Morphological characteristics of cells and main metabolic components in xylem of Cunninghamia lanceolata compression wood.

To explore the relationship between major metabolic components and the formation of compression wood (CW), we took the Cunninghamia lanceolata CW induced by bending as the study material, and then clarified the anatomic characteristics and lignin contents of C. lanceolata CW. Further we used GC-MS to indentify the major metabolic components from the developed xylem and analyzed the relative abundance. The results showed that the most of CW tracheids were oval and developed with thick cell walls. Average length and width of CW tracheids were 1 347.34 μm and 20.18 μm respectively, which were significantly less than those of opposite wood (OW). The average ratio of cell wall to lumen was 0.43, obviously higher than that of OW. The relative content of CW increased by 21.9% compared with the OW. Eighteen known metabolites and isomers could be identified at the three treatment periods, which were classified into six categories. The saccharides represented the largest group (7=monosaccharide 4 + disaccharide 3), followed by organic acid (5), alcohol (2) and amino acid (2), inorganic acid (1) and lactone (1). By the comparison of metabolite contents between CW and OW in the period I, we found that there was a slight difference in the contents of fructose and glucose; however, both fructose and glucose decreased gradually as bending treatment progressed, and their contents in CW were both less than those in OW at the period Ⅱ and Ⅲ. This was in line with the fact of cellulose content decreasing in CW. In addition, shikimic acid associated with the lignin biosynthesis was detected in this experiment. The ratio of this compound showed a rising trend as bending time prolonged, and its content in CW was obviously higher than that in OW at the period Ⅲ, which might partly explain the reason of higher lignin content in CW.