Abstract
The genus Polianthes belongs to the subfamily Agavoideae of the Asparagaceae family formerly known as Agavaceae. The genus is endemic to México and comprises about 15 species, among them is Polianthes tuberosa L. The aim of this work was to study and characterize the embryo sac and early embryo development of this species in order to generate basic knowledge for its use in taxonomy, in vitro fertilization and production of haploid plants and to complement studies already performed in other genera and species belonging to the Agavoideae sub-family. It was found that the normal development of the P. tuberosa var. Simple embryo sac follows a monosporic pattern of the Polygonum type and starts its development from the chalazal megaspore. At maturity, the embryo sac is of a pyriform shape with a chalazal haustorial tube where the antipodals are located, just below the hypostase, which connects the embryo sac with the nucellar tissue of the ovule. The central cell nucleus shows a high polarity, being located at the chalazal extreme of the embryo sac. The position of cells inside the P. tuberosa embryo sac may be useful for in depth studies about the double fertilization. Furthermore, it was possible to make a chronological description of the events that happen from fertilization and early embryo development to the initial development of the endosperm which was classified as of the helobial type.
Highlights
The genus Polianthes belongs to the subfamily Agavoideae of the Asparagaceae family formerly known as Agavaceae (APG III 2009)
Most of the studies on the embryogenesis of Asparagaceae describe the embryo sac development as of the Monosporic–Polygonum type such as in Yucca rupicola (Watkins 1937), Yucca aloifolia (Wolf 1940), Agave lechuguilla (Grove 1941), Agave virginica (Regen 1941), Hesperocallis undulata and Leucocrinum montanum (Cave 1948), Comospermum yedoense (Rudall 1999), Agave tequilana (Escobar-Guzmán et al 2008; González-Gutiérrez et al 2014), Yucca elephantipes (Cruz-Cruz 2013) and Yucca filamentosa (Reed 1903), being the exception Agave fourcroydes and Agave angustifolia (Piven et al 2001) in which the embryo sac was reported as bisporic of the Allium type
Megasporogenesis Megasporogenesis starts with the differentiation of an arquesporial cell that becomes the megaspore mother cell (MMC) which distinguishes from all other cells of the ovule primordia, since it has a larger size than the surrounding cells, its shape is circular to semicircular with an average diameter of 18.69 ± 2.33 μm, its nucleus is dense and well defined (Fig. 1a), and sometimes it is possible to observe the unorganized chromatin in the nucleus by way of filaments (Fig. 1b)
Summary
The genus Polianthes belongs to the subfamily Agavoideae of the Asparagaceae family formerly known as Agavaceae (APG III 2009). The species is commercially propagated by asexual methods which have reduced its Embryological studies comprising the formation of male and female gametes, double fertilization and embryo development and endosperm (Maheshwari 1950) allow the understanding of factors that control the processes of embryonic development in order to manipulate them for practical applications (Bhojwani and Bhatnagar 1983). In this regard, the female gametophyte plays a critical role in every stage of the reproductive process such as the direction of pollen tube growth towards the egg (Higashiyama 2002), the transport of sperm nuclei of the embryo sac through the central and egg cells in the process of double fertilization (Lord and Russell 2002; Russell 1993; González‐Gutiérrez and Rodríguez‐Garay SpringerPlus (2016)5:1804. Reports about female gametophyte development, fertilization and embryo development in the genus Polianthes in the species P. tuberosa are not available
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