FIGURE 4.

Arrest of cytoplasmic streaming does not occur simultaneously in all parts of the cell. (A) Treatment with incompatible S-protein. Time periods elapsed between SI challenge and complete arrest of cytoplasmic streaming in the apical and subapical versus the further distal areas are marked and connected for individual pollen tubes. The slopes indicate a spatial gradient. (B) Treatment with actin depolymerizing drugs. The graph shows the time periods elapsed between addition of cytochalasin D (solid circles) or latrunculin A (open circles) and complete arrest of cytoplasmic streaming in the apical and subapical versus the further distal areas of individual pollen tubes. The absence of significant slopes indicates that cytoplasmic streaming is affected simultaneously in all parts of one individual pollen tube.