Morphology, Vascular Anatomy and Embryology of Pistillate and Staminate Flowers of Asparagus Officinalis

Abstract

Flowers of three pistillate (female), two heterogametic staminate (male) and two homogametic male genotypes of Asparagus officinalis L. were compared for morphology and vascular anatomy of the flower and for embryological development to the stage of mature ovules and pollen. Flowers are liliaceous, the staminate with rudimentary pistils and the pistillate with collapsed anthers. The uncomplicated vascular pattern differs between staminate and pistillate flowers only in the size and degree of maturation of bundles to stamens and carpels. Longer styles appear to be correlated with a greater extent of ovule development in ovaries of staminate flowers. Microsporogenesis in males is normal with wall development corresponding to the Monocotyledonous type. The tapetum is glandular and binucleate, cytokinesis successive, the tetrads isobilateral or occasionally decussate, and the mature pollen grain two‐celled. A pair of heteromorphic, possibly sex, chromosomes was observed in heterogametic male plants. Anther development is initially the same in pistillate flowers, but the tapetum degenerates precociously followed by collapse of microspore mother cells. In pistillate flowers the ovules are hemitropous, bitegmic, and slightly crassinucellate. Megasporogenesis‐megagametogenesis conforms to the Polygonum type. In staminate flowers ovule development is like that in pistillate flowers until degeneration starts in nucellar and integumentary cells at the chalazal end. Ovules in both homogametic male genotypes rarely complete meiosis, while in the heterogametic males it is normally completed with about one ovule in 20 flowers forming a mature megagametophyte. Since manipulation of sex expression in Asparagus could be important in developing inbred male and female lines for breeding purposes, those aspects of the morphological and embryological observations presented which might be useful in planning experiments to induce sex changes are discussed briefly.

Subdioecy in Consolea spinosissima (Cactaceae): breeding system and embryological studies

“…24, stages 7-8). Very similar timing for sex determination (and sexual morphs) was found in the ''dioecious'' Asparagus officinalis L. (Lazarte and Palser, 1979). In this system, sexual determination is based on sex chromosomes.…”

“…In this system, sexual determination is based on sex chromosomes. The staminate plants are either heterogametic XY or homogametic YY, and pistillate plants are homogametic XX (Lazarte and Palser, 1979). These three sexual morphs appear to be analogous to the weak hermaphrodite, male, and female morphs of C. spinosissima, respectively.…”

“…This abortion was evidenced by the degeneration of the nucellar cells that lie adjacent to the megagametophyte cavity and the megagametophyte. Ovule abortion in Asparagus officinalis starts in the sterile tissues of the ovule, i.e., the nucellar cells at the chalazal end and the integuments, and proceeds towards the megagametophyte (Lazarte and Palser, 1979). In C. spinosissima, both events are apparently simultaneous.…”

Sex Determination in Flowering Plants

“…Flower buds from females and males are phenotypically indistinguishable until th.e onset of meiosis (Lazarte and Palser, 1979;Bracale et al, 1991). At this time, pollen formation is arrested in female flowers and embryo sac formation is arrested in male flowers, so that the mature flowers are functionally unisexual.…”

“…At this time, pollen formation is arrested in female flowers and embryo sac formation is arrested in male flowers, so that the mature flowers are functionally unisexual. It appears that the defect in stamen maturation in pistillate flowers is the precocious degeneration of the tapetal cells and the collapse of the microspore mother cells; in staminate flowers, degeneration begins in nucellar and integumentary cells and progresses to the megaspore mother cell (Lazarte and Palser, 1979). There is some variation in the timing of megaspore degeneration that may be genotype dependent.…”