the paper.The main results and conclusions were summarized as follows:(1) Down-regulation of HCT increased hemicellulose content by 8.07%, but reduced lignin content by 9.41%. Hemicellulose content decreased by 6.61%, while cellulose content increased by 10.61% after the down-regulation of C3 H. The ratios of FTIR peak heights, I1507/I1425、I1596/I1425、I1507/I895、I1596/I895、I1507/I1745 and I1596/I1745 of both HCT and C3 H transgenic poplars are slightly smaller than the wild type, but there was no significant difference between transgenic and wild type, the relative lignin content of both HCT and C3 H transgenic poplar are slightly less than the non-transgenic type. As examined from FTIR spectra, the ratio of the peaks 1372 and 2900 cm-1 of transgenic poplar are lower than the non-transgenic type.(2) Fiber cell diameter, fiber cell lumen diameter, double fiber cell wall thickness, vessel cell lumen diameter and double vessel cell wall thickness of non-transgenic poplar are 15.091 μm, 11.660 μm,3.431 μm,32.206 μm and 3.674 μm, respectively. Those of HCT transgenic poplar are 13.690 μm, 10.857 μm,2.834 μm,26.745 μm and 2.995 μm, respectively, and 14.104 μm, 10.504 μm,3.600 μm,25.873 μm and 3.559 μm for C3 H transgenic poplar. Down-regulated of HCT gene and C3 H gene significantly decreased the cell size of the fiber cell and the vessels. Tangential fiber cell lumen diameter of transgenic poplar is less than non-transgenic poplar, and there are significant differences between them. Double radial fiber cell wall thickness of HCT transgenic poplar is smaller than non-transgenic type poplar, while that of C3 H transgenic poplar is higher than non-transgenic type poplar. Cells near pith generally have higher tangential fiber cell lumen diameter than those near bark. On the contrary, Fibers near bark have higher double radial fiber cell wall thickness. Tangential vessel cell lumen diameter of non-transgenic poplar has significant differences with transgenic poplar, and greater than transgenic poplar. Double radial vessel cell wall thickness of HCT transgenic poplar is 18.5% smaller than non-transgenic type poplar, while C3 H transgenic poplar is only 3.1% smaller than non-transgenic type poplar. Gene down-regulated has a significant effect on double radial vessel cell wall thickness. The ratios of double cell wall thickness to lumen diameter of fiber and vessel of non-transgenic poplar are 0.311 and 0.121, which of HCT transgenic poplar are 0.272 and 0.119, and for C3 H transgenic poplar, those are 0.353 and 0.143. The ratios of double cell wall thickness to lumen diameter of fiber and vessel of C3 H transgenic poplar are more than non-transgenic poplar and there is significant difference between them. However, the ratios of double cell wall thickness to lumen diameter of fiber and vessel of HCT transgenic poplar are less than non-transgenic poplar, and the ratio of fiber cell wall thickness to lumen diameter of this transgenic poplar is significant different to non-transgenic type.(3) The air-dried density of non-transgenic poplar, HCT transgenic poplar and C3 H transgenic poplar are 0.366g/cm3,0.411 g/cm3 and 0.384 g/cm3, air-dried density of transgenic poplar is slightly more than non-transgenic poplar. The longitudinal hardness of wood fiber secondary cell wall of non-transgenic poplar, HCT transgenic poplar and C3 H transgenic poplar are 0.513 GPa,0.518 GPa and 0.496 GPa, that of HCT transgenic poplar are 0.1% more than non-transgenic poplar and that of C3 H transgenic poplar are 0.1% less. There are no significant differences between three types poplars. The longitudinal elastic modulus of wood fiber secondary cell wall of non-transgenic poplar, HCT transgenic poplar and C3 H transgenic poplar are 13.50 GPa,17.29 GPa and 17.18 GPa, that of HCT transgenic poplar and C3 H transgenic poplar are 28.1% and 27.3% more than non-transgenic poplar. There was significant difference between the longitudinal elastic modulus of transgenic type and non-transgenic type, but no significant difference was shown between two transgenic poplars.