plant Development - 1

plant Development - 1

Seed dormancy occurs during:

Seed dormancy is established and maintained during maturation stage of embryogenesis after heart and torpedo phases when embryo growth ceases and expansion growth stops completely. During maturation ABA accumulates inducing late embryogenesis abundant proteins, oleosins, storage proteins, lipids, and desiccation tolerance mechanisms while gibberellin signaling is suppressed and seed coat hardens imposing physical coat dormancy. Maternal and embryonic factors impose dormancy preventing precocious germination vivipary ensuring effective dispersal and survival through unfavorable season. Germinat

Ref: Finkelstein et al., Plant Physiol 2002; Bewley: seed dormancy established during maturation stage via ABA and LEA proteins.

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plant Development - 1

Cells degrading after fertilization in embryo sac:

Following double fertilization and early embryogenesis, embryo sac undergoes extensive remodeling via programmed cell death of unnecessary attraction cells. Two synergid cells that synthesized LURE peptides guiding pollen tube usually degenerate rapidly upon tube arrival preventing additional tubes via ethylene and FERONIA-mediated polyspermy block, and antipodal cells at chalazal pole degenerate quickly after fertilization, though persist longer in cereals providing transient nutrition support. Their coordinated degradation recycles valuable nutrients and eliminates residual attraction signal

Ref: Mathew & Prasad, Bot Rev; Drews: synergids and antipodals degrade after fertilization via programmed cell death.

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plant Development - 1

Callose enzyme secreted by:

Callose envelope of β-1,3-glucan surrounding pollen mother cells and tetrads must be rapidly degraded to liberate free microspores for pollen wall development. Enzyme responsible callase β-1,3-glucanase is actively synthesized and precisely secreted by tapetum layer of anther wall under transcriptional regulation of AMS, MS1, TDF1, and MYB80 factors. Secreted callase hydrolyzes callose allowing microspore expansion, primexine formation, and sporopollenin deposition forming characteristic exine pattern. Disruption of tapetal secretion causes tetrad persistence and complete male sterility, highl

Ref: Scott et al., Plant Physiol; Frankel: tapetum secretes callase enzyme hydrolyzing callose tetrad walls releasing microspores.

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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.

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plant Development - 1

Dominant generation in angiosperms:

Dominant generation in angiosperms is diploid sporophyte phase comprising conspicuous plant body with true roots, stems, leaves, vascular tissues, and flowers. Massive sporophyte produces via meiosis haploid spores that develop into highly reduced gametophytes: male pollen grain of two-three cells and female embryo sac of seven cells entirely dependent on sporophyte for nutrition, protection, and desiccation resistance. After double fertilization diploid embryo and triploid endosperm develop within seed borne on sporophyte. Sporophyte dominance reflects evolutionary adaptation providing protec

Ref: Taiz & Zeiger, Plant Physiology: sporophyte is dominant multicellular generation in angiosperm life cycle providing protection.

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plant Development - 1

Embryo sac consists of:

Embryo sac in Polygonum-type typical of approximately seventy percent angiosperms consists of seven cells organized around eight nuclei arising from three sequential free nuclear mitoses of functional megaspore without initial cytokinesis. Configuration comprises micropylar egg apparatus with two synergids flanking egg cell, large central cell with two polar nuclei occupying huge central vacuole, and chalazal three antipodal cells often ephemeral. This precise seven-celled eight-nucleate organization positions egg for fertilization, synergids for pollen tube attraction, central cell for endosp

Ref: Drews & Koltunow, Arabidopsis Book 2011: typical embryo sac seven cells eight nuclei Polygonum-type organization.

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plant Development - 1

Nucellus is primarily a:

Nucellus constitutes central parenchymatous tissue of ovule derived from megasporangium forming massive bulk surrounding and protecting megaspore mother cell and later embryo sac. It serves primarily as nutritive tissue providing carbohydrates, amino acids, lipids, and hormonal cues to developing female gametophyte through apoplastic and symplastic transport pathways. Depending on crassinucellate or tenuinucellate configuration degree of tissue development may be substantial. After fertilization nucellus generally degenerates, but may occasionally persist as perisperm storage tissue in beet, p

Ref: Mohammad et al., Seed Sci; Reiser & Fischer: nucellus is nutritive tissue surrounding and feeding embryo sac.

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plant Development - 1

Angiosperm gametophytes develop from:

Angiosperm gametophytes develop from haploid spores produced within sporangia located in third and fourth floral whorls according to classical ABC model. Third whorl stamens produce microsporangia generating male gametophytes pollen grains, while fourth whorl carpels form megasporangia ovules generating female gametophytes embryo sac. First whorl sepals and second whorl petals are sterile protective and attractive structures aiding pollination and preventing desiccation. This organization directly links MADS-box floral organ identity patterning to gametophyte generation location, elegantly coo

Ref: Coen & Meyerowitz, Nature; Goldberg: angiosperm gametophytes develop from third whorl anthers and fourth whorl carpels.

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plant Development - 1

Tapetum functionally provides:

Tapetum is specialized innermost anther wall layer directly surrounding sporogenous tissue undergoing differentiation into secretory or amoeboid forms during anther development. Its functional role involves providing nourishment to developing microspores and pollen grains through synthesis and active secretion of enzymes, sporopollenin precursors, Ubisch bodies, pollenkitt, tryphine lipids, flavonoids, and self-incompatibility recognition proteins. It precisely regulates callose degradation via callase secretion and undergoes programmed cell death depositing materials onto exine forming protec

Ref: Pacini et al., Can J Bot 1985; Goldberg: tapetum provides nourishment and sporopollenin to developing pollen grains.

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plant Development - 1

Meiosis in microsporogenesis occurs in:

Meiosis in microsporogenesis occurs specifically in diploid microspore mother cells also called pollen mother cells within anther locules surrounded by nutritive tapetum layer and middle layers. These cells undergo meiosis I with homologous chromosome separation and meiosis II with sister chromatid separation generating haploid tetrads of microspores encased in callose walls ensuring genetic recombination and chromosome reduction halving genome ploidy. Tetrads subsequently separate after enzymatic callase action secreted by tapetum. Resulting microspores differentiate into pollen grains via mi

Ref: Scott et al., Arabidopsis Book: meiosis in microsporogenesis occurs in microspore mother cells within anther.

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plant Development - 1

Perfect flower refers to:

Perfect flower also termed hermaphroditic or bisexual contains both functional androecium with stamens producing pollen and gynoecium with carpels producing ovules within same receptacle irrespective of presence or absence of perianth whorls sepals and petals. Such flowers possess both male and female reproductive organs capable of self-pollination or outcrossing regulated by dichogamy, herkogamy, and self-incompatibility systems distinguishing sporophytic versus gametophytic control. Perfect condition distinguishes from imperfect unisexual flowers in monoecious or dioecious species where sepa

Ref: Mauseth, Botany: perfect flower contains both male androecium and female gynoecium within same flower.

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plant Development - 1

Fruit formation involves development of:

Fruit formation predominantly involves development of ovary after successful fertilization triggered by hormonal signals including auxin, gibberellin, and cytokinin produced by developing seeds preventing abscission zone activation and stimulating cell division and expansion programs. Ovary wall differentiates into pericarp comprising exocarp, mesocarp, and endocarp whose texture, lignification, and sugar content define fleshy drupes and berries versus dry dehiscent or indehiscent pods. Accessory tissues like receptacle may contribute forming pome or aggregate fruits. Maturation ensures coordi

Ref: Gillaspy et al., Plant Cell 1993: fruit formation involves ovary development after fertilization driven by auxin/GA signals.

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