Time course analysis of callose plug formation in the C24 ecotype. (A). Schematic indicating pollen tubes with different callose plug patterns, e.g. the three pollen tubes shown at 4 hours pollen germination represent pollen tubes with a callose plug close to the pollen grain (left), with a callose plug far away from the pollen grain (middle) and one without a callose plug (right). The percentage represents the proportion of pollen tubes with each pattern. Tube lengths in the schematic represent the average pollen tube lengths in Table 1 but are not precisely to scale. (B) A forming callose plug near the pollen tube tip (arrow), sperm cells are behind it (arrowhead). Grain is to the left. (C) Sperm cells (arrowhead) passing through an incomplete callose plug (arrow). Grain is to the left. (D) A completely formed callose plug (arrow), sperm cells are in front (arrowhead). Grain is to the left. Bars = 30μm.