Abstract
Phosphorus contents of epidermal vacuoles and mesophyll cells of Lupinus lutens leaflets were measured by electron probe x-ray microanalysis of fully hydrated, bulk frozen samples. Quantitation was achieved using standard solutions containing colloidal graphite to simulate cell contents and the derived nonlinear relationship between peak over background ratio and concentration improved the accuracy of the analytical procedure. Inorganic phosphate contents of mesophyll cells were shown to be highly dependent on phosphate nutrition. Comparison with data obtained from conventional analysis leads to the suggestion that in heterogeneous tissues the inorganic phosphate concentrations of the cytoplasm may show greater variation than observed in the cytoplasm of simple plant systems such as cell suspension and root tips.