Molecular And Physiological Mechanisms Of Light And Nitrogen Regulating In The Wood Formation Of Populus Alba × P. Glandulosa

Due to the rapid economic development,the demand for wood had increased,the area of planted forests that can be harvested had decreased year by year.Therefore,the research on the regulation mechanism of wood quality and yield be carried out was siginificant to ensure the demand for wood for growing people’s lives and industrial development and ensure the rapid development of economic construction.The formation of wood was regulated by its own genes and environmental factors.Light and nitrogen were two important environmental factors that affect plant growth and wood development.However,at present,studies on the response of wood to changes in light and nitrogen were mainly focused on the study of light or nitrogen single factors,and little research had been done on the interaction between them.Moreover,the research level was mostly concentrated on the phenotypic and anatomical levels,and the research on its intrinsic molecular and physiological mechanisms was still insufficient.Therefore,in this experiment,tissue culture seedlings of Populus alba × Populus glandulosa were used as test materials for sand culture treatment,and the light and nitrogen treatment were carried out to analyze the physiological indexes such as amino acid,soluble sugar and phytohormone conten,.and transcriptional expression levels of genes involved in the phytohormone signal transduction and secondary cell wall synthesis were also analyzed,and the following results were obtained.(1)Compared with the control light,high light promoted the high growth and radial growth of P.alba × P.glandulosa,which increased the net photosynthetic rate of leaves and the soluble sugar content.Compared with normal nitrogen,low nitrogen treatment promoted the root growth of P.alba × P.glandulosa,but inhibited high growth and radial growth,reduced the enzyme activity of nitrogen metabolism,and reduced the absorption and accumulation of nitrogen by plants.High nitrogen treatment inhibited the root growth of P.alba × P.glandulosa,improved the net photosynthetic rate of P.alba ? P.glandulosa,increasedthe enzyme activity of nitrogen metabolism,and promoted the absorption and accumulation of nitrogen by plants.(2)Compared with the control lght,high light reduced the lumen diameter and the length of the vessel element and the thickness of the fiber cell wall in P.alba × P.glandulosa wood.High light increased the content of mannose,glucose and galactose in the hemicellulose,decreased the content of rhamnose and galacturonic acid in the hemicellulose.Compared with normal nitrogen,low nitrogen treatment resulted in a significant increase in the thickness of the secondary cell wall and the length of the fiber,and the lumen diameter of the vessel element and the diameter of the fibroblasts were significantly reduced.High nitrogen supply resulted in the lumen diameter of the vessel element and the diameter of the fibroblasts were significantly increased,and the thickness of the secondary cell wall and the length of the fibers were significantly reduced.Compared with normal nitrogen,low nitrogen treatment led to decrease in the content of lignin,and increased the content of mannose,glucose and arabinose which constituted hemicellulose.High nitrogen increased the content of lignin,reduced the content of mannose and glucose which constituted hemicellulose.(3)Compared to control light,high light inhibited the transcriptional expression of genes involved in plant hormones,glycosyltransferases,and cell wall formation.High light led to the significant decrease in the contents of ABA and IAA in wood,which may be related to the down-regulated expression of ABA1 and CCD7.They were involved in ABA and IAA synthesis in wood response to high light.High light caused the decrease in the thickness of the cell wall of P.alba × P.glandulosa,which may be related to the down-regulated expression of the cell wall-forming genes FLA12,XTHs,AZF2,4CEL1 and so on.Compared with normal nitrogen,low nitrogen led to secondary cell wall thickening,which may be related to the transcriptional up-regulation of wood formation related genes MYB3,UGT74F1 and UGT84A1.High nitrogen led to increase the contnet of lignin in wood,which may be related to the transcriptional up-regulation of genes LAC2 and OMT1.The above results indicated that high light promoted high growth and secondary growth of plants,but reduced the length of the fibers and the thickness of the cell wall.High nitrogensupply promoted high growth and secondary growth of plants,but reduced the length of the fibers and the thickness of the cell wall.Low nitrogen treatment inhibited high growth and secondary growth of pants,promoted the elongation of the fiber and thickening of the cell wall.The formation of poplar wood is regulated by plant hormones and its own genes,which may be related to the transcriptional expression levels of related genes under high light and different nitrogen conditions.In the production practice,under the premise of ensuring the wood properties,it was possible to promote the growth and development of poplar and increase the yield of wood by appropriately increasing the light intensity and nitrogen supply level within a certain range.