Vegetative Plant DevelopmentChapter 37

Embryo DevelopmentBegins once the egg cell is fertilized-The growing pollen tube enters angiosperm embryo sac and releases two sperm cells-One sperm fertilizes central cell and initiates endosperm development (nutrients for embryo)-Other sperm fertilizes the egg to produce a zygote-Cell division soon follows, creating the embryo

Embryo DevelopmentThe first zygote division is asymmetrical, resulting in two unequal daughter cells -Small cell divides repeatedly forming a ball of cells, which will form the embryo-Large cell divides repeatedly forming an elongated structure called a suspensor-Transports nutrients to embryoThe root-shoot axis also forms at this time -Roots near suspensor cells and shoots at other end.

How do plants divide assymetrically in the first place?

Sperm entry point, light, gravityMain body = thallusAlgae anchor = RhizoidThis is all information gathered from brown algae!!

Development of Body PlanIn plants, three-dimensional shape and form arise by regulating cell divisions-The vertical axis (root-shoot axis) becomes established at a very early stage-Cells soon begin dividing in different directions producing a solid ball of cells-Apical meristems establish the root-shoot axis in the globular stage

Development of Body PlanThe radial axis (inner-outer axis) is created when cells alternate between synchronous cell divisions-Produce cell walls parallel to and perpendicular to the embryos surfaceThe 3 basic tissue systems arise at this stage-Dermal, ground and vascular tissue established

Some Genes Involved in Root-Shoot FormationBoth shoot and root meristems are apical meristems, but are independently controlled-Shootmeristemless (STM) is necessary for shoot formation, but not root development -STM encodes a transcription factor with homeobox regionCotyledons not mature leavesare shown

Some Genes Involved in Root-Shoot FormationThe HOBBIT gene is required for root meristem, but not shoot meristem formation

Hobbit is a protein that inhibits another protein that stops the gene expression of the genes that Auxin causes to be made!!!!

Auxin and Monopteros Promote Root DevelopmentOne way that auxin induces gene expression is by activating the MONOPTEROS (MP) protein-Auxin releases the repressor from MP-MP then activates the transcription of a root development gene

Two Internal Proteins Responsible for the Development of a Structure Cause Similar Phenotypes if their corresponding genes are mutatedHas a basal peg not a rootAbnormal celldivision create stubrather than a root

Developmental Changes During the Globular StagePrimary meristems differentiate while the plant embryo is still at the globular stage...THERE ARE 3 PRIMARY MERISTEMS-No cell movements are involvedThe outer protoderm develops into dermal tissue that protects the plantThe ground meristem develops into ground tissue that stores food and water The inner procambium develops into vascular tissue that transports water & nutrients

MorphogenesisThe heart-shaped globular stage gives rise to bulges called cotyledons-Two in eudicots and one in monocotsThese bulges are produced by embryonic cells, and not by the shoot apical meristem-This process is called morphogenesis-Results from changes in planes and rates of cell division

More Morphogenesis Changes-As development proceeds, the cells with multiple potentials are restricted to the meristem regions

-Many meristems have been established by the time embryogenesis ends and the seed becomes dormantDuring embryogenesis, angiosperms (Flowering plants) undergo three other critical events: -Storage of food in the cotyledons or endosperm-Differentiation of ovule tissue to form a seed coat-Development of carpel wall into a fruit

Endosperm InformationEndosperm varies between plants-In coconuts it is liquid-In corn it is solid

-In peas and beans it is used up during embryogenesis

-Nutrients are stored in thick, fleshy cotyledons

Seeds-In many angiosperms, development of the embryo is arrested soon after meristems and cotyledons differentiate

-The integuments develop into a relatively impermeable seed coat

-Encloses the seed with its dormant embryo and stored food

SeedsSeeds are an important adaptation because:1. They maintain dormancy under unfavorable conditions2. They protect the young plant when it is most vulnerable3. They provide food for the embryo until it can produce its own food4. They facilitate dispersal of the embryoSEED FACTSOnce a seed coat forms, most of the embryos metabolic activities ceaseGermination cannot take place until water and oxygen reach the embryoSeeds of some plants have been known to remain viable for thousands of years

Styles of Seed GerminationSpecific adaptations ensure that seeds will germinate only under appropriate conditions-Some seeds lie within tough cones that do not open until exposed to fire

Styles of Seed Germination-Some seeds only germinate when sufficient water is available to leach inhibitory chemicals from the seed coat

-Still other seeds germinate only after they pass through the intestines of birds or mammals

Pistils = One or more CarpelsCarpels = Stigma, Style & OvaryThe ovary wall is termed the pericarp

-Has three layers: exocarp, mesocarp and endocarp

-One, some, or all of these layers develop to recognized fruitFruits can be:-Dry or fleshy-Simple (single carpel), -Aggregate (multiple carpels), -Multiple (multiple flowers)Fruits = Pistils...During Seed Formation Flower Develops into Fruit

In Dry Fruit (Like Legumes) the Pericarp Is Dry @ MaturityFruits have seeds!! (in general)

In Fleshy Fruits Like Tomatoes Pericarp Is Thicker

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FruitsDevelopmentally, fruits are fascinating organs that contain 3 genotypes in one package: -The fruit and seed coat are from the prior sporophyte generation-The developing seed contains remnants of the gametophyte generation (????) -The embryo represents the next sporophyte generation

Fruit Dispersal

-Ingestion and transportation by birds or other vertebrates-Hitching a ride with hooked spines on birds and mammals-Blowing in the wind-Floating and drifting on water

GerminationGermination is defined as the emergence of the radicle (first root) from the seed coatGermination begins when a seed absorbs water & oxygen is available for metabolism-Often requires an additional environmental signal such as specific wavelength of light

Releasing Sugars From Cotyledon...So the Embryo Can Grow

Releasing Sugars From Cotyledon...So the Embryo Can GrowEmbryo produces gibberellic acid-This hormone signals the aleurone (outer endosperm layer) to produce a-amylase-Breaks down the endosperms starch into sugars that are passed to embryo

GerminationNew growth comes from delicate meristems As the sporophyte pushes through the seed coat, it orients with the environment such that the root grows down & shoot grows up-Usually, the root emerges before the shoot-The shoot becomes photosynthetic, and the postembryonic phase is under wayCotyledons may be held above or below the ground-May become photosynthetic or shrivel

Germination