Anther, pollen and tapetum development in safflower, Carthamus tinctorius L

Abstract

In safflower, the anther wall at maturity consists of a single epidermis, an endothecium, a middle layer and the tapetum. The tapetum consists mainly of a single layer of cells. However, this single-layer appearance is punctuated by loci having 'two-celled' groupings due to additional periclinal divisions in some tapetal cells. Meiotic division in microsporocytes gives rise to tetrads of microspores. The primexine is formed around the protoplasts of microspores while they are still enveloped within the callose wall. Just prior to microgametogenesis, the microspores enlarge through the process of vacuolation, and the exine wall pattern becomes established. Microgametogenesis results in the formation of 3-celled pollen grains. The two elongated sperm cells appear to be connected. The exine wall is highly sculptured with a distinct tectum, columellae, a foot layer, an endexine and a thin intine. Similar to other members of the Asteraceae family, the tapetum is of the invasive type. The most novel finding of this study is that in addition to the presence of invasive tapetal cells, a small population of 'non-invasive' tapetal cells is also present. The tapetal cells next to the anther locules in direct contact with the microspores become invasive and start to grow into the space between developing microspores. These tapetal cells synthesize tryphine and eventually degenerate at the time of gametogenesis releasing their content into the anther locules. A smaller population of non-invasive tapetal cells is formed as a result of periclinal divisions at the time of tapetum differentiation. These cells are not exposed to the anther locules until the degeneration of the invasive tapetal cells. The non-invasive tapetal cells have a different cell fate as they synthesize pollenkitt. This material is responsible for allowing some pollen grains to adhere to each other and to the anther wall after anther dehiscence. This observation explains the out-crossing ability of Carthamus species and varieties in nature.

Embryology of Ageratum conyzoides L. and A. fastigiatum R.M. King & H. Rob. (Asteraceae)

“…Multinucleated amoeboidal tapetum is the most common type in Compositae (Johri et al 1992); it has also been observed in Carduoideae (Yeung et al 2011), Senecioneae (Pullaiah 1983;Lakshmi & Pullaiah 1987), Gnaphalieae (Davis 1962a;Pullaiah 1979), Astereae (Davis 1968), Anthemideae (Davis 1962b;Li et al 2010), Inuleae (Pullaiah 1979), and Heliantheae (Gotelli et al 2008). Secretory tapetum occurs in Pertyeae (Kapil & Sethi 1962), Cichorieae (Sood et al 2000;Yurukova-Grancharova et al 2006), and Vernonieae (Tiagi & Tamni 1963).…”

Cytological characterization of anther development in Panax ginseng Meyer

“…Development of male reproduction has been investigated extensively in rice (Oryza sativa) (Raghavan 1988;Zhang and Wilson 2009;Zhang et al 2011), Citrus sinensis (Koltunow et al 1995), Hibiscus syriacus (Kim and Kim 1995), Nelumbo nucifera (Kreunen and Osborn 1999), Arabidopsis (Arabidopsis thaliana) (Sanders et al 1999;Zhang et al 2002;Zhao 2009;Feng and Dickinson 2010;Chang et al 2011), Bromeliaceae (Sajo et al 2005), Onobrychis schahuensis (Chehregani et al 2008), Carthamus tinctorius (Yeung et al 2011), and maize (Zea mays L.) (Kelliher et al 2014). By contrast, few studies on anther development have been performed in the family Araliaceae even though there have been investigations on the morphological aspects of pollen grains.…”

Rice GLYCOSYLTRANSFERASE1 Encodes a Glycosyltransferase Essential for Pollen Wall Formation

“…Because intine synthesis is largely under the control of the microspore (Nakamura et al, 2010;Yeung et al, 2011), most genes related to intine development have been isolated from segregation-distorted mutants. In Arabidopsis, several genes involved in intine formation have been reported, including USP, RGP1, RGP2, and FLA3 (Drakakaki et al, 2006;Schnurr et al, 2006;Li et al, 2010b).…”

“…The intine that begins to develop has a composition similar to that of the primary wall of typical plant cells and includes cellulose, pectin, and various proteins (Noher de Halac et al, 2003;Li et al, 2010b). While the tapetum plays a pivotal role in exine formation, intine synthesis is largely under the control of the microspore (Nakamura et al, 2010;Yeung et al, 2011).…”