The Cytological Mechanisms Of The Ground Tissue Cell Wall Formation During The Elongation Growth In Phyllostachys Edulis ’Pachyloen’ Culms

In this paper,Phyllostachys edulis ‘Pachyloen’ was studied closely around the theme of the interrelationship between internode elongation and ground tissue cell walls during the rapid elongation growth.The dynamic changes of ground tissue cell walls were investigated with a series of testing techniques and methods,such as: light microscopy,electron microscopy(TEM),field emission scanning electron microscopy(FEG-SEM)and fluorescence microscopy.The cytological mechanisms of the construction of ground tissue cell walls during the rapid elongation growth in Phyllostachys edulis ‘Pachyloen’ culms were elucidated.According to the light microscopy observation,the development of ground tissue was divided into primary wall formation stage and secondary wall formation stage.Cells had no significantly elongation and remained active cell division at the early stage of primary wall formation.the cell walls of the ground tissue thickened but not significant,and a large number of thin new walls could observed under the electron microscope.the orientation of the microfibrils was perpendicular to the cell axis.smaller intercellular space,more plasmodesmata,rich organelles.In the abnormal nodes,the mitochondria degraded.The cells contained a large amount of starch grains.Some cells began elongation,but a small number of cells had no elongation and developed into short cells at the late stage of primary wall formation.With the differentiation and development of the ground tissue,the cell walls gradually thickened,the arrangement direction of the microfibrils interweaved network and loose.TEM results showed that the orientation of the primary wall microfibrils was parallel to the cell axis.At the late stage of primary wall formation,the intercellular space becomes larger,and part of them contained degradants.The plasmodesmata in normal nodes were richer than in abnormal node and the electron density of the cytoplasm was greater.The lack of septa(abnormal node)had no obvious effect on the differentiation of long and short cells by the light microscope.There were more starch grains in abnormal nodes than that in normal ground tissue cells.During the secondary wall development,the differentiation of long and short cells was obvious.In the formation of the secondary wall,the long cell walls thickened,and the microfilaments of the secondary wall spirally oriented with different orientation angles.With the gradually thickening of the secondary wall,the long cells of the ground tissue formed a multi-layered structure,and it can be observed that the two wall microfilaments adjacent to the cell wall arranged at a certain angle,in which the microfibrils of a certain raw layer.The arrangement of the microfibrils in one of the secondary walls was parallel to the cell axis or at a small angle.Long cell contents mostly degraded.The distribution of a few starch grains can still observed in some ground tissue cells.During this period,two anomalies found in the abnormal nodes: A white substance with low electron density in the intercellular layer and white protruding material with low electron density on the cell walls of ground tissue.By statistical analysis of the length and number of ground tissue cells in different developmental stages,it was found that abnormal nodes caused an increase in the number of cells and a decrease in cell length.The above results indicated that internode elongation was determined by cell division and elongation.The node plays an important role during internode elongation.The rapid growth of bamboo stalks mainly depends on the internode meristem of the nodes.In the section,the complex network system formed by the divergence of vascular bundles is conducive to the lateral transportation of substances.The horizontal transportation of substances is mainly in the nodes.Abnormal nodes lead to the changes of material transport structure,which in turn affect the elongation of the internode,resulting in shorter internodes.In different stages of development of ground tissue,the cell walls gradually thickened,and the arrangement direction of microfibrils changed correspondingly.When the microfibrils arranged perpendicular to the cell axis,it was not conducive to the elongation of the cells,and the microfilaments interweaved in a reticular arrangement helped the cell walls to expand.During the process of cell walls thickening,each layer of the cell walls controls the elongation and growth of cells by constantly changing the direction of microfibrils deposition,thereby regulating internode elongation.