Studies On Developmental Biology Of Phloem Ganglion In Phyllostachys Edulis

The developmental anatomy, cytochemistry and physiological function of phloem ganglion in the node of phyllostachys edulis (Carr.) H. de Lehaie were investigated with light and electron microscopy and cytochemistrial methods. The results are as follows: Under the light microscope, the phloem ganglion, which always locates at the bifurcation of the phloem, changed greatly in cytological characters with its differentiation. Accoding to these changes, the development process of phloem ganglion was divided into three phases: initiating phase, developmental phase and maturation phase. During the differentiation of phloem ganglion, the tonoplast of the cells consisting of the structure broke down at first. And then the cytoplasm begun selective autolysis and the nuclei degenerated. As a result of maturation, the phloem ganglion cell has a thin layer of parietal cytoplasm which consists chiefly of mitochondria, ER and P-protein. The nacreous wall was observed. The plasmodesmata may ramified, and callose layer deposited around the pore of plasmodesmata. Ultrastructure of mature phloem ganglion cell is like with that of normal sieve element, but there are some differences between them. First, the mature phloem ganglion may keep some differentiating cells and archaeocyte. Second, the frequency of plasmodesmata connecting mature phloem ganglion cells is bigger than that of the normal sieve element. Also the diameter of plasmodesma is between that of sieve pore and normal Plasmodesma. So the phloem ganglion cell could be considered as the metamorphosis of sieve element. Cytochemical study on the phloem ganglion showed that: Ca²⁺ transfered from the outer of the cell into the inner with the development of the phloem ganglion, and the changes of Ca²⁺ distribution made the phloem ganglion generate. Ca²⁺ regulated the physiological function of the phloem ganglion. The plasma membrane, plasmodesmata and nuclei always have high Ca²⁺-ATPase activity, which indicated that the phloem ganglion has active symplastic transport and physiological metabolism. Polysaccharide in the phloem ganglion exists always in soluble status, so the phloem ganglion is the main conducting path of substance. The above results suggest that the phloem ganglion is a transfer station, pump and storage structure in substance transport, especially in short distance transport.