Spatial and temporal organization of actin during hydration, activation, and germination of pollen inPyrus communis L.: a population study

Summary

Dynamics of F-actin organization during activation and germination ofPyrus communis (pear) pollen was examined using rhodaminephalloidin. Prior to activation, the rhodamine-phalloidin labelling pattern appeared as circular profiles in the peripheral cytoplasm of the vegetative cell and as coarse granules around the vegetative nucleus. In activated pollen, parallel arrays of cortical F-actin were aligned circumferentially, along the polar axis in non-apertural areas of the pollen grain, and at 45° to 90° to the polar axis beneath the apertures. Some pollen also showed fluorescent granules or fusiform bodies dispersed throughout the cytoplasm, but as the number of such pollen diminished with prolonged incubation, these are being considered as intermediate patterns. In later stages, the filaments became organized as interapertural bundles traversing the three apertures. However, prior to emergence of the pollen tube, labelling became confined to a single aperture. In germinated pollen grains, actin microfilaments are aligned more or less axially with respect to the axis of the developing pollen tube.

The granular labelling pattern seen around the vegetative nucleus prior to pollen activation also became clearly filamentous with pollen activation; this filamentous pattern persisted until germination when it was replaced by cables that aligned longitudinally with respect to the emerging tube axis.

The results demonstrate that the organization of actin undergoes considerable changes in the period preceding pollen germination and that microfilament polarization is achieved before pollen germination.