Selection and Validation of Reference Genes for the qRT-PCR Assays of Populus ussuriensis Gene Expression under Abiotic Stresses and Related ABA Treatment

Populus ussuriensis Kom. is one of the most important tree species for forest renewal in the eastern mountainous areas of Northeast China due to its fast growth, high yield, and significant commercial and ecological value. The selection of optimal reference genes for the normalization of qRT-PCR data is essential for the analysis of relative gene expression. In this study, fourteen genes were selected and assessed for their expression stability during abiotic stress (drought, high salinity, and cold stress) and after the treatment with the drought-related hormone ABA. Three algorithms were used, geNorm, NormFinder, and BestKeeper, and a comprehensive ranking of candidate reference genes was produced based on their output. The most appropriate reference genes were UBQ10 and RPL24 for drought and ABA treatment, UBQ10 and TUB3 for cold stress, and UBQ10 and 60S rRNA for high salinity. Overall, UBQ10 was the most stable reference gene for use as an internal control, whereas PP2A was the least stable. The expression of two target genes (P5CS2 and GI) was used to further verify that the selected reference genes were suitable for gene expression normalization. This work comprehensively assesses the stability of reference genes in Populus ussuriensis and identifies suitable reference genes for normalization during qRT-PCR analysis.

Effect of Thermal Modification on the Physical Properties of Populus ussuriensis

Heat treatment is an environmental method of wood modification. The density of Populus ussuriensis, dimensional change and equilibrium moisture content change were tested through the different temperature processing, and get the influence of heat treatment process on the performance of the wood. The results show that heat treatment is an effective way to improve wood dimensional stability and shrinkage properties. With the improvement of heat treatment intensity, the equilibrium balance moisture content of wood will then gradually reduced. When treating temperature reaches 180°C above, the wood drying shrinkage properties greatly decreased, and trend to stable.

The Preservation Mechanism of Treated Populus Ussuriensis by Extract of Camphor Leaves

Populus ussuriensis has been widely used in furniture and building. However, it was easy to be decay. When it was treated by water extractive of camphor leaves, it had better effect on against decay. So it was necessary to research the preservation mechanism of it. Therefore, the water extractives of camphor leaves and the ether extractives of treated P. ussuriensis were determined by GC/MS. The results shown the main components were D-Camphor, 1, 6-Octadien-3-ol, 3, 7-dimethyl- and α-Terpineol in water extractives of camphor leaves. They were served as cardiotonic, anodyne, preservative, pesticide, so they had function of prevention. And, they also existed in treated P. ussuriensis. Therefore, the preservation mechanism was maybe known that D-Camphor, 1, 6-Octadien-3-ol, 3, 7-dimethyl- and α-Terpineol was active substance for bacteriostat. So, the water extractives of camphor leaves could be develop an environment-friendly wood preservative.