Ultrastructural characterization of the cytoplasmic channel formation between pollen mother cells of David lily

Abstract

The biogenesis and the ultrastructure of cytoplasmic channel were investigated in pollen mother cells of Lilium davidii. It was found that the cytoplasmic channel began to form at leptotene, and extensively ultrastructural observations revealed that its formation was initiated by the local removal of the primary wall and the middle lamella, but leaving plasmalemma intact, yielding a cluster of unopened gaps/channels 110–1100 nm wide. Afterwards at zygotene, the plasmalemma of the two adjacent cells at these sites ruptured, curved toward and fused with each other, finally leading to formation of the cytoplasmic channel. Following later zygotene and with the quickly depositing and thickening of a secondary wall layer, the cytoplasmic channels grew rapidly in their length, and the phenomenon of intercellular movement of chromatin and organelle through these channels (cytomixis) became more and more active. After pachytene stage, the cytoplasmic channels were gradually occluded by callose deposition. Most cytoplasmic channels were observed to be non-branched and lined by plasmalemma, with two broader and symmetrical ends and diameters generally being 200–600 nm, and up to 3500 nm at maximum.Within the cytoplasmic channels, some microfilament- and microtubule-like structures were found extended from one cell to its neighbor in association with the chromatin, or organelles passing through the cytoplasmic channels. This result suggests that the microfilament /microtubule system is involved in the nuclear and cytoplasmic intercellular movement through the cytoplasmic channels. © 2002 Taylor & Francis Group, LLC.