The apoplast can be described as the soluble fraction of the extracellular space of plant tissue, and it plays an important role in signaling, nutrient transport, and plant-pathogen interactions. In this protocol, we describe a method where leaves are infiltrated with phosphate buffer under vacuum. The apoplast can then be extracted by centrifugation and simultaneously collected in a protease inhibitor solution. Using this protocol, typically 3 μg of apoplastic proteins can be obtained in a volume of 300 μL from five potato leaflets, with minimal contamination by non-apoplastic proteins.
Keywords: Apoplast; Apoplastic protein; Extracellular space; Phosphate buffer; Protease inhibitor; Secretome; Soluble fraction; Vacuum infiltration.