Phosphorus (P), in the form of phosphate ion (Pi), is a vital element contributing in biomolecule structures, metabolic reactions, signaling pathways and energy transfer within the living cells. The objective of the present study was to assess the influence of fungal infection on Pi metabolism in compare to the effects of phosphate stress in Arabidopsis. Quantification of total P contents showed higher storage of P in the shoots than in the roots of Pi-fed plants, while the homeostatic levels of soluble Pi was kept in a fairly narrow range in roots and shoots of both Pi-fed and Pi-starved. When the plants were subjected to Pi starvation, both total P and soluble Pi contents were reduced to minimal levels in roots and shoots. Total acid phosphatase (APase) activity was also affected by the level of available Pi such that it was higher in the starved plants than in the fed plants. When Pi-fed plants were subjected to fungal infections, a remarkable reduction was observed for the above indicators in roots but not shoots. Surprisingly, the analysis of APase expression profiling after inoculation with Alternaria brassicicola showed that the rates of transcription of several APase-encoding genes were affected by fungus infection. Atpap9, afungal inducible gene, promoter analysis also indicated alterations in tissue-specific expression patterns upon the fungal infections. These data clearly illustrate that how a nutrient distribution is affected by environmental conditions, even regardless of available phosphate.