Exam 2 Part 2 Seed propagation Flashcards
What is a seed?
Sexual reproductive unit
The end product of a process of growth and development within the parent plant.
Sexual reproduction
Spores –e.g. ferns, horsetails
Seeds –Gymnosperms –Angiosperms
Seeds
Gymnosperms (~8,000 species)GNaked seeds –(lack ovary tissue covering seeds) Angiosperms (~250,000 species)GSeeds covered by ovary GTwo Classes or types of Angiosperms –Monocotyledonae –Dicotyledonae
Characteristics of a seed
–an embryo
–storage tissue or endosperm
–protective outer covering or seed coat
Embryo
–new “plant” from fertilization of female gamete by male gamete
–Multicellular organism
–Basic embryo structure: axis with growing points at the ends: radicle, shoot, and cotyledons
Cotyledons
–Embryonic leaves Angiosperms GMonocotyledons = one cotyledon GDicotyledons = two coytledons Gymnosperms Gcan have numerous cotyledons
Endosperm
Function… –Oils, Carbohydrates, and Proteins –Angiosperms Gendosperm, cotyledons, perisperm –Gymnosperms Gfemale gametophytic endosperm
Protective covering
Seed coat Gaka. testa (remains of nucellus (ovule tissue) & endosperm)GPhysical protection; exclude water and gases GUsually a good way to identify the species
seed formation generally requires two processes—pollinationand fertilization.
–Pollination: transfer of pollen within a single flower (self-pollination) or from separate flowers (cross-pollination) to a receptive stigma. –Fertilization: fusion of haploid (1n) male and female gametes inside the ovule.
Angiosperms
Male: Stamen: anthers and filaments
Female: Pistil: Stigma + Style + Ovary + Ovule
2 types of cell division
mitosis
meiosis
Mitosis
- Prophase: shortened and visible chromosome organization; chromosomes pair (genetic exchange) 2. Metaphase: Chromosome pairs line up at center plate3. Anaphase: pairs separate and move to polar ends 4. Telophase: chromosomes disperse; form two nuclei 5. Cytokinesis: division into two cells (full compliment of genetic information)
Angiosperm life cycle
OMature sporophyte (the plant) has male and female flower parts –Megaspores or ovules (1n) –microspores or pollen (1n) OPollination…–2 sperm nuclei released, double fertilization (unique to angiosperms) O1 sperm fertilizes the egg, (zygote) O1 sperm combines with two polar nuclei to form 3n nucleus, (endosperm)
3 stages of seed development
1st Histodifferentiation
2nd Cell expansion
3rd Maturation drying
1st histodifferentiation
–Differentiation of embryo and endosperm through cell division –Embryo reaches cotyledon stage –Weight increases rapidly
Typical dicot embryo development
- Proembryo 2. Globular 3. Heart 4. Torpedo 5. Cotyledon
Monocot embryo development
- Proembryo 2. Globular 3. Heart 4. Torpedo 5. Cotyledon
2nd cell expansion
–Accumulation of food reserves OWhere does this food come from? –Increasing production of DNA, RNA, protein synthesis
3rd maturation drying
–Reaches physiological maturity OStage of maximum dry weight OCan be removed from fruit and show high germination potential –Rapid water loss –Vascular connection with mother plant through funiculus is lost. OScar on seed coat after abscission (hilum)
seed types
orthodox
recalcitrant
Orthodox
OMetabolically active at maturity; in some sense of arrested state of growth OAble to withstand maturation drying OAllows the seed to be quiescent or dormant until conditions are right to germinate. OABA major signal induction OViable at 3 to 5%! Many plant tissues cannot tolerate below ~15 to 20% fresh weight
Recalcitrant
OMetabolically active at maturity OUnable to withstand maturation drying –Seeds must not dry below 30 - 50% moisture –Examples: avocado, cocoa, coconut, oaks, amaryllis
germination
stage of plant development following radicle emergence from the seed coverings, which leads to a seedling.
conditions required for initiation
1)Viable 2)Subjected to appropriate environmental conditions 3)Any primary (and/or secondary) dormancies overcome
