Study On The Developmental Biology Of Fiber In The Culms Of Phyllostachys Edulis

Phyllostachys edulis (Carr.) H. De Lehaie (Moso) has the largest distribution area and the highest economical value in China. It is widely used for making furniture, construction, pulp and other industries. The study of fiber structure is a basis for revealing the mechanical properties of bamboo. By using several methods and technologies of cell and molecular biology, the initiation and development of fiber in Moso culm was first systematically studied. In this work, the origin and development mode of fiber were elucidated in detail, and the mechanisms of fiber wall formation and programmed cell death and the long-lived characteristic were also discussed. The main conclusions were as follows. 1. Fibers originate from the same procambium as the vascular bundle elements like vessels, sieve tubes and parenchyma cells, but their differentiation is later. Then they would undergo centrifugally differentiation and development from vascular bundle outwards till the fiber cap formed. The developmental process of fibers could be divided into three continual stages such as fiber initial formation and the formation of primary wall and secondary wall. During primary wall formation, fiber underwent successively co-growth with vascular bundle and intrusive growth. With the formation of secondary wall, fiber wall underwent continual thickening with aging. In the former 4 years, fiber wall had a dominant thickening every year. Afterwards, the degree of thickening would decrease gradually. The thickening regularity of secondary wall demonstrated that the optimal stage of cutting for cultivating Moso should be about 5 years. At the meantime, the multilamellate structure of fiber in alternate arrangement of narrow and broad lamellae formed gradually, which could attribute to the regular change of climate in a year during secondary wall formation like the growth ring of dicotyledonous woody plants. 2. The organelles as mitochondria, endoplasmic reticulums and Golgi bodies, and other substructures like transfer vesicles, plasmalemma and lomasome, and the cytoskeletal systems, were together involved in fiber primary wall formation. During the process, ATPase localized on fiber plasmalemma played function in the regulation of acid growth, which could provide the preconditions for primary wall formation. For a second messenger of environmental stimuli, Ca2+ could influence fiber nucleus and facilitated the synthesis of RNAs and proteins about primary wall formation, which can upregulate the formation of fiber primary wall. Also, the acid phosphatase (AcPase) distributed on the plasmalemma and transfer vesicles and nucleus of fiber could participate in the synthesis and transportation and exocytosis via vesicles of new cell wall materials. In addition, the Ca2+-ATPase present on the plasmalemma and endomembrane systems like tonoplast could play roles in the maintenance of Ca²⁺ homeostesis, guaranteeing the normal physiological metabolism during fiber primary wall formation. 3. At the early stage of fiber secondary wall formation, the chromatin agglutination, organelle swelling and the tonoplast disintegration and the appearance of multivesicular bodies were all observed. Dense ATPase was also distributed on the agglutinated chromatin and cleavage tonoplast and disintegrated cytoplasm and organelles. TUNEL reaction signals could be detected on these ultrastructures of fiber. Ultrastructural observation, ultracytochemical localization and TUNEL detection all evidenced that fiber secondary wall formation was an active PCD controlled by fiber nuclear genes. The increase of Ca2+ level in cytoplasm and nucleus, and condense concentration of AcPase on the nuclear chromatin and tonoplast, could respectively be one of the reasons bringing fiber PCD. Ca2+ and AcPase were both involved in the breakdown of fiber protoplast during PCD. Furthermore, Ca2+-ATPase could play functions in regulating fiber PCD. 4. At the early stage of fiber secondary wall formation, the secondary wall materials were accumulated in the same manner as the formation of fiber primary wall, and ATPase, AcPase and Ca2+ and Ca2+-ATPase also played vital roles in the process. With the occurrence of fiber PCD, fiber wall would thicken gradually, and the mechanism of fiber secondary wall formation would differ from the former: the production of PCD would be transported via vesicles to build its secondary wall, and the ATPase and AcPase and Ca2+-ATPase persisted on the plasmalemma and plasmalemma invagination and transfer vesicles had important roles in the transportation and exocytosis of new cell wall materials including the production of PCD. With the continual thickening of secondary wall formation, transfer vesicles and plasmodesmata between fiber and its adjacent cells with higher activity of several enzymes as ATPase and AcPase and Ca2+-ATPase were persistent for many years, which contributed to intercellular transportation of nutrients and all kinds of proteins synthesized by its neighboring cells. Ca2+ played important roles in the maintaining normal physiological metabolism during fiber secondary wall formation. 5. During fiber secondary wall formation, the plasmalemma, plasmodesmata and transfer vesicles and the agglutinated chromatin with several enzymes such as AcPase and all kinds of ATPase persisted for many years, which suggested that Moso fiber could keep vigorous metabolism of substances and energy for a long time after PCD, indicating the long-lived characteristic of Moso fiber differed from that of other dicotyledonous woody plants.