Sex organ determination and differentiation in the dioecious plant Melandrium album ( Silene latifolia ): a cytological and histological analysis

Abstract

Melandrium album (Silene alba) is a dioecious plant with heteromorphic sex chromosomes (XY system). Sexual dimorphism is a result of developmental blocks in male or female reproductive organ formation within young bipotential flower buds. Progress in understanding the genetic and molecular mechanisms controlling sex determination in this species relies on a detailed description of developmental timing in the two sexes, with emphasis on those early stages during which sexual dimorphism is established. We used a combination of histological and scanning electron microscopy analysis to refine the comparative study and description of the staging of male compared to female flower development. We show that (1) female dimorphism results from modifications in flower meristem organisation, namely a sudden arrest of cell divisions in whorl 4 of male flowers at the time when meristem partitioning is achieved between whorls 3 and 4, and (2) male dimorphism is part of the stamen differentiation process corresponding to stamen arrest at the early sporogenous stage in female flowers. Thus, Melandrium is a natural double "mutant" that is affected in very early and distinct processes of reproductive organ differentiation. Our results are used to discuss the most likely nature of the specific functions controlling sexual dimorphism in Melandrium.& k w d : Key words Dioecious plant · Melandrium album · Development · Sex determination · Organ differentiation& b d y :

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“…4-2, 3 and 4A). This is consistent with the reference literature (Farbos et al, 1997;Uchida et al, 2005;. Another quick way to determine the cutoff for Stage 8 floral buds during tissue collection was the appearance of trichome on the calyx.…”

“…Therefore the sepals were collected as the <1-mm group after all buds larger than 1 mm were removed. Based on our measurements, these buds were clearly Stage 8 (Farbos et al, 1997;Uchida et al, 2005;Uchida et al, 2003) or earlier in floral development (Fig. 4-2, 3 and 4A).…”

“…In the male plants we examined, the maturation of anthers from bilobal to tetralobal was the main change. The petal also started to (Farbos et al, 1997;Uchida et al, 2005;Uchida et al, 2003), the appearance of the gynoecium was consistent at each stage regardless of infection status; hence, this was used as the point of reference for staging. The primordia of the gynoecium appeared to be "mushroom"-shaped at Stage 6, as in the male bud ( Fig.…”

“…Preliminary transcriptome studies identified genes differentially expressed in the fungus during late stage infection of male flowers . (Farbos et al, 1997;Grant et al, 1994), in relation to bud size, and the corresponding fungal stages in infected floral tissue had previously been documented [but also see (Schäfer et al, 2010), for SEM images).…”

“…The definition of the stages was informed by graphical and text illustration of previouslypublished studies (Farbos et al, 1997;Uchida et al, 2005;Uchida et al, 2003).…”