| Previous studies have shown that the down-regulation of C3H and HCT genes can reduce lignin content and cause the change of monomer ratio,but the effect of chemical component change on the transgenic poplar structure and properties and the effect differences between the both genes are still unclear.In this paper,non-modified poplar?Populus alba×P.glandulosa cv`84k'?,down-regulated Coumaroyl shikimate 3-hydroxylase?C3H?transgenic poplar and down-regulated hydroxycinnamoyl CoA:shikimate hydroxycinnamoyl transferase?HCT?one-year-old transgenic poplar were collected as experimental materials.Optical microscope,Nitrogen Adsorption Desorption?NAD?,X-ray diffraction?XRD?,Acetyl Bromide Assay,2D HSQC NMR,Nano indentation?NI?tests and other advanced structure and performance characterization methods were used to study the changes of microscopic structure,chemical composition,cell wall density and cell wall mechanical properties of C3H and HCT transgenic poplar.The effects of cell wall structure?Including the structure and chemical composition?change of C3H and HCT transgenic poplar on their properties were revealed.Moreover,the effects of two genes on structure and performance were compared.All above provided the basic data for early evaluation of both transgenic poplar wood properties.The main results and conclusions were summarized as follows:?1?Growth properties and vessel number per unit area of transgenic poplar saplings.The down-regulated C3H and HCT genes slowed down the growth of trees,the stem diameter of C3H transgenic poplar and HCT transgenic poplar was significantly decreased by 9.6%and 8.3%,respectively?P<0.05?.The vessel number per unit area of C3H transgenic poplar and HCT transgenic poplar was significantly decreased by 6.5%and 5.2%,respectively?P<0.05?.?2?Cell wall area ratio and pore structure of transgenic poplar saplings.The cell wall area ratio of non-modified poplar,C3H transgenic poplar and HCT transgenic poplar were 40.27%,45.10%and 43.71%,respectively.The cell wall area ratio of C3H transgenic poplar was increased by 12.0%and HCT transgenic poplar was increased by 8.5%,and the differences were significant at the level of P<0.05.The BET specific surface area of non-modified poplar,C3H transgenic poplar and HCT transgenic poplar were 0.6266 m2·g-1,1.7247 m2·g-1 and 0.7141 m2·g-1,respectively.The BET specific surface areas of two transgenic poplars were significantly higher than that of non-modified poplar?P<0.05?.?3?Cellulose crystal structure of transgenic poplar saplings.The cellulose crystallinitys of both transgenic poplars were significantly higher than that of non-transformed poplar?P<0.05?,C3H transgenic poplar and HCT transgenic poplar were 18.5%and 16.1%larger than non-modified poplar,respectively.The microcrystalline widths of cellulose were also increased by 7.5%and6.4%,respectively,and the differences were significant at P<0.05.?4?Chemical composition of transgenic poplar saplings.Preliminary analysis by FTIR found that the characteristic bands ratio I1507/I1382 and I1507/I89595 of the transgenic poplar were significant lower than the non-modified poplar?P<0.05?.It confirmed that the lignin content of transgenic poplar was lower after the genetic modification.And then lignin content of transgenic poplar saplings were selective analyzed by the method of Acetyl Bromide Assay,the lignin content of both transgenic poplars decreased markedly,the lignin content of C3H transgenic poplar decreased from21.11%to 14.80%,and that of HCT transgenic poplar decreased from 21.11%to 16.82%,and the differences were significant at P<0.01.At last,mainly chemical composition was analyzed by the monosaccharide compositional analysis.It found lignin content of two transgenic samples decreased significantly.Mannose?Man?contents of both transgenic poplars were lower by 17.2%compared with the non-modified poplar.In addition,Galactose?Gal?content of C3H transgenic poplar increased significantly while that of HCT transgenic poplar decreased.Glucose?Glc?content of the C3H transgenic sample decreased sharply.Moreover,the cellulose content of C3H transgenic poplar increased significantly.All above changes were statistically significant at the P<0.05.?5?Lignin structure and monomer ratio of transgenic poplar saplings.Non-modified poplar and transgenic poplar lignin contained?-O-4?aryl ether linkages and their derivative substructures,resinol substructures,spirodienone substructures,phenylcoumarane substructures,p-hydroxycinnamyl alcohol end groups,syringyl units,p-hydroxyphenyl units,guaiacyl units,p-hydroxybenzoate substructures and ferulate.Down-regulated C3H and HCT reduced the?-O-4relative content of poplar.The S unit,H unit and S/G of C3H transgenic poplar increased while its G unit decreased.The S unit and S/G of HCT transgenic poplar decreased while its G unit increased.?6?Cell wall basic density and cell wall mechanical properties of transgenic poplar saplings.The cell wall basic density of non-modified poplar,C3H transgenic poplar and HCT transgenic poplar were 0.688 g·cm-3,0.579 g·cm-3 and 0.650 g·cm-3,respectively.Cell wall basic density decreased significantly in both C3H and HCT transgenic poplar?P<0.05?.The longitudinal elastic modulus of wood fiber secondary cell wall of non-modified poplar,C3H transgenic poplar and HCT transgenic poplar samplings without resin permeated were 16.04 GPa,16.99 GPa and 17.18GPa,that of C3H transgenic poplar and HCT transgenic poplar were 5.9%and 7.1%more than non-modified poplar.There was significant difference between the longitudinal elastic modulus of transgenic type and non-modified type at P<0.05.The longitudinal hardness of wood fiber secondary cell wall of non-modified poplar,C3H transgenic poplar and HCT transgenic poplar samplings without resin permeated were 0.528 GPa,0.474 GPa and 0.527 GPa,that of C3H transgenic poplar and HCT transgenic poplar both were less than non-modified poplar.There was significant difference between the longitudinal hardness of C3H transgenic poplar and non-modified poplar?P<0.05?.?7?Effects of cell wall structure on cell wall basic density and mechanical properties of poplar samplings.The increase of pore structure and the decrease of lignin content lead to the decreases of cell wall basic density of both transgenic poplars,the correlation coefficients were 0.9614 and-0.9295,respectively.The longitudinal elastic modulus of wood fiber secondary cell wall of both C3H transgenic poplar and HCT transgenic poplar samplings were increased with the increase of cellulose crystallinity,crystallite size and holocellulose content,the correlation coefficients were0.9624,0.9566 and 0.9207,respectively.The longitudinal hardness of cell wall of poplar samplings were negatively correlated with BET specific surface area and positively correlated with cell wall basic density,the correlation coefficients were-0.9714 and 0.9446,respectively.The decrease of cell wall hardness of C3H transgenic poplar and HCT transgenic poplar was mainly caused by the increase of BET specific surface area and the decrease of cell wall density.?8?Properties comparison of C3H transgenic poplar and HCT transgenic poplar.For the larger cell wall ratio,larger BET specific surface area,higher cellulose content,less lignin content and larger S/G value than HCT transgenic poplar,the C3H transgenic poplar can be more suitable for production of cellulose materials and biomass energy in later utilization. |
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