4. Seeds Flashcards
Formation of the embryo
Pollen sperm fertilizes the egg, resulting in a zygote
The zygote begins cell division and es polarity, up and a down
-Lower end forms a basal cell and stalk-like suspensors. Anchors the embryo at the micropyle end
-Upper end forms an apical cell, where most of the growth comes from
Differentiation of the embryo
Occurs through different planes of cell division
Protoderm becomes the epidermis
Vertical cell division leads to the ground meristem and the procambium( precursor to xylem and phloem)
Stages of Seed Development in Dicots:
- Globular Stage
* Suspensor – anchors embryo and absorbs food from endo sperm
* Basal cell
* Proembryo – becomes the embryo, then the seed - Heart shaped stage
- Torpedo stage
- Mature embryo
Integument
seed coat
Funiculus
stalk of the ovule
Hilum
scar where the funiculus was attached
Micropyle
opening in the integument of the ovule through which the pollen tube enters the embryo
Epicotyl
embryonic shoot
Plumule
becomes stem and leaves
Hypocotyl
region between the shoot and the root
Radicle
embryonic root
Cotyledon
contain stored food
Endosperm
contains stored food outside the embryo but inside the seed coat
Scutellum
specialized cotyledon in grasses
Coleoptile
sheath of the shoot
Coleorhiza
sheath of the radicle
Hypogean development
cotyledons remain below ground
Epigean development
cotyledons above ground
Parts of a dicot seed
Endosperm- absorbed by developing embryo
Fleshy cotyledons
Micropyle
Hilum
Seed coat
Parts of a monocot seed
Pericarp
Endosperm
Scutellum
Coleoptile
Plumule
Radicle
Coleorhiza
Role of the testa
Provides protection
Critical in monitoring water uptake during seed germination
Seed maturation – what occurs?
- Huge amounts of starch, oils, and proteins in endosperm, perisperm, cotyledons
- Desiccation, loss of 90% of its moisture
- Seed coat hardens
- Some are quiescent, resting until exposed to water, some are dormant, won’t grow without special environmental signals, cold or photoperiod
Quiescent
A state of inactivity caused by unfavorable external environmental conditions. A seed that does not germinate because the soil is too dry
Dormant
A state of inactivity caused by internal physiological factors, regardless of favorable environmental conditions. A seed that won’t germinate even in optimal soil and moisture conditions because it requires a period of cold stratification.
Seed germination process –what happens and how does it happen? When is germination complete?
Period between resting and growth stages of the plant
Requires- water, oxygen, and suitable temperature
Most vulnerable stage
Radicle emergence signals the end of germination
