Callose is integral to meiotic diplospory of the Taraxacum type: new evidence from ovules of Chondrilla brevirostris (Asteraceae-Cichorioideae)

Abstract

ABSTRACTAn essential, but still not fully understood, aspect of angiosperms’ reproduction is the issue of callose deposition during early female reproductive processes in sexual and apomictic taxa. It was believed that callose may be a marker for an early identification of the reproduction mode and lack of callose was suggested as characteristic for apomicts. However, our findings clearly prove that meiotic diplospory of the Taraxacum type is accompanied by callose deposition and show that lack of callose is not an obligatory feature of the apomictic reproduction mode. In young ovules of C. brevirostris, callose was a marker of the cell entering the first meiotic division restitution. Synthesis and degradation of callose followed a strictly defined pattern, which differed from that described in the majority of analyzed angiosperms. Callose deposition began at the micropylar pole of the diplosporous megaspore mother cell and, finally, this cell wall polysaccharide showed a bipolar location. This pattern dynamically changed in the later stages of meiotic diplospory and, like in sexual species, it was related to the selection of the functional megaspore. Thus, it seems that callose can play a similar regulatory function in cell-cell communication between somatic tissues and the reproductive precursor cell in the ovules of both sexual and diplosporous taxa.