Clustering of peroxisomes at the point of contact. Peroxisomes visualized in the cortical cytoplasm underlying the outer epidermal cell wall in a cotyledon of A. thaliana expressing PTS-GFP . The surface of the epidermal cell was touched with a tungsten microneedle at time 0:00. The position of the needle is indicated by the white V-shaped lines at the top of the image. Images A-DD are projections of three optical sections taken at the times indicated in minutes and seconds. The peroxisome labeled "1" becomes immobilized about 10 μm to the left of the needle tip 1 minute after touching the cotyledon surface. About 3 minutes later, this peroxisome moves to the very tip of the needle. Other peroxisomes accumulate in the vicinity of the needle tip before becoming clustered there after about 7 minutes. A movie showing peroxisome aggregation in this experiment is shown in Additional File 10. Bar = 10 μm.