Visual Detection of Inorganic Orthophosphate in Phloem Cells.

The phloem plays a vital role in actively transporting soluble organic compounds-such as sugars, minerals, and proteins-from source to sink tissues, a process driven by turgor pressure and adenosine triphosphate (ATP)-dependent energy. Since ATP levels in phloem cells are closely linked to inorganic orthophosphate (Pi) availability, precise and efficient detection of Pi in these cells is essential for understanding phloem function. To address this, we developed the inorganic orthophosphate staining assay (IOSA), a method for visually detecting Pi in phloem cells. As a demonstration, we have successfully applied IOSA to the quantification of Pi levels in rice stem phloem cells.