| Bamboo plants are an important part of terrestrial forest ecosystem,mainly composed of parenchyma cells,fibers and vessel elements.Parenchyma cells,which account for more than52%of the total amount of bamboo tissue,are sponge tissue and buffer tissue,which have storage,transmission,photosynthesis and all kinds of metabolism during growth,and play an important role in the excellent physical and mechanical properties of bamboo.The cell wall is also an important component structure of parenchyma cells,and its structure,composition and state are closely related to cell growth and development,physiological function and mechanical properties.The pits is also an important structure of the cell wall,which is the main transport passage of water,nutrients and other substances between cells.The further study on the ultrastructure of bamboo parenchyma cells not only plays an important role in understanding growth,physiological function,mechanical properties and structural characteristics,but also plays an important role in the theoretical gap of the anatomical structure of bamboo parenchyma cells.It also has important guiding significance for the construction of model of moisture absorption and desorption,the exploration of excellent flexibility of bamboo,the high value-added utilization of parenchyma and the design of biomimetic materials.The ground and vascular parenchyma cells in the minddle part of the tenth section of the four-year ages moso bamboo(Phyllostachys edulis)culm were studied.The cell morphology,cell wall structure and pit structure of bamboo parenchyma cells were studied by optical microscope(LM),field emission scanning electron microscope(EF-ESEM),transmission electron microscope(TEM),laser confocal fiber microscope(CLSM)and the resin casting technology.Additionally,Image J and Origin software are also used to process and analyze images and data.The three-dimensional structure of cells was constructed by combining the structural morphology,structural parameters and three-dimensional composition software.The following key results were drawn:(1)The morphological diversity and quantitative characteristics of parenchyma cells.The ground parenchyma cells were mainly divided into long cells and short cells.The cell wall was only the primary cell wall thickening and the secondary wall thickening.The pits included simple pits and primary pit-field.The vascular parenchyma could be divided into cells with two transverse end walls(TT-type cell),cells with one oblique end and one transverse end walls(OT-type cell),and cells with two oblique end walls(TO-type cell).Additionally,there were two types of thickening patterns of the secondary wall,uniform and reticulate thickening,and both diffuse pitting and opposite-alternate pitting were observed.The average values of length,width,lumen diameter,double wall thickness,area and number of long(short)cells were 125.75(24.57)?m,53.44(44.93)?m,43.76(38.33)?m,9.67(6.56)?m,1360.92cm~2 and533000(58524.78)cells/cm~2,respectively.That of the vascular parenchyma cells were 139.0?m,17.3?m,10.4?m,6.9?m,and 51.1?m~2,692382 cells/cm~2,respectively.Besides being filled with long cells,starch was found in a small amount in short cells,and the starch granules were various in morphology,and 2?5 starch granules formed starch groups.(2)The multi-wall layers structure and quantitative characteristics of parenchyma cell walls.The secondary wall sub-layers of parenchyma cells was usually an odd layers,and were exhibited tight-loosely(light-dark)alternating layers.Most parenchyma cells were observed to have 7 sub-layers,with a maximum of 11 sub-layers of ground parenchyma cells and 9sub-layers of vascular parenchyma cells in 4-year ages moso bamboo.The average thickness of each cell wall sub-layer in ground parenchyma cells(0.32-0.41?m)was thicker than that in vascular parenchyma cells(0.26-0.32?m).Additionally,the microfibril angle of adjacent sub-layers was opposite,but the microfibril arrangement of adjacent lateral wall was the same.The average MFA of the secondary wall of the parenchyma cells of the basic tissue was60°(-65°),while that of the vascular bundle parenchyma cells was 54°(-52°).(3)Morphological and quantitative characteristics of parenchyma cell pits.The type pit of Parenchyma cells included simple pit(main)and bordered pit(occasional),and some primary pit-field.The pit aperture had different morphology,including elliptical,circular or lenticular aperture,with protoplasts or granular material.The pit cavity was divided into cylinder-like and branched cavity.Parenchyma cells existed normal pit membrane and primary pit-field pit membrane,which is generally heterogeneous and often contained crustal material.Addtionally,the pit membrane of ground parenchyma cells existed numerous pores,and that of vascular parenchyma cells had some plasmodesmata.The average values of pit area,length of long and shot axis,length of pit canal,diameter and thickness of pit membrane in the ground parenchyma cells were 0.57?m~2?1.16?m?0.66?m?4.34?m?1.67?m?0.54?m,that in the vascular parenchyma cells were 1.56?m~2?1.73?m?1.19?m?2.56?m?2.25?m?0.36?m.Meanwhile,the number of pits of long and short cell was 0.026 pits/?m~2 and 0.062 pits/?m~2.(4)Morphological and quantitative characteristics of parenchyma cell ramiform pits.The ramiform pits have a diverse morphology that can be divided into main categories:type I(the primary branches)and type II(the secondary branches).The distribution of ramiform pits is different in ground parenchyma cells and vascular parenchyma cells.The number of ramiform pits in GPCs and VPCs was 1.5 pits/cell wall and 4?6 pits/cell wall.The average values of pit area,length of long and shot axis,length of pit canal of large simple pit and two branched pits of ramiform pits in the GPCs were(1.9?m~2,2.5?m,1.0?m,2.5?m),(0.3?m~2,0.9?m,0.5?m,1.9?m),(0.4?m~2,1.0?m,0.6?m,2.0?m).That in the VPCs were(4.4?m~2,3.0?m,1.9?m,1.8?m),(1.0?m~2,1.5?m,0.9?m,1.4?m),(1.5?m~2,1.7?m,1.1?m,1.6?m).The angle between two branched pits of GPCs was 32.0°,and that of VPCs was 29.5°.(5)Through the analysis of cell morphology,cell wall structure parameters and pit structure parameters,the differences micro-structures and functions of ground and vascular parenchyma cells were compared and studied,and the three-dimensional structure of ground parenchyma cells was reconstructed,and the cell wall model of bamboo was innovated. |
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