Download Angiosperm anatomy and development

Angiosperm anatomy and development
What is an angiosperm?
 Phylum Anthophyta
 A flowering plant
 Largest phylum of photosynthetic organisms
Two large classes
 Class Monocotyledones
– Grasses, orchids, cattails, palms
 Class Eudicotyldedones
– Trees, shrubs, herbs
Cotyledon
 A cotyledon is a seed leaf
 In monocots, it absorbs food from the endosperm
 In eudicots, it stores food
Early development
Chapter 22
Embryogenesis
 Embryogenesis is the formation of the embryo
 Establishes the body plan of the plant
– Apical-basal pattern
– Radial pattern
 Seed development happens at the same time
First division
 Determines polarity
 Apical cell
 Basal cell
Suspensor
 Basal cell becomes suspensor, which anchors the embryo at the micropyle
– Micropyle is the opening in the ovule through which the pollen tube enters
 Suspensor provides nutrients and hormones to embryo and is short-lived
Protoderm
 The future epidermis
Two additional tissue layers
 Procambium
 Ground meristem
Cell division
 Throughout the young embryo initially
 Becomes restricted to apical meristems
– In monocots, the apical meristem is found on one side of the cotyledon and
is surrounded by sheath
– In eudicots, the aplical meristem is found between the two cotyledons
Final seed formation
 Stalk called funiculus that connects ovule to ovary wall separates from the
ovule
– Forms scar called hilium
 Seed becomes dessicated
 Seed coat hardens
Seed anatomy
 In some seeds, only apical meristem occurs above the cotyledons
 In other seeds, an embryonic shoot called a plumule is found above the
cotyledons
– Plumule consists of stem-like epicotyl and apical meristem
 Below the cotyledons, is the stem-like hypocotyl and embryonic root or radicle
– Called hypocotyl-root axis if radicle is not distinguishable
Grasses
 Have large scutellum
 Coleoptile protects plumule
 Coleorhiza protects radicle
Seed germination
 Embryo resumes growing
 Germination is not possible until inbibition occurs
Seed dormancy
 In some plants, some degree of after-ripening must occur
– Low temperatures
– Scarification/mechanical stress
– Fire
– Digestion by animals
 After-ripening requirements closely linked to ecological conditions
Root
 First structure to emerge from seed in most plants
Shoot emergence
 Shoots emerge in different ways from different plants
 Epigeous
 Hypogeous
Epigeous
 Hypocotyl elongates and forms a “hook”
 Hook protects tender shoot until seedling reaches the soil surface
 Hook straightens out
 Cotyledons are carried out of soil
Epigeous germination
Epigeous germination
 In castor bean, cotyledons and endosperm are carried aboveground
Epigeous germination
 In onion, cotyledon elongates and carries endosperm above ground
Hypogeous germination
 Epicotyl elongates and forms hook to protect tender shoot
 Cotyledons stay in the soil since elongation occurs above them
Hypogeous germination
Hypogeous germination
 In grasses, coleoptile and coleorhiza emerge first
 Plumule and radicle emerge through these structures
Germination
 Germination to establishment are the most sensitive period in the life history of
the plant
– Seed predators
– Fungi
– Water