Tobacco pollen and pollen tubes used for comparative transcriptomic analyses. (a) Pollen from stage six of male gametophyte development , representing mature bicellular pollen with fully elongated germ cell (GC) alongside vegetative nucleus (VN), inset. Scale bar = 40 μM. (b) Pollen tubes cultivated in vitro for 4 h still at the bicellular stage. Scale bar = 60 μM. (c) Pollen tubes cultivated in vitro for 10 h with mixed population of premitotic germ cells (red inset) and those with newly formed sperm cells, SC (white inset). Scale bar = 60 μM. (d) Analysis of pollen-tube germination rate and length of pollen grains used in this study that were harvested at different times during the summer period. No significant differences in pollen fitness were observed, irrespective of time of collection.