Meiotic restitution mechanisms involved in the formation of 2n pollen in Agave tequilana Weber and Agave angustifolia Haw.

Víctor Manuel Gómez-Rodríguez,Rodrigo Barba-Gonzalez,Benjamín Rodríguez-Garay

doi:10.1186/2193-1801-1-17

Víctor Manuel Gómez-Rodríguez, Rodrigo Barba-Gonzalez + Show 1 more

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https://doi.org/10.1186/2193-1801-1-17

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Journal: SpringerPlus	Publication Date: Sep 13, 2012
Citations: 51	License type: cc-by

Affiliation: Secretaría de Salud de Jalisco

Abstract

A cytological analysis of the microsporogenesis was carried out in the Agave tequilana and A. angustifolia species. Several abnormalities such as chromosomal bridges, lagging chromosomes, micronuclei, monads, dyads and triads were found. The morphological analysis of the pollen, together with the above-mentioned 2n microspores, allowed us to confirm the presence of 2n pollen as well as its frequency. In both A. tequilana and A. angustifolia two different mechanisms were observed: the first mechanism, a failure in the cytokinesis in meiosis II caused the formation of dyads with two 2n cells and triads containing two n cells and one 2n cell; the second mechanism, involves an abnormal spindle, which caused the formation of triads with two n cells and one 2n cell. Likewise, the presence of monads was detected in both species, these, might be caused by a failure of the cytokinesis in both meiotic divisions. This is the first report about the presence of a Second Division Restitution mechanism (SDR) which causes the formation of 2n pollen in the genus Agave. The genetic implications of the presence of 2n pollen in the genus Agave are discussed.

Highlights

In plants, polyploidy represents an important adaptation and specialization mechanism, and it is estimated that more than 70% of all the angiosperms are polyploids (Ramsey and Schemske 1998; Otto 2007); likewise, molecular analyses suggest that most of the existing angiosperms (>90%) show one or several events of duplication of their genomes, of which many species have undergone this phenomenon only recently (Leitch and Leitch 2008)
We describe different abnormalities found in the microsporogenesis of Agave species, including dyads and triads; further, the morphological analysis of pollen allowed us to confirm the presence of 2n pollen
Microsporogenesis analysis and restitution mechanisms In the studied species of the genus Agave, a successive microsporogenesis, characteristic of this genus, was observed, where immediately after telophase I and telophase II a cytokinesis appears, which causes the formation of a dyad, and a tetrad

Summary

Introduction

Polyploidy represents an important adaptation and specialization mechanism, and it is estimated that more than 70% of all the angiosperms are polyploids (Ramsey and Schemske 1998; Otto 2007); likewise, molecular analyses suggest that most of the existing angiosperms (>90%) show one or several events of duplication of their genomes, of which many species have undergone this phenomenon only recently (Leitch and Leitch 2008). One of the possible origins of the polyploid species is through unreduced gametes (2n) (Harlan and De Wet 1975), which occur in most angiosperms (Ramanna and Jacobsen 2003) and have a sporophytic chromosomal number instead of the gametophytic one. It has been mentioned that in the genus Agave some of the species form 2n pollen (López-Díaz S, personal communication), the originating mechanisms have not been elucidated so far, but it is believed that through these gametes the different degrees of ploidy existing in the genus have been generated (Brandham 1969a; Castorena-Sanchez et al 1991; Ruvalcaba-Ruiz and Rodríguez-Garay 2002; Robert et al 2008). Stebbins (1971) observed in this genus the highest degree of chromosomal asymmetry existing in spermatophytes

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