Histological Compartmentation of Phosphate in Vicia faba L. Leaflet

Guard cells, epidermal cells, palisade parenchyma cells, and spongy parenchyma cells of Vicia faba L. leaflet were analyzed for inorganic phosphate and phosphorus. On a molar basis, cells in the epidermal layer contained about 15-fold more inorganic phosphate than mesophyll cells did. Although a metabolic role for this asymmetric distribution cannot be defined unequivocally, we note that high epidermal inorganic phosphate would buffer against pH changes in the epidermis during stomatal movements.