Studies On Rhythms Of Vascular Cambial Activity And Cell Development In Koelreuteria Bipinnata Franch

Wood (secondary xylem) is a product of cambium activities which determines timber production and the structure and properties of wood. So studying the origin and development of cambium is not only an important foundation on theoretical issues of developmental biology and forestry, but the basis of the molecular biology research. Specific studies were as follows:The apical meristem of Koelreuteria bipinnata Franch belongs to "tunica-corpus" structure. Generally, sprout has budded in late February, completed at the end of April.The apical meristem structure of Koelreuteria bipinnata belongs to "tunica-corpus" structure. The development buds usually start in late February and mainly completed at the end of April. Procambium bundle of the third and fourth internode of Koelreuteria bipinnata annual branches are differentiated into primary vascular. In addition, formative cells of Koelreuteria bipinnata appears to telescoped type.The cambium of Koelreuteria bipinnata shows seasonal periodicity. Cells of cambium usually recovered before the buds germination in spring.With the development of leafy cotyledon and shoots, the cambium cells increased apparently in the middle of April. Then, cambium are activity in the beginning of May and the layer number of cells reached 5-7, but its level recovered to the middle of April. The cell radical wall of the cambium enlarged and secondary wall began to thicken. After the middle of October, the cambium entered period of dormancy. The layer cells maintained in two to three and then recovered to develop since the spring.About a week of cotyledon expansion, the immature phloem cells are formed with wall thinner and ordered irregularly. The early phloem are differentiated into sieve tubes, companion cells, and parenchymal cells during the beginning of March and May for about two months. The differentiation of early phloem is two weeks earlier than the xylem and production of phloem fiber at the beginning of May. The advanced stage of the phloem are during at the beginning of May to the middle of September, and then the cambium differentiated into sieve cells, companion cells, axial parenchyma cells, ray parenchyma cells, and wood fibers. The development of phloem is usually completed at the end of October and the dividing line is not obvious compared with xylem.The secondary xylem has produced one to two layers of early catheter and wood-fiber cells. The formation of springwood needs about two months from middle of the March to May. However, the laterwood are formed at the beginning of June to the end of October about four months. The layers of immature xylem cells increased rapidly in June and the radical of xylem reached maximum width at the end of August. The total number of xylem cells kept on growing since September 21. At the beginning of November, the cambium is entered into resting stage. Subsequently, the secondary wall of xylem began thickening and lignification.The polysaccharide particles seasonal variation of Koelreuteria bipinnata are classified into four steps, and disappeared during cambium recovered to the vigorous stage, and then increased for late stage. However, the polysaccharide particles disappeared again during the late stage changed into resting stage, and increased once more since then until recovered to activation of cambium in spring.In this study, the length, width, length-width ratio, lumen diameter, of fiber and catheter, and the difference of double wall thickness of Koelreuteria bipinnata cambium during the activity stage by quantitative anatomy and microscopic image analysis system. The result also showed that the cambium cell layers are associated with indicators about wood fiber and conduit. In addition, the width of fusiform initial are related with the fiber length and catheter lumen diameter of conduit.Fluorescence microscope and histochemical stain was conducted to identify the lignification process of Koelreuteria bipinnata. There’s no fluorescence signal of the first round of the catheter, which differentiated by vascular cambium at the recovered early stage, but strengthened than the round tissue about a half month later indicating that the lignification of catheter are faster than the round cells. The cambium become activity during May to July and the xylem becoming lignification. During September and October, the activity stage of cambium transformed into the period of dormancy and the fluorescence distributed uniformity, accompanied with the lignin deposition.In addition, the fluorescence of springwood cell wall perform weak contrast with strengthen in the summerwood.