Plant DevelopmentHow plant zygotes become embryos.How embryos are packaged in seeds.How fruits develop.How seeds germinate and embryosgrow.Double fertilization forms zygote (2N) andendosperm (3N)Zygote and endosperm go through mitosis tobecome many cellsBoth cell types derive nutrition from sporophyteparent during developmentDifferentiation begins at first division of thezygoteupper cell will become embryolower cell becomes suspensor and basal cell -each helps provide nutrients to developingembryoProembryo consists of three cell types -protoderm - becomes protective dermal tissueprocambium - gives rise to vascular tissueground meristem - givers rise to ground tissue - for foodand water storageGround meristem also gives rise to shoot and root apicalmeristems which establish the root-shoot axisEmbryonic cells give rise to cotyledons - “seed leaves”Root and shoot formationestablished during globular stage of developmentformation of each controlled independentlyMorphogenesisglobular stage gives rise to heart-shaped embryo with cotyledonsproduced by embryonic cellsEndosperm becomes loadedwith nutrients -carbohydrates, lipids, andproteinsnutrients are transferred toembryo through suspensorIn monocots, endospermremains in the mature seedIn dicots, the nutrition of theendosperm is transferred tothe cells of the cotyledonsand stored there. The maturedicot seed has little or noendosperm.The integuments of the ovulebecome the protective seed coat.A seed is a dormant resting stagewith very little metabolic activityMature seeds have very littlemoisture within them (< 20%)Some seeds can remain dormant for many years - soils commonlycontain a “seed bank” - a store of dormant seeds from many seasonsGermination often requires specific environmental cuesa specific amount of water, sunlight of proper wavelength, heatsome seeds have germination inhibitors that must be washed awaysome seeds require fire for germinationsome seeds require a period of cool temperatures prior to germination - “stratification”Fruits are derived from ovarian tissuesGermination begins with the absorption of water, and increase inmetabolic activity, and the cracking of the seed coatThe root emerges first to anchor plant.Elongation of the hypocotyl extends the shoot above ground.Cotyledons may be photosynthetic or remain below
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