Rapid Swelling of Pollen Grains in Response to Floret Opening Unfolds Anther Locules in Rice (Oryza sativa L.)

Abstract

The changes in pollen grain diameter were examined in relation to the floret opening and anther dehiscence in rice (Oryza sativa L.). In the first experiment, the florets were artificially opened by excising the top of the glumes at various times before the expected natural flowering time. Pollen diameter increased rapidly in the artificially opened florets, but slowly in the controls in which the glumes were left intact. The time of anther dehiscence coincided well with the time when pollen grains reached their maximum diameter. In addition, the pollen grain diameter was significantly correlated with the percentage of dehisced anthers in the florets artificially opened at various times. These results indicate that floret opening induces the swelling of pollen grains and that the swelling is an important event for anther dehiscence. In the second experiment, anther segments with pollen left remaining intact and those with pollen removed were immersed in water. The septa in the anther segments without pollen failed to rupture in water, whereas 70% of the septa in the anther segments with pollen left remaining ruptured, indicating that the septa can be ruptured by the swelling pressure of pollen grains resulting in unfolding of anther locules. From these findings, we infer that the rapid swelling of pollen grains in response to floret opening is a driving force to rupture the septum and unfold the locules.