Transcript CB098-008.42_Seeds_&_Fruit_A

Seeds & Fruits
A Seed is a mature
ovule, which
contains the
embryo plant for
the next
generation.
A Fruit is a mature
or ripened ovary.
A fruit is the
packaging
structure around
the seed.
Seeds
Seed- A matured
ovule without
accessory parts.
Remember, the
ovule surrounds
the female
gametophyte.
Onion Seeds
Remember from the flower chapter that double
fertilization occurs.
A) The zygote (2n) becomes the embryo (2n).
B) The primary endosperm becomes the
endosperm.
Remember that the endosperm is the nutrient
rich storage tissue that will feed the seed when it
germinates. Endosperm is common in
monocots and remains in the seed as a food
reserve. This food is absorbed through
epidermal cells for food for the embryo.
Endosperm is not common in dicots. In dicots,
the endosperm’s energy is transferred to
cotyledons (seed leaves) as the seed forms
(matures).
Cotyledons
Cotyledon – seed leaf; there are two in the embryo/seedling of
dicotyledonous plants (dicots) they generally store food and can expand
and become photosynthetic; in monocotyledonous plants (monocots),
only one cotyledon is present, generally a digestive organ.
Monocots have 1 leaf
emerge from the embryo.
This is the coleoptile.
Monocots, later, often have
parallel venation on leaves,
sheaths instead of petioles
and usually no secondary
growth. Examples: Lily,
Corn, Onion, Grasses
Dicots have 2
seed leaves
emerge from the
embryo. Dicots
include the
eudicots,
magnoliids, and
a few basal
angiosperms.
Embryo & Seed Development in Cotton
The zygote goes
through mitosis to
form the
proembryo and
suspensor
(supports embryo
in endosperm).
The cotton
seed has a
seed coat and
contains the
mature ovule
(mature
embryo within).
The
Embryo
Develops.
In the seed, the
radicle
(embryonic root)
is at one end
and the shoot
tip is at the
other end.
The Cotyledons
Form. These are
seed leaves that
store food. After
germination,
cotyledons expand
and become
photosynthetic.
Onion Seed (A Monocot)
Seed Structures
Note: Seed structures do vary.
Raphe – ridge on seeds, formed by
the stalk of the ovule.
Hilum – Large scar left when the seed
breaks away from its placental
connections (the seed’s belly button).
Micropyle – This is where the pollen
tube entered the ovule.
Notice that this dicot does not have
endosperm, which is typical for the
majority of dicots.
Radicle – embryonic root (1st Root to
emerge & first structure to emerge
from seed as well).
Epicotyl – after seed germination,
this is the portion of the embryonic
shoot that will be above cotyledons.
Hypocotyl – after seed germination,
portion of the embryonic shoot below
the cotyledons but above the radicle.
Common
Bean
Castor Bean
(A Dicot with Endosperm)
Caruncle – A spongy outgrowth of the seed coat that absorbs water,
which is necessary for germination.
Yellow Foxtail Grass
(A Monocot)
The seed of grasses is joined to its
fruit. This is called the grain or
caryopsis.
Coleoptile – the first leaf in
germination of monocots that
sheaths the succeeding leaves;
ensheathes the shoot apex.
Food is transferred from the
endosperm to the scutellum to the
growing embryo.
Germination
Germination is the beginning or resumption of
growth of a seed, spore, bud, or other resting
structure. Germination starts the metabolism
of stored food (endosperm or cotyledons) in
the seed.
1) The first step of germination is imbibition (the
uptake of water). Seeds by themselves are
very dry (only 5-10% water).
2) After imbibition, the swelling of the radicle
(embryonic root) starts first and bursts the
seed coat.
The Germination Process Differs Among Plants
Stages in
the Epigeal
Germination
of a Bean
Seed (Dicot).
Epigeal Germination – The hypocotyl raises the cotyledons and
shoot apex towards the light. The cotyledons emerge from the
soil and become leaf-like photosynthetic structures.
Note: The Hypocotyl
(below cotyledons)
elongates first.
Stages in the Hypogeal Germination of a Pea Seed (Dicot).
Hypogeal Germination – The epicotyl straightens, the
cotyledons remain below ground and only the apex and
first leaf are raised upward.
Note: The Epicotyl (above cotyledons) elongates &
hypocotyl (below cotyledons) remains below ground.
Stages in the Germination of an Onion Seed (Monocot).
From a previous slide during this chapter, we saw an onion seed diagram. Onion
seeds have a single coiled cotyledon.
Note:
The first
leaves will
start at the
base of the
cotyledon.
Stages in the Germination of a Corn Seed (Monocot).
After the primary root emerges, it branches to form the root system. Adventitious roots
emerge from the lower stem and prop roots form to hold the stem upright. The
emerging young leaves are protected by a sheathing-like coleoptile.
Note: The
Coleoptile is
the emerging
sheath that
protects the
shoots. The
Coleorhiza is
an emerging
sheath,
which
protects the
roots. The
primary root
rapidly
pushes
through the
coleorhiza.
Germination May Be Delayed By Dormancy
Dormancy - Growth and Development are temporarily suspended.
During dormancy, seeds have reduced physiological activity.
Some seeds remain
dormant and can later be
viable for long periods of
time (Some up to 100
years). The Oriental Lotus
seeds have been known to
last 1000 years in a
dormant state and then be
viable.
Different Items Can Break Dormancy
Some simply need just a little water. Lettuce needs light. Some legumes,
locust for example, need heavy scaring of their seed coats. Some need
moisture and freezing temperatures at correct levels and times. Certain pines
will not germinate unless they have been subjected to the rather high heat of a
fire.
BIO 141 Botany with Laboratory
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