Interference of intracellular inorganic phosphate analysis by phosphatase in Papaver somniferum cell suspensions

The analysis of intracellular inorganic phosphate in aqueous homogenates of Papaver somniferum cell suspensions results in an overestimation of intracellular inorganic phosphate (P_i) levels by as much as 300% due to protein interference and apparent phosphatase activity. Precipitation of protein with zinc sulfate results in a better estimate of intracellular P_i; however, phosphatase activity is still significant. Trichloroacetic acid (TCA) extraction effectively precipitates protein and eliminates phosphatase activity. Neutralization of the TCA extract prevents residual acid interference with subsequent colorimetric inorganic phosphate analysis. TCA extraction is shown to be a superior method for the analysis of intracellular P_i, especially in phosphate‐depleted plant cells.