Tissue accumulation patterns and concentrations of potassium, phosphorus, and carboxyfluorescein translocated from pine seed to the root.

MAIN CONCLUSION: Potassium (K), phosphorous (P), and carboxyfluorescein (CF) accumulate in functionally distinct tissues within the pine seedling root cortex. Seedlings of Pinus pinea translocate exogenous CF and endogenous K and P from the female gametophyte/cotyledons to the growing radicle. Following unloading in the root tip, these materials accumulate in characteristic spatial patterns. Transverse sections of root tips show high levels of P in a circular ring of several layers of inner cortical cells. K and CF are minimal in the high P tissue. In contrast, high levels of K and CF accumulate in outer cortical cells, and in the vascular cylinder. These patterns are a property of living tissue because they change after freeze-thaw treatment, which kills the cells and results in uniform distribution of K and P. K concentration can be reduced to undetectable levels by incubation of roots in 100 mM NaCl. Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis and scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS) of root segments both reliably determine K and P concentrations.