Effect of Phosphorus Nutrition on the Cellular Distribution of Acid Phosphatase in the Leaves of Lycopersicon esculentum L.

Abstract

A histochemical study using light microscopy has been made of the distribution of acid phosphatase (EC 3.1.3.2) activity in transverse sections of fully expanded leaves of Lycopersicon esculentum grown in phosphate-deficient or sufficient media. Leaf tissues were prepared by two methods and were embedded in paraffin wax. The location of acid phosphatase activity in leaf sections was determined by trapping orthophosphate released from p-nitrophenyl phosphate with lead acetate and subsequently converting the lead phosphate to optically dense lead sulphide. In leaf sections from control tissue lead sulphide deposits were larpely confined to the spongy mesophyll cells. Whereas the staining of the palisade cells was limited and of a granular nature, the staining of the spongy mesophyll cells was heavier and coincident with the outline of the individual cells. Moreover, the minor veins were more heavily stained than the surrounding mesophyll cells. Sections of phosphorus-deficient tissues were heavily stained in both the palisade and spongy mesophyll layers and heavy deposits of lead sulphide were present in the regions of the minor veins. It is suggested that the enhanced acid phosphatase activity of the mesophyll cells in fully expanded leaves could be involved in the remobilization of phosphate within phosphorus-deficient plants, or be part of a phosphate transporting system, concentrating the intracellular phosphate from the limiting supply in the solution bathing the mesophyll cells.