The specialized chalazal endosperm inArabidopsis thaliana andLepidium virginicum (Brassicaceae)

Abstract

Summary. Endosperm of the nuclear type initially develops into a large multinucleate syncytium that lines the central cell. This seemingly simple wall-less cytoplasm can, however, be highly differentiated. In developing seeds of members of the family Brassicaceae the curved postfertilization embryo sac comprises three chambers or developmental domains. The syncytium fills the micropylar chamber around the embryo, spreads as a thin peripheral layer surrounding a large central vacuole in the central chamber, and is organized into individual nodules and a large multinucleate cyst in the chalazal tip. Later in development, after the endosperm has cellularized in the micropylar and central chambers, the chalazal endosperm cyst remains syncytial and shows considerable internal differentiation. The chalazal endosperm cyst consists of a domelike apical region that is separated from the cellularized endosperm by a remnant of the central vacuole and a basal haustorial portion which penetrates the chalazal proliferative tissue atop the vascular supply. In the shallow chalazal depression of Arabidopsis thaliana, the cyst is mushroom-shaped with short tentacle-like processes penetrating the maternal tissues. The long narrow chalazal channel of Lepidium irginicum is filled by an elongate stalklike portion of the cyst. In both, the dome contains a labyrinth of endoplasmic reticulum, dictyosomes with associated vesicles, nuclei, and plastids. The basal portions, which lack the larger organelles, exhibit extensive wall ingrowths and contain parallel arrays of microtubules. The highly specialized ultrastructnre of the chalazal endosperm cyst and its intimate association with degrading chalazal proliferative cells suggest an important role in loading of maternal resources into the develaping seed.

Developing Seeds of Arabidopsis Store Different Minerals in Two Types of Vacuoles and in the Endoplasmic Reticulum

“…The chalazal domain has been described as a cyst of dense cytoplasm with haustorium-like extensions (Pacini et al, 1975;Mansfield and Briarty, 1990;Boisnard-Lorig et al, 2001) that could be involved in the transfer of nutrients from maternal tissues to the embryo (Nguyen et al, 2000). We have shown that as soon as the chalazal domain is established, the ER and vacuoles undergo extensive differentiation and transiently accumulate Mn and Zn, respectively.…”

“…In Arabidopsis and many other members of Brassicaceae, the transient endosperm consists of three domains: micropylar, central, and chalazal (Brown et al, 1999;Sørensen et al, 2001). The chalazal domain is located next to the vascular bundle of the maternal tissue and, in some species, differentiates into a cyst with haustorium-like extensions that can penetrate the adjacent tissues (Pacini et al, 1975;Vijayaraghavan and Prabhakar, 1984;Nguyen et al, 2000). As a result of these structural features, the chalazal endosperm domain has been assumed to play an important role in the loading of storage compounds from surrounding maternal tissues into the developing seed (Nguyen et al, 2000(Nguyen et al, , 2001.…”

Arabidopsis ETHE1 Encodes a Sulfur Dioxygenase That Is Essential for Embryo and Endosperm Development

“…4Ci) embryo. By the time the embryo has reached early globular stage, the endosperm, which consists of roughly 100 to 200 free nuclei, begins to cellularize, beginning first with the MCE and progressing through the PEN and CZE (Brown et al, 1999;Nguyen et al, 2000). Continued development of the embryo results in the early heart ( Fig.…”

Imprinting and Seed Development

“…The cyst sits atop the maternal nucellar proliferating tissue and underlying vasculature. Projections extend from the basal portion of the chalazal cyst into the maternal tissues (Nguyen et al, 2000). Imprinting may be particularly important in the CZE because of its direct connection with the female parent.…”