Ultrastructural Studies of Gametophytic Apomicts in Guinea Grass (Panicum maximum) I. Differentiation of Aposporous Initial Cell

Abstract

SummaryThe ultrastructural features of the developing megasporocyte, especially the timing of degeneration of sexual cells during megosporogenesis, and differentiation of aposporous initial cell (AIC) in facultative apomictic guinea grass (Panicum maximum) has been studied. The first degeneration was observed in dyad stage. Accompanying the degeneration of sexual cell, the cell adjacent to the dyad in chalazal side, derived from nucellus began to increase its size of cell and change its organelles and shape, and thus, the cell become to the first AIC usually located in micropylar side. The AIC appeared in order continently adjacent to the first AIC in the chalazal side. However, all of the AICs could become to the mature embryo sac with 4-nucleates. The interdependent patterns of the nucellar cell and AIC, and their relationship are also discussed at subcellular level.

Ultrastructural Mechanisms of Aposporous Embryo Sac Initial Cell Appearance and Its Developmental Process in Gametophytic Apomicts of Guinea Grass (Panicum maximum)

“…However, it is considered that nucellar cells located in chalazal end inherit and develop dominantly when they sense some signals from sexual ones which will be the fate of abortion and degeneration, and/or lose capacity of division. At the same time, one of nucellar cell-derived AIC cells appears, sexual cells and other nucellar cells provide nutrients for AIC differentiation (Guan et al 2006(Guan et al , 2007(Guan et al , 2008. In some meanings, the life of the ovule (or ovary) will be kept by whatever either sexual or asexual (nucellar) cell becomes to embryo sac.…”

“…However, ultrastructural data about apospory and other types of apomixis are scarce and not discussed in recent publication (Koltunow 1993). And thereafter, ultrastructural analysis of AIC appearance in P. maximum have been reported in KK-15 by Naumova and Willemse (1995), and in two varieties of 'Petrie' and 'Gatton' by Chen and Guan (2006), respectively. This study shows ultrastructural characteristics of the reproductive cells in AIC-derived embryo sac.…”

Establishment of Efficient System for Isolation and Manipulation of Single Protoplasts Containing Aposporous Embryo Sac Initial Cell in Guinea Grass (Panicum maximum)

“…The authors have reported that the most different event between the sexual and apomictic plants was the appearing of aposporous embryo sac initial cell (AIC) following the degeneration of the mature haploid megaspore in guineagrass (Panicum maximum). This was observed by Normarski differential interference-contrast microscopy (DIC), and transmission electron microscopy (TEM) [5][6][7][8]. And according to the above results, the authors have obtained the apomixis-specific gene, named as ASG-1, from facultative apomict of guineagrass, using the differential screening method based on the ovary length as an index [9,10].…”