Seed and embryo development Flashcards
What are Spermatophytes?
Seed plants
When did reproduction by seeds appear?
About 360 million years ago.
What are the advantages of producing seeds?
*Seeds don’t have to germinate instantly they can wait for the *right conditions
*they are easily dispersed
*they are not digested by animals
*They have a protective case
Describe the parts of the flower
Peduncle: This is the stalk of the flower.
Receptacle: It is that part of the flower to which the stalk is attached to. It is small and found at the centre of the base of the flower.
Sepals: These are the small, leaf-like parts growing at the base of the petals. They form the outermost whorl of the flower. Collectively, sepals are known as the calyx. The main function of the calyx and its sepals is to protect the flower before it blossoms(in the bud stage).
Petals: This layer lies just above the sepal layer. They are often bright in colour as their main function is to attract pollinators such as insects, butterflies etc to the flower. The petals are collectively known as the corolla.
Stamens: These are the male parts of a flower. Many stamens are collectively known as the androecium. They are structurally divided into two parts:
Filament: the part that is long and slender and attached the anther to the flower.
Anthers: It is the head of the stamen and is responsible for producing the pollen which is transferred to the pistil or female parts of the same or another flower to bring about fertilization.
Pistil: This forms the female parts of a flower. A collection of pistils is called the gynoecium.
Learn more about Inflorescence here.
Pistil consists of four parts;
Style -is a long slender stalk that holds the stigma. Once the pollen reaches the stigma, the style starts to become hollow and forms a tube called the pollen tube which takes the pollen to the ovaries to enable fertilization.
Stigma– This is found at the tip of the style. It forms the head of the pistil. The stigma contains a sticky substance whose job is to catch pollen grains from different pollinators or those dispersed through the wind. They are responsible to begin the process of fertilization.
Ovary – They form the base of the pistil. The ovary holds the ovules.
Ovules– These are the egg cells of a flower. They are contained in the ovary. In the event of a favorable pollination where a compatible pollen reaches the stigma and eventually reaches the ovary to fuse with the ovules, this fertilized product forms the fruit and the ovules become the seeds of the fruit.
Describe the spermatophyte life cycle
Meiotic division of the megasporocyte (female) and microsporocyte (male) gives rise to spores.
Spores divide into gametophytes (male and female), which produce sperm and egg, plus additional cells.
The gametophytes (female and male)
Female= nucleus will divide 3 times (8 nuclei in total)
cellularization- cells form around the nuclei.
-the egg cell
-the central cell, either two or a fused one with two female genomes (polar nuclei)
male=only 2 rounds of division
first is asymmetric to form a small and a big cell.
big cell is know as a tube cell
smaller cell will divide into two sperm cells
Double fertilisation in angiosperms
What does the pollen tube do?
What does double fertilisation generate?
The pollen tube brings the sperm cells to the embryo sac (female gametophyte).
In angiosperms, double fertilisation generates the diploid zygote and triploid endosperm.
there is a normal fertilisation using the first sperm cell and a nucleus but then there is also double fertilization as the second sperm cell fertilizes the central cell nucleus
From fertilisation to fully mature seed, what are the steps?
Embryo morphogenesis
Reserve accumulation
Desiccation
Late maturation
Early seed development
The nucleus of the fertilised central cell divides rapidly, giving rise to the uncellularised endosperm.
Meanwhile, the embryo develops through normal cell division to a globe shape.
Endosperm cellularisation
Nuclei division and initiation of cellularisation
Cellularisation: formation of cell walls and cell division
What is the suspensor during embryo development?
The suspensor is a “umbilical cord” between the embryo and the mother plant.
Seed development and anatomy: dicots what are;
Cotyledon
Hypocotyl
Radicle
Testa
Epicotyle (or plumule)
Cotyledon = leaf-like structure of the embryo
Hypocotyl = embryonic stem linking cotyledons and radicle
Radicle = embryonic root
Testa = seed coat
Epicotyle (or plumule) = tissue that will develop into the shoot
Describe the seed coat in Arabidopsis
top layer (epidermal layer) Mucilaginous epidermal cells
Palisade layer (thick secondary walls that can sometimes have lignin)
Parenchymatous cells
Endothelium layer
The seed coat (testa) is derived from the integuments surrounding the ovule and participates in the communication between seed and mother plant.
Seed development and anatomy: monocots
Name parts
Pericarp = remnant of the ovary surrounding the seed
Nucellar Projection = remnant of the ovule
Aleurone = external layer of the endosperm
Embryo
Cellularised Endosperm
Chlorenchyma layer
Vascular Tissue
In most monocots, reserves are stored mainly in the endosperm.
Endosperm development in cereals
The endosperm of cereals differentiates into starchy endosperm and aleurone cells.
