The delivery of cell wall material and membrane to growing plant cell surfaces requires the spatial and temporal coordination of secretory vesicle trafficking. Given the small size of vesicles, their dynamics is difficult to quantify. To quantitatively analyze vesicle dynamics in growing pollen tubes labeled with the styryl dye FM1-43, we applied spatiotemporal correlation spectroscopy on time-lapse series obtained with high-speed confocal laser scanning microscopy recordings. The resulting vector maps revealed that vesicles migrate toward the apex in the cell cortex and that they accumulate in an annulus-shaped region adjacent to the extreme tip and then turn back to flow rearward in the center of the tube. Fluorescence recovery after photobleaching confirmed vesicle accumulation in the shoulder of the apex, and it revealed that the extreme apex never recovers full fluorescence intensity. This is consistent with endocytotic activity occurring in this region. Fluorescence recovery after photobleaching analysis also allowed us to measure the turnover rate of the apical vesicle population, which was significantly more rapid than the theoretical rate computed based on requirements for new cell wall material. This may indicate that a significant portion of the vesicles delivered to the apex does not succeed in contacting the plasma membrane for delivery of their contents. Therefore, we propose that more than one passage into the apex may be needed for many vesicles before they fuse to the plasma membrane and deliver their contents.

Ossifying renal tumor of infancy (ORTI) is a rare, benign pediatric tumor of the kidney. Since first reported by Chatten in 1980, 23 cases have been published. Previous authors have argued that ORTI might originate from nephrogenic rests, thereby sharing a pathogenic relationship with Wilms' tumor (WT). ORTI is characterized histologically by a population of polygonal osteoblast-like cells around an osteoid core and densely cellular component of blastemal-like or spindle cells. While the immunohistochemical profile of the cellular components has been reported, to the best of our knowledge, the status of WT1 expression has only been reported once, where it showed negative marking. Mitoses have been described only sporadically in this neoplasm. We report on a case of ORTI with positive WT1 immunohistochemical marking and numerous mitoses. This case highlights a possible pitfall for misdiagnosing ORTI as a WT and provides additional insight into its pathogenesis.