Dear Editor,Plasma membrane (PM)-Iocalized PIN-FORMED (PIN)auxin efflux carriers were shown to cycle rapidly and continuously between PM and the endomembrane system and this cycling is affected by many exogenous factors and endogenous programs (Grunewald and Friml,2010).The fungal lactone metabolite Brefeldin A (BFA) is believed to interrupt the continuous cycling of PINs and other PM proteins by inhibiting their re-secretion (Kleine-Vehn and Friml,2008).Proteins are congregated in a large vesicular structure called BFA compartments (BFACs;Robinson et al.,2008).In many studies,the failure to detect PIN-labeled BFACs was considered a sufficient sign of PINs endocytosis inhibition (Paciorek et al.,2005;Dhonukshe et al.,2007;Robert et al.,2010).However,the activity of BFA on plant cells seems to be more complex.The results obtained using different organelle markers imply that distinct populations of aggregates induced by BFA application might exist and that clustering of different subcellular structures depends on the concentration and duration of BFA exposure (Robinson et al.,2008;Lam et al.,2009a,2009b).