Transcript Angiosperms II - University of Nebraska Omaha

Angiosperms II
Fruits, Seeds, and
Embryos
FRUITS
• A “fruit” is derived from the ripened
ovary (ovaries) and sometimes other
associated floral parts
– to end the debate then, a tomato is a fruit
since it is derived from a flower
• The fruit (usually a ripened ovary) is
surrounded by the fruit wall or pericarp
– This wall is composed of three layers
(exocarp, mesocarp, and endocarp)
– These layers may be distinct or fused
Fruit Structures (Pericarp)
Endocarp
Mesocarp
Exocarp
Fruit Types
For an interactive key to FRUIT TYPES, go to
http://arnica.csustan.edu/key/key2.html
• Multiple Fruits
– derived from
MANY flowers
– pineapple,
mulberry
Fruit Types (cont.)
• Aggregate Fruits
– derived from
SEVERAL
separate carpels
(pistils) of ONE
flower
– strawberry,
raspberry,
blackberry
Fruit Types (cont.)
• Simple Fruits
– derived from ONE carpel or pistil of ONE flower
– are either fleshy or dry at maturity
Simple Fruits
• Fleshy Fruits (a few types)
– with a fleshy hypanthium and/or receptacle =
pome (apple)
– a single seed with stony endocarp = drupe
(plum, peach)
– many seeded, endocarp fleshy = berry
(grape, tomato) or pepo (pumpkin,
watermelon)
– Outer layer with a separable rind =
hesperidium (orange, lemon, grapefruit)
Fleshy Simple Fruits
BERRY
DRUPE
Fleshy Simple Fruits (cont.)
PEPO
HESPERIDIUM
POME
Simple Fruits (cont.)
• DRY FRUITS
– Dehiscent Types
• seeds released through one seam = FOLLICLE
• seeds released through 2 seams = LEGUME
• seeds released though pores or multiple seams =
CAPSULE
– Indehiscent Types
• pericarp hard and thick with a basal cup = NUT
• Pericarp soft and thin, no cup = ACHENE,
CARYOPSIS etc...
Dehiscent Dry Fruits
CAPSULE
LEGUME
FOLLICLE
Indehiscent Dry Fruits
NUTS
ACHENE
Why the variation in fruit types?
• Fruits are units of
dispersal for the
seeds
• Certain fruits are
adapted for
dispersal by wind
(small, light,
winged)
Fruit Dispersal (cont.)
• Others are dispersed by animals
(fleshy, colored, sweet, or high in
energy like nuts; or with spines, hooks)
Bidens – tickseed fuits
Fruit Dispersal (cont.)
• Some for water dispersal (coconut)
Seeds
• A seed is surrounded by the seed
coat derived from the integuments
• The embryo may have large
cotyledons (as in lima beans) and
little endosperm
• Some seeds have lots of endosperm
and thin cotyledons (castor beans)
Pinto Bean vs.
Castor Bean
The Grass Seed (Fruit)
• Outer pericarp is fused to the seed coat
• Single massive cotyledon is called the
scutellum
• Protective sheaths cover the early shoot
(coleoptile) and the root (coleorhiza)
• Endosperm is surrounded by a special
layer of cells called the aleurone layer
CORN GRAIN
coleoptile
endosperm
coleorhiza
scutellum
embryonic leaves
Seed Germination
• Normal germination requires proper
temperature, water, oxygen and
sometimes light
• If, given proper conditions, a seed does
not germinate, we say it is DORMANT
• Dormancy is annoying to us, but it is
evolutionarily adaptive for the plant
Reasons for Seed Dormancy
• Seed coat impervious to water and/or
oxygen (imbibition of water is often the
first step in germination)
– scarification required (physical or
chemical) to allow entry of water and/or
oxygen
– many commercial applications for seed
production
Seed Scarification
Seed
Dormancy
• Seed has an
immature embryo
• Seed has chemical
inhibitors in the
seed coat that must
be leached out
Desert in Bloom
Seed Longevity
• Seeds may be
dormant for only a
few weeks to
thousands of years
– record is over
10,000 years for
Arctic lupine seeds
from lemming
burrows
Seed Longevity (cont.)
– Lotus seeds
have been
germinated
after
storage for
more than
2,000 years
Seed Banks
• Seed Banks help protect angiosperm
genetic diversity around the world
Kew Gardens,
England. Home of
the Millennium
Seed Bank Project
Embryology
• Early embryo
development in plants
progresses through
specific stages:
– much of the work done on
Capsella bursa-pastoris
(“shepherd’s purse”)
Capsella
Embryology
–“ball” stage with
basal cell,
suspensor and
the embryo
proper
Capsella
Embryology
(cont.)
– “heart-shaped”
stage where the
embryo’s two
cotyledons become
obvious and the
differentiation of
tissues become
evident
Capsella
Embryology
(cont.)
• “bending
cotyledons”
stage where
the embryo
moves toward
its final form
Capsella
Embryology
(cont.)
• “Mature
embryo”
stage
Embryonic Tissue Layers
• Thee distinct tissue layers differentiate
early in embryo development:
– PROTODERM which will give rise to the
plant’s epidermis and all associate
structures (guard cells, trichomes,
epidermal cells)
– PROCAMBIUM which will become the
primary xylem and phloem tissues
(vascular tissues)
Embryonic Tissue Layers (cont.)
– GROUND MERISTEM from which will be
derived the pith, cortex, and associated
structures in the stem and root
• These tissue layers correspond in a way
to early tissues in animal embryos,
namely, the ectoderm, endoderm, and
mesoderm
• Development of most plant embryos
has not been investigated