#embryo formation

plant Development - 1

Asymmetric division of zygote creates:

Asymmetric division of highly polarized zygote generates morphologically and molecularly distinct daughters: small apical cell dense with cytoplasm, mitochondria, nucleus destined to become embryo proper undergoing precise patterned divisions to form all plant tissues including shoot and root, and large basal cell highly vacuolated forming suspensor lineage connecting embryo to maternal tissues. Division creates apical and basal cells differing drastically in size, fate, and transcriptional programs including differential WOX2 versus WOX8/9 expression, PIN7 polarity, and auxin response, establ

Ref: Mansfield et al., Arabidopsis Atlas: asymmetric zygote division creates apical embryo cell and basal suspensor cell.

View Details

plant Development -ll

Hypophysis cell contributes to:

Hypophysis represents uppermost cell of basal lineage derived from basal cell after first highly asymmetric zygotic division; it resides at junction between suspensor file and embryo proper. It undergoes crucial asymmetric division generating lens-shaped quiescent center precursor and columella stem cell precursor, thus directly founding root meristem. Specification requires auxin flux from embryo proper via basal PIN1 polarity, MP-ARF5 mediated transcriptional response, and high auxin-induced PLT accumulation and WOX5 induction. Mutants lacking auxin perception in hypophysis exhibit horizonta

Ref: Mansfield & Briarty, Can J Bot 1991; Jürgens & Mayer: hypophysis cell contributes uppermost to root meristem formation.

View Details

Plant Breeding 2

Adventitious embryony involves embryo formation from:

Adventitious embryony represents sporophytic apomixis subtype where embryos originate directly from somatic diploid cells outside embryo sac, most commonly from nucellus layers or inner integument surrounding megagametophyte. Nucellar initial cell undergoes mitotic division triggered by somatic embryogenesis signaling involving LEC1, WUSCHEL and SOMATIC EMBRYOGENESIS RECEPTOR KINASE expression, protruding into embryo sac cavity and developing into embryo while still within ovule, leading to polyembryony where several nucellar embryos coexist with maybe one sexual zygotic embryo. Because embryo

Ref: Koltunow Plant Cell sporophytic apomixis nucellus; Esau Plant Anatomy adventitious embryony; NCERT Biology polyembryony Citrus example.

View Details

Plant Breeding 2

Non-recurrent apomixis produces embryos that are:

Non-recurrent apomixis rare phenomenon where meiosis proceeds normally producing haploid megaspores, but embryo develops from haploid egg without fertilization through haploid parthenogenesis. Resulting embryo possesses n chromosome number, hemizygous for all genes, exposing recessive lethals and causing severely reduced vigor, frequent albinism and complete male and female sterility because meiosis in haploid sporophyte unable to produce balanced gametes due to absence of homologous pairing leading to random chromosome segregation. Often accompanied by absent or defective endosperm causing se

Ref: Asker & Jerling Apomixis in Plants non-recurrent; Nogler Haploid parthenogenesis review; PubMed haploid apomixis sterility.

View Details

Plant Breeding 2

Recurrent apomixis produces embryos that are:

Recurrent apomixis termed diplosporous and aposporous types maintains chromosome number across cycles because embryo sac develops either from somatic nucellar cell dividing mitotically or from unreduced megaspore mother cell forming restitution nucleus after aborted meiosis. Egg cell therefore diploid containing full maternal chromosome complement 2n. Development proceeds parthenogenetically without fertilization, directly forming diploid embryo genetically identical to mother. Because ploidy same as maternal sporophyte, reproduction recurs stably, hence designation recurrent. Examples widespr

Ref: Nogler 1984 Gametophytic apomixis classification recurrent; Bicknell & Koltunow Review recurrent apomixis; Acquaah definition.

View Details