Alternation of Generations:
Diploid = sporophyte - produces spores (mega and microspores) by
meiosis
Haploid = gametophye - produces gametes by mitosis
female gametophyte = embryo sac
male gameotophyte = pollen grain mitosis
mitosis
Figure 1.1
1
•Megaspore divides mitotically to form 8 nuclei, that
cellularize to form 7 cells (central cell is binucleate)
•microspore divides to produce tube cell and generative cell
•Generative cell divides to form 2 sperm cells
2
Double fertilization generates zygote and endosperm:
•1 sperm fuses with egg cell to form zygote
•2nd sperm fuses with 2 nuclei of central cell to form triploid endosperm
Figure 1.1
Embryo develops apical/basal and radial polarity:
Cotyledons, hypocotyl, radicle, Root and shoot meristems
Epidermis, ground meristem, procambium
Figure 1.2
3
Germination: epigeal (e.g. Arabidopsis) - elongation of
hypocotyl raises cotyledons above ground
Hypogeal (e.g. pea) - elongation of epicotyl,
cotyledons stay on/below ground
Figure 1.3
Primary Vegetative and reproductive development
Figure 1.4
4
Root apical meristem (RAM)
Figure 1.5
Protoxylem/phloem - differentiates during elongation
Metaxylem/phloem - differentiates after elongation
Endodermis - contains casparian strip
Pericycle - meristematic - forms lateral roots (adventitious
shoots
Shoot Apical Meristem (SAM):
•Central zone (CZ) - large, slow division
•Peripheral zone (PZ) - small, fast division
•Tunica (anticlinal), corpus (all directions)
Figure 1.6
5
Dicot Leaf formation:
time between leaf initiation = plastochron
Position of leaves = phyllotaxy
adaxial
abaxial
Figure 1.7
Secondary
development:
•Vascular cambium
(ray and fusiform)
•Cork cambium
Figure 1.9
6
Reproductive development;
Transition from vegetative to flowering
heteroblasty
Figure 1.10
Floral development:
Meristem (SAM or lateral) produces modified leafy
organs (sepals, petals, stamens and carpels)
Figure 1.11
7