Lecture 8: Plant development from seed to maturity

Plant Embryo division

begins with division of zygote

1st division is asymmetrical and transverse

apical cell: smaller cell on top, gives rise to most of the mature embryo

basal cell: larger cell, produces suspensor, anchors embryo at micropyle and is the source of nutrient exchange. Expands longitudinally by multiple transverse divisions to form the suspensor

Suspensor and hypophysis

produced by basal cell through multiple transverse divisions. Top cell of suspensor is the hypophysis

pro-embryo

8-cell stage

Protoderm, ground meristem, procambium

protoderm: becomes epidermis, periclinal divisions

ground Meristem: ""ground tissue, surrounds procambium

procambium: ""vascular tissue

Globular stage

cell division of the proembryo soon leads to the globular stage that is radially symmetrical and has little internal cellular organization, hypophysis formed

Heart stage

Cotyledon, cotyledon shoulder, central domain, hypophysis

Late Heart stage, Torpedo

Shoot apical meristem at the top, hypocotyl in the middle

Final stage with cotyledons

has SAM and RAM

Monocot vs Dicot Embryo

Monocot: 1 cotyledon

- plumule: becomes leaves

- hypocotyl: stemmy region below(hypo) cotyeldon

- radicle: becomes root, first tissue to emerge

- endosperm

-coleoptile: protective sheath

Dicot: 2 cotyledon

- plumule

- hypocotyl

- radicle

- endosperm

Germination

nutritional dependence (embryo)-> nutritional independence (roots and leaves)

Quiescence vs Dormancy

Quiescence: seed doesn't germinate because env conditions bad

Dormancy: seed doesn't germinate because needs a trigger

Dormancy Triggers

Light: Detects daylenth to avoid spawing in wrong season

Chilling(stratification): needs to be chilled to avoid spawnign in winter

Abrasion: needs to be abrased to germinate only after being dispersed

First structure to emerge post germination

radicle/root, anchor plant to soil, absorbs water,

then:

shoot

these exhaust nutrients from endosperm

Post germination

1) seed is imbibed and swells

2) GA induces hydrolytic enzymes, enzymes secreted

3) alpha amylase breaks down starch in endosperm to release root

4) Root emerges

5) shoot greens up

Epigeal vs Hypogeal

Epigeal: cotyledons above ground

Hypogeal: cotyledons below ground NEVER photosynthesize

Meristem

where plant grows from: area of continuous cell division

Primary vs secondary growth

Primary growth: vertical, occurs from SAM and RAM

Secondary growth: Girthiness, vascular cambium

SAM

at the top of the shoot, where meristem elongation occurs

stem from auxillary buds

Apical Dome

Apical shoulders: leaf primordia

Apical dome composed of protoderm, procambium and ground tissue

Plants grow up by:

elongating cells at the shoot tip