AP activity (solid lines) and sll0654 gene expression (dashed lines). (A) WT Synechocystis following transfer from Pi-replete to Pi stress conditions. □, Pi-replete conditions; ⧫, Pi stress conditions. (B) sphX, pstS1, and pstS2 disruption mutants following transfer from Pi-replete to Pi stress conditions. Squares, pstS1 mutant; diamonds, pstS2 mutant; triangles, sphX mutant. All AP assays were performed in triplicate. Error bars indicate maximum standard deviations observed.