Improving Pulping Property By Downregulation Of Lignin Biosynthesis In Poplar

Lignin is a phenolic polymer and plays important roles in plants,but is the main resource of papermaking pollution.Thus there is of economical and environmental interests in cultivating materials with genetically modified lignin for pulping industry.The effect of F5H overexperssion and CCoAOMT downregualtion,which are in the lignin biosynthesis pathway,were studied in this paper.The following are the main progress.1.Transgenic poplar(Populus tremula×Popμlus alba) with antisense CCoAOMT was planted in field for four years.The Klason lignin content evaluation showed that the transgenic tree had a lignin content decreased by about 13%comparing to the wild control,which means that the decrement of lignin content was maintained in 4-year-old transgenic poplar.The lignin structure analyses by Thioacidolysis and GC displayed that G/S ratio in transgenic poplar was slightly decreased by about 2%comparing to control;Histology examination of stem section showed that most of vessels in transgenic tree were regular similar to that in wild control,but some vessels in transgenic trees were deformed with inward sunk walls;There were no difference in plant height and stem diameter between transgenic trees and wild control during four years of growing.2.Fiber quality evaluation showed that density,fiber width,Runkel ratio and cell wall thickness of YAPCOA38 were slightly higher than those of control.YAPCOA38 had a slightly smaller lumen diameter,which is consistent with its bigger density.YAPCOA38 had a slightly higher distribution frequency of long-length fiber(over 0.61mm) than that of control.Kraft pulping at laboratory scale was done to the transgenic and wild contro poplar.The pulp yields and cellulose degrees of polymerization of YAPCOA38 were significantly higher than those of wild control.The pulps of YAPCOA38 had lower Kappa numbers than those of control under all conditions,which means that YAPCOA38 had a less resistance to Kraft delignification.The results from evaluation of handsheets indicated that the handsheets produced from YAPCOA38 pulp had significant higher tear index than that of wild control,which means that it had better mechanical properties than wild control.Also,the brightness of YAPCOA38 handsheets had a significant higher value than that of control.The results demonstrate the improvement of quality of handsheets made from transgenic poplar(YAPCOA38).All these data demonstrated that decreased lignin content improved the pulping property,including increased pulping yield,easier delignification and higher cellulose DP. 3.We isolated the whole F5H cDNA using RT-PCR and constructed vector expressing both sense F5H and antisense CCOAOMT.With vector,the transgenic tabacco and poplar(Populus tremula×Populus alba) was obtained.PCR and Southern analysis demonstrated that both sense F5H and antisense CCoAOMT are integrated into the tobacco genome successfully.We got 29 positive clones of transgenic poplar(Populus tremula×Populus alba).