Early embryogenesis in Arabidopsis thaliana. II. The developing embryo

Abstract

Embryo differentiation in Arabidopsis thaliana follows the classical Capsella variation of the Onagrad type. Fertilization occurs approximately 3 h after flowering, whereupon vacuolar organization in the zygote changes and the cell elongates rapidly to approximately three times its original length. Cytoplasmic polarization is maintained. During the first two division steps there is very little increase in total cell volume, and during subsequent divisions vacuole number increases, with a concomitant decrease in size. Plastids remain undifferentiated up to the late globular stage, after which grana begin to develop. Ribosomal concentration increases significantly after fertilization. Differences between embryo proper cells become evident by the heart stage; vacuole, plastid, and mitochondrial abundance, size, and complexity vary within the embryo. There are no plasmodesmatal connections with the endosperm or integuments. Suspensor development is complete by the early globular stage, when it consists of seven to nine highly vacuolate cells, each linked by end wall plasmodesmata. Ribosome and volume densities of plastids and mitochondria are significantly lower than in the embryo proper organelles, and dictyosomes are infrequent. Embryo sac wall projections proliferate throughout the micropylar chamber, especially adjacent to the filiform apparatus and zygote base, and ingrowths form on the basal cell proximal wall. Key words: Arabidopsis, embryogenesis, embryo differentiation, wall ingrowths.

Arabidopsis floral homeotic gene BELL (BEL1) controls ovule development through negative regulation of AGAMOUS gene (AG).

“…t : dergoes meiosis, and one meiotic product develops into a seven-celled megagametophyte (26,27). The nucellus then degenerates, and the innermost cell layer of the integuments differentiates into the endothelium that surrounds the embryo sac (17).…”

Genome-Wide Association Mapping of Fertility Reduction upon Heat Stress Reveals Developmental Stage-Specific QTLs in Arabidopsis thaliana

“…This tag enabled us to relate the effect of heat stress to the developmental stage of the flowers and siliques along the inflorescence (Figure 2). In reference to the tag, all siliques received a relative position number and we subsequently defined five developmental regions, A to E. To link the observed reduction in silique length with the disruption of flower development and embryogenesis, we matched the regions as defined in Figure 2 with data regarding timing and order of events taking place during these developmental processes in Arabidopsis (Table 1; Smyth et al, 1990;Mansfield and Briarty, 1991;Schneitz et al, 1995;Sanders et al, 1999). Region A (silique position numbers 220 to 210) is linked to late embryogenesis.…”

“…This resulted in the identification of a candidate gene, QUASIMODO-LIKE2 (QUL2; Smyth et al (1990). b Data are taken from Mansfield and Briarty (1991), Schneitz et al (1995), and Sanders et al (1999). AT2G03480) that is highly expressed during the development of the male gametophyte (Honys and Twell, 2004).…”

Mutations in the FIE and MEA Genes That Encode Interacting Polycomb Proteins Cause Parent-of-Origin Effects on Seed Development by Distinct Mechanisms

“…For analysis of FIE::GFP and FIE::GUS expression in mature female gametophytes and to prepare pistils for reciprocal crosses, flowers were emasculated during stages 12A to 12C to prevent self-fertilization (Smyth et al, 1990;Christensen et al, 1997). Seed development was correlated to morphological changes occurring during endosperm and embryo development (Mansfield and Briarty, 1990a, 1990b, 1990cMansfield et al, 1990;Jurgens and Mayer, 1994). Intact unfertilized ovules and developing seeds from FIE::GFP transformants were excised, mounted in water, and observed immediately with a Zeiss Axioskop 2 fluorescence microscope (Carl Zeiss, Thornwood, NY) or an Olympus SZX12 fluorescence stereomicroscope (Olympus America, Melville, NY).…”