Modulation of ROP1 activity affects vesicle accumulation to the tip. (A) A time series of YFP-RabA4d staining in tobacco pollen tube overexpressing ROP1. Confocal images obtained were focused in the median plane. The numbers beneath each image indicate the time elapsed from the first image. A lower amount of ROP1 plasmid (0.1 μg) was used to weakly express ROP1. A low level of wild-type ROP1 expression induced rapid elongation of pollen tubes. Shown are single laser sections focused on the midplane. (B) Quantitative analysis of A. The mean intensity of YFP-RabA4d accumulated at the tip region and growth rate were determined from each time-lapse confocal image. YFP signal intensity and growth rate were measured every 10 s and plotted as a function of the time. Note that the period of oscillation was reduced to 37.1 ± 7.6 s (n = 6). (C) Representative images of YFP-RabA4d alone (a) or together with DN-rop1 (b) or CA-rop1 (c). DN-rop1 inhibited accumulation of YFP-RabA4d to the tip, whereas CA-rop1 induced tip-focused YFP-RabA4d accumulation. Shown are single laser sections focused on the midplane. Bars, 10 μm. (D) Quantification of YFP-RabA4d accumulation in representative wild-type (control), DN-rop1 OX, and CA-rop1 OX pollen tubes. Pixel intensity values along a central transect (indicated by the box) through each image was measured (left). Similar results were obtained from ∼20 individual pollen tubes.