Linking the structure of vascular bundles and mineral element deposition reveals the hub role of nodes in bamboo

Nodes are a distinct feature of bamboo plants, categorized into three main types: culm, shoot, and rhizome nodes. However, the latter two are often overlooked due to their underground growth, resulting in a limited understanding of their structure and function. In this study, we examined the structure and mineral elements deposition in the nodes of Moso bamboo (Phyllostachys edulis). Our findings indicate that all three node types possess a complex yet well-organized vascular bundle system, with notable differences. Culm nodes feature enlarged vascular bundles with distinct xylem and phloem regions, whereas shoot and rhizome nodes have less-developed phloem regions. The rhizome node contains a vascular structure of crown root and coronary shoot bud, which is absent in culm and shoot nodes. In culm node, iron accumulation decreases gradually from the bottom to the top, primarily localizing in cells near the enlarged and small vascular bundles. Zinc is deposited in both the enlarged and small vascular bundles in the lower part of the node. In contrast, calcium accumulates predominantly in the upper part, particularly in cells adjacent to enlarged and small vascular bundles including diffuse and parenchyma cells. Potassium is distributed throughout most cells but is less abundant in the pith cavity and xylem transfer cells. In shoot and rhizome nodes, iron, zinc, calcium, and potassium exhibit specific regional and cellular deposition patterns. Overall, the vascular structure and mineral element deposition patterns suggest that bamboo nodes function not only as tissue junctions but also as critical hubs for mineral element deposition and distribution.