[Investigations on the distribution and transport of ions in plant tissues with the X-Ray microanalyzer : I. Experiments on Vegetative Organs of Zea Mays]

Abstract

1. The distribution of K, Ca, Sr and P in the vegetative organs of Zea Mays was examined. 2. The ions were detected localized in cryostat sections with the X-ray microanalyzer. 3. In meristems (root tip, intercalary meristem in internodes) P is distributed rather uniformly, and K is mainly accumulated in tissues which are about to undergo or are undergoing differentiation. The content of Ca and Sr in meristematic cells is low. 4. Root hairs accumulate ions intensively. 5. The vascular bundle of the root and the big bundles in the sheath and midrib of the oldest leaves show a high ion content. 6. In the vascular bundles, the ions are mainly localized in sclerenchyma and xylem. The phloem always contains much P and in part it also contains a considerable amount of K. 7. The ions are mainly localized to the cell walls in differentiated cells. Cations are partly adsorbed to cell walls or may be bound chemically. Part of the Ca and Sr deposited in cell walls is found as phosphate. 8. A barrier to lateral transport of ions across the root is located in the plasmalemma of the outermost cortex layer. After the transfer across the barrier, ions move in the symplams to the vascular tissue. 9. Translocation of K and P in the root is basipetal in xylem and acropetal in phloem; translocation of Ca and Sr is mainly basipetal. 10. The ions are accumulated in the oldest leaves. P and K may be retranslocated from these leaves in the phloem and later on redistributed to younger leaves. 11. The deposition of ions in the epidermis and bundlesheaths of the shoot is interpreted as salt exeretion.