Pattern of callose deposition during the course of meiotic diplospory in Chondrilla juncea (Asteraceae, Cichorioideae)

Krystyna Musiał,Maria Kościńska-Pająk

doi:10.1007/s00709-016-1039-y

Abstract

Total absence of callose in the ovules of diplosporous species has been previously suggested. This paper is the first description of callose events in the ovules of Chondrilla juncea, which exhibits meiotic diplospory of the Taraxacum type. We found the presence of callose in the megasporocyte wall and stated that the pattern of callose deposition is dynamically changing during megasporogenesis. At the premeiotic stage, no callose was observed in the ovules. Callose appeared at the micropylar pole of the cell entering prophase of the first meioticdivision restitution but did not surround the megasporocyte. After the formation of a restitution nucleus, a conspicuous callose micropylar cap and dispersed deposits of callose were detected in the megasporocyte wall. During the formation of a diplodyad, the micropylar callose cap decreased and the walls of a newly formed megaspores showed scattered distribution of callose. Within the older diplodyad, callose was mainly accumulated in the wall between megaspores, as well as in the wall of the micropylar cell; however, a dotted fluorescence of callose was also visible in the wall of the chalazal megaspore. Gradual degradation of callose in the wall of the chalazal cell and intense callose accumulation in the wall of the micropylar cell were related to the selection of the functional megaspore. Thus, our findings may suggest that callose fulfills a similar role both during megasporogenesis in sexual angiosperms and in the course of meiotic diplospory in apomicts and seems to form a regulatory interface between reproductive and somatic cells.

Highlights

Callose, a β-1,3-linked homopolymer of glucose containing some β-1,6 branches, may be considered as a histological marker for a preliminary identification of the reproduction mode in angiosperms
C. juncea is the second apomictic species in which we described the pattern of callose accumulation in the wall of a cell undergoing meiotic diplospory
We documented the details of callose deposition in the walls of megaspore mother cell (MMC) and during the functional megaspore (FM) selection in the ovules of a diplosporous dandelion T. atricapillum (Musiał et al 2015)

Summary

Introduction

A β-1,3-linked homopolymer of glucose containing some β-1,6 branches, may be considered as a histological marker for a preliminary identification of the reproduction mode in angiosperms. In the majority of sexually reproducing flowering plants, the isolation of the spore mother cell and the tetrad by callose walls is a striking feature of both micro- and megasporogenesis (Rodkiewicz 1970; Bhandari 1984; Bouman 1984; Lersten 2004). Callose functions as a marker to distinguish the reproductive cells from other ovule tissue in plants with mono- and bisporic patterns of megasporogenesis (Rodkiewicz 1970; Russell 1979; Tucker and Koltunow 2014). The pattern of callose deposition is altered in the ovules of apomicts (Drews and Koltunow 2011; Galla et al 2011; Musiał et al 2015). Total absence of callose or an incomplete callose wall in the megasporocyte was essentially

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