Fig. 2.

Cell membrane-located PRK regulates pollen tube tip growth. LAT52-GFP-Nt-PRK-transformed tobacco pollen tubes are shown. (A) Cell surface localization of GFP-Nt-PRK in elongating pollen tubes. Typical of pollen tube cell membrane-associated proteins, vesicles loaded with FP-PRKs also concentrate in and cycle rapidly in and out of the apical cytoplasm (see also Cheung et al. 2002), which is known to be occupied almost exclusively by transport vesicles. (B–D) Prevalent tip growth defects induced by expression of GFP-Nt-PRK. (B) Balloon tipped and growth arrested. (C) Bifurcated tip; the vacuole-occupied branch (lower, DIC image) was either already growth arrested or likely to cease growth shortly after the image was acquired. (D) A bifurcated GFP-Nt-GFP-expressing pollen tube where growth at both tips had been sustained for some time. Balloon-tipped but not bifurcated tubes were observed previously in LePRK2-transformed pollen tubes (Zhang et al. 2008).