Measurement of PI4P Levels in Intact Chloroplasts Isolated from Arabidopsis thaliana

Abstract

Phosphatidylinositol 4-phosphate (PI4P), a major species of phosphoinositides, modulates many fundamental cellular processes. We have recently revealed that PI4P plays an important role in chloroplast division as a negative regulator. Despite its importance in chloroplasts, the content of PI4P in chloroplasts is very low and it is difficult to measure PI4P levels. In this protocol, we describe a simple method that we have developed for measurement of low level of PI4P in chloroplasts. Intact chloroplasts were isolated by a basic method using Percoll gradient centrifugation and acidic lipids were extracted from the isolated chloroplasts. The extracted acidic lipids including PI4P were spotted onto the membrane strip, which had been pre-spotted with PI4P standards and other phosphoinositides as negative controls. PI4P in the spot of acidic lipids on the membrane was detected using a PI4P binding protein.