Plant Development Chapter 40_AP

Establishing a Seed Establishment of embryo Food supply is established Development continues and meristem regions are established Three basic tissue types are established Dermal, vascular, and ground Food supply is established Ovule tissue becomes transformed to hard protective covering Enters dormant phase

Early Cell Division First division is asymetrical Smaller daughter cell will become embryo Larger cell divides forming elongated suspensor Links embryo to nutrient tissue of seed Cells of embryo nearest suspensor become root

Establishing Tissues Three basic cell types established during globular stage Root-shoot axis Formation of root & shoot is independent Protoderm = dermal tissue Ground meristem = ground tissue Procambium = vascular tissue

Heart-shaped embryo & ball with single bulge Bulges are cotyledons Produced from embryonic cells Called morphogensis Food storage Sporophyte nutrients transferred to embryo via suspensor Endosperm is forming (double fertilization) In dicots, endosperm is used up & nutrients stored in cotyledons

Seed Formation Seed = embryo & stored food Early in development embryo stops developing Outer layers of ovule become seed coat Very stable in dormant state Germination cannot happen without water & oxygen

Seeds important adaptively Maintain dormancy under unfavorable conditions Maximum protection for vulnerable young plant Contain stored food to feed young plant until photosynthesis Adapted for dispersal

Specific adaptations ensure germination at right time Cones open when exposed to heat from fire Germinate in cleared habitat full of nutrients Inhibitory chemicals must be leached from seed coat Guaranteeing sufficient water Some must be ingested first weaken seed coat

Fruit Formation Three layers of ovary wall account for diversity of fruit types Three genotypes make complete fruit Fruit and seed coat from sporophyte endosperm Embryo Dispersal of fruit Fleshy covering = dispersed by birds/other animals Hooked spines = carried by animals Nuts = buried by squirrels Wings = air Floating seeds = water

Germination Begins when seed absorbs water Metabolism resumes Oxygen needs to be present for cellular respiration Imbibition is not enough Signals from environment still needed Light Series of cold days Series of days at right temperature

Requires utilization of amyloplasts Colorless starch storing plastids In grains, single cotyledon modified into scuttelum Food that is used up before endosperm Later, transfers nutrients from endosperm to embryo Root emerges and anchors young plant in soil, then shoot emerges