Abstract
Although callose occurs during megasporogenesis in most flowering plants, the knowledge about its general function and the mechanisms by which the callose layer is formed in particular places is still not sufficient. The results of previous studies suggest a total lack of callose in the ovules of diplosporous plants in which meiosis is omitted or disturbed. This report is the first documentation of callose events in dandelions ovules. We demonstrated the pattern of callose deposition during the formation of megaspores through diplospory of Taraxacum type and during normal meiotic megasporogenesis in apomictic triploid Taraxacum atricapillum and amphimictic diploid Taraxacum linearisquameum. We found the presence of callose in the megasporocyte wall of both diplosporous and sexual dandelions. However, in a diplosporous dandelion, callose predominated at the micropylar pole of megaspore mother cell (MMC) which may be correlated with abnormal asynaptic meiosis and may indicate diplospory of the Taraxacum type. After meiotic division, callose is mainly deposited in the walls between megaspores in tetrads and in diplodyads. In subsequent stages, callose gradually disappears around the chalazal functional megaspore. However, some variations in the pattern of callose deposition within tetrad may reflect variable positioning of the functional megaspore (FM) observed in the ovules of T. linearisquameum.
Highlights
Callose (β-1,3-glucan polymer) plays a significant role during reproductive processes occurring in the anthers and ovules of flowering plants
It has been proposed that callose functions as a molecular filter between the genetically different cells, decreasing the permeability of the cell wall, and it serves as a selective barrier which transmits only specific signals that are essential to meiosis (Heslop-Harrison and Mackenzie 1967; Rodkiewicz 1970; Bhandari 1984; Bouman 1984)
The deposition of callose in the megaspore mother cell (MMC) wall is a specific feature of angiosperms with the monosporic and bisporic type of female gametophyte development, whereas callose is absent in species with the tetrasporic type of megagametophyte formation (Rodkiewicz 1970)
Summary
Callose (β-1,3-glucan polymer) plays a significant role during reproductive processes occurring in the anthers and ovules of flowering plants. The deposition of callose in the megaspore mother cell (MMC) wall is a specific feature of angiosperms with the monosporic and bisporic type of female gametophyte development, whereas callose is absent in species with the tetrasporic type of megagametophyte formation (Rodkiewicz 1970). A reduction or complete absence of callose in MMC walls was suggested in apomicts exhibiting meiotic diplospory of Taraxacum and Ixeris types (Carman et al 1991; Peel et al 1997) In these types of diplospory, unreduced megagametophytes are formed from megaspores that are a result of a restitutional meiosis, i.e., a modified megasporogenesis without the first reduction division (Gustafsson 1946; Nogler 1984; Asker and Jerling 1992)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
