Altered NO3- assimilation in P-stressed plants

To examine P stress effects on NO3- uptake and assimilation, young tobacco plants were deprived of external P for 12 days and at selected times exposed to 15NO3- for 12h uptake periods. In -P plants, tissue P concentrations and growth decreased progressively with time relative to controls. Uptake of 15NO3- per g root DW was restricted markedly, being 70% of the control rate on the day 3 and only 17% on day 9. Additional disruptions in the NO3- assimilation pathway were evident, as larger proportions of absorbed 15NO3- were retained in the root and soluble reduced-15N accumulated in leaves with increasing P stress. The results indicate that transport processes controlling NO3- uptake into the root symplasm and its release into the xylem are major points of regulations in plants responding to P deficiency