Abstract:

Objective: Wood formation is mainly controlled by the number of cambium cell division, which determines the biomass production and wood quality. The differentiation from cambium cell to mature xylem as the main line, this article discussed the wood formation processes of Pinus elliottii with aims to provide scientific guidance for the tree growth development, wood genetic improvement and wood resourse utilization of P. elliottii plantation. Method: In this paper, we mainly used transmission electron microscope (TEM) to investigate the activity regularity of cambium in detail during the wood formation of P. elliottii at the cellular ultrastructure level. Result: P. elliottii underwent annual cycles of cambial during periods of cambial activity and dormancy. The appearance of dividing fusiform cells in cambium indicated that the cells broke dormancy into recovery activity. From the end of February to the end of March, the period of transition from dormancy to activity, namely the recovery period, some autolysis occurred in the radial walls of the cambial cells, especially at the cell wall junctions. At this time, there was no significant difference between the radial wall and the tangential wall of the cambium fusiform cells that showed oval or nearly round. During the activity period from the beginning of April to the end of October, the whole cambial fusiform cells were highly vacuolated and the cell shape became irregular, both the radial wall and the tangential wall became thinner, the tangential wall was thinner and inconspicuous, the lipid droplets and starch granules decreased dramatically. The cambial activity reached the strong active phase in mid-June, the number of cells in the cambium was significantly increased and the secondary wall began to thicken. At this time, the protoplasts basically disintegrated and disappeared. The cells were dormant at the end of October to the end of the next year, the number of layers of cambium was significantly reduced, only contained 1-2 layers of thick-walled fusiform cells, the radial wall and tangential wall of the fusiform cells were significantly thickened and the inclusions of the cells began to accumulate. During the entire active period, the radial wall was significantly thicker than the tangential wall, while the differences were more obvious during the dormant period. A notable feature of the cells at the onset of cambial activity was the thinning of the cell wall, especially the radial wall. There were pine needles falling during the whole growing season and new pine needles were produced during the dormancy period, indicating that there was no obvious correlation between pine needle production and shedding and dormancy and activation of the cambial cells. The mature ray cells in the secondary xylem always contained more inclusions, and the protoplasts did not show any recession, indicating that the ray parenchyma cells maintained a high activity even after lignification for several years. Conclusion: There is a clear annual cycle of cambial for slash pine, with periods of cambial activity and dormancy. From the end of February to the end of March, it is a recovery period, and the activity period is from the beginning of April to the end of October, which is the period of slash pine wood formation. The cambial activity reaches the strong active phase in mid-June, the number of cells in the cambium is significantly increased and the secondary wall begins to thicken. The cells are dormant at the end of October to the end of the next year, the number of layers of cambium is significantly reduced, only contains 1-2 layers of thick-walled fusiform cells. In different periods of cambial activity, there are significant differences in number of layers of cambium, the radial wall and tangential wall of the fusiform cells and its cell inclusions.

Key words: Pinus elliottii, cambium, the recovery period, active period, dormancy period, cambial cell, ultrastructure, wood formation