Study On The Regulation Of Exogenous IAA And GA₃ To Tension Wood Formation In Hybrid Poplar （Populus Deltoids ’Lux’×Populus Deltoides ’Harvord’）

Poplar is one of the excellent species of planted fast-growing forestry and the main raw materials for wood processing and utilization,the wood is widely used in the industries of papermaking,artificial board and furniture,which has made outstanding contribution for the development of the forestry industry in our country.However,the wood from the upper side of the inclined hybrid poplar stems,branches and even erect trunks often contain a lot of tension wood which is one of the main wood defects and seriously restrict the utilization of hybrid poplar wood and the development of relevant industries.Therefore,if the mechanism of tension wood formation were figured out will be conducive to fundamentally solve the problem that the property of hardwood is often affected by this defect.In this paper,the hybrid poplar seedlings and branches growth under natural or controllable condition are used as the research object.The first study on the effect of exogenous IAA and GA₃ on the formation of tension wood is through observing changes of the growth and anatomical characteristics of the artificially inclined hybrid poplar branches and seedlings treated with different concentrations of exogenous IAA and GA₃.Then study on the regulation of exogenous hormone to the composition of wood cell wall is by observing the alterations of growth,anatomical characteristics,the expression level of genes involved in polar auxin transport and cellulose biosynthesis in erect hybrid poplar seedlings treated with IAA or NPA as well as exploring the mutual relevance of plant hormone treatment,related gene expression,cell wall composition and tension wood formation,and as a consequence,trying to reveal the regulation mechanism of exogenous hormone to tension wood formation in hybrid poplar.In addition,there are explorations of the methods for determining the endogenous IAA content in hybrid poplar by HPLC and measuring G-layer area ratio with ImageJ software.The results are as follows:1.Effects vary in treatments with different concentrations of exogenous IAA and GA₃,there is no obvious effect with the treatment of low concentration IAA（0.01 mg·g-1）,whereas the growth and tension wood formation in tilted hybrid poplar branches and seedlings are inhibited by exogenous IAA in high concentration（1 mg·g-1）.In contrast,the growth and tension wood formation in tilted hybrid poplar branches and seedlings are promoted by low concentration GA₃（0.1 mg·g-1）and the effect is more significant with high concentration GA₃（10 mg·g-1）.2.The effect of the combination of exogenous IAA（0.01 mg·g-1）and GA₃（10 mg·g-1）is stronger than that of applying the two hormones alone,suggesting that exogenous IAA and GA₃ can induce the growth and tension wood formation of hybrid poplar together and a certain level of IAA/GA₃ should play a key role in this physiological process.3.Exogenous IAA（10 mg·g-1）can promote the growth and the expression of related genes involved in polar auxin transport（AUX2,PIN1 and ABCB1）and cellulose biosynthesis（CesA5,CesA13,UGP1 and UGP2）in upright hybrid poplar,thus inducing the formation of tension wood.NPA decreases the expression of PIN1,CesA4,CesA7,CesA8,CesA17 and CesA18,efflux of cellular auxin and cellulose biosynthesis,thus restraining the growth of seedlings,and no tension wood formed.Accelerating intercellular polar auxin transport should be a crucial physiological processe of inducing formation of tension wood.4.The methods both determining of endogenous IAA in hybrid poplar by SPE-HPLC and measuring the G-layer area ratio with ImageJ software is preliminary established.