B.Sc. II Sem III Unit VI Development of Male Gametophyte

1. B.Sc.- II, Sem- III
Unit – VI
Embryology of Angiosperm
DR. SWATI PUNDKAR
ASSISTANT PROFESSOR
DEPARTMNET OF BOTANY
SHRI SHIVAJI SCIENCE COLLEGE,
AMRAVATI

2. .
Embryology is the study of structure and development of
embryo, including the structure and development of male
and female reproductive organs, fertilisation and similar
other processes.
Embryology played a significant role in consideration of
systemic botany.
Plant embryogenesis is a process that occurs after
the fertilization of an ovule to produce a fully developed
plant embryo
Plant embryology deals with study of all events starting
from microsporogenesis, megasporogenesis. Pollination
and fertilization till the development of mature embryo.

3. Fritillaria tenella and Lilium
martagon
Histrory
The Greek philosopher Aristotle (384-322 B.C.) is the
‘Father of the Study of Natural Sciences’.
Later Theophrastus (370-287 B.C), the ‘Father of Botany’
in third century B.C. referred the pollination of the date
palm. the nature of sexuality of plants was forgotten for
about 2,000 years and his report was considered as useless
Nehemiah Grew who first clearly stated, in 1682, that the
stamens are nothing but the male sex organs of a plant.
In 1694, R. J. Camerarius suggested that the anthers are
the male sex organs of a plant, while the ovaries with the
styles were the female sex organs.
J. G. Kolreuter (1761) fully confirmed the idea of
Camerarius.

4. FLOWER
STRUCTURE

5. Sexual reproduction
takes place with slight
variations in different
groups of plants.
Plants have two
distinct stages in their
lifecycle: the
gametophyte stage
and the sporophyte
stage.

7. MALE
GAMETOPHYTE

8. A. Epidermis
It is the outermost layer of a young anther and undergoes only anticlinal divisions. It is single layered.
Function: It performs the role of protection.
B. Endothecium
Immediately below the epidermis, the cell layers are radially elongated and develop fibrous thickenings bands
which U shaped. These cells are hygroscopic in nature and help in dehiscence of anther and discharge of
pollen. It is generally single layered but some plants it may be multilayered.
C. Middle layer
Usually one to three middle layers are found below the endothecium. The cells are paremchymatous which
present between endothecium and tapetum from middle layer. These cells are ephemeral and degenerate completely
before pollen mother cell undergoes meiosis. (They become crushed at the time of meiotic division in the pollen.)
Function: The middle layers store the food material which is utilized by pollen mother cells.

9. Tapetum
The cells of the innermost parietal layer possess dense protoplasm and the food entering into
the sporogenous cells pass through it. Thus it serves as a nutritive layer for the developing
microspore. The tapetum may be glandular or amoeboid based on the behaviour of the cells
during sporogenesis.
Two types
1-Amoeboid or invasive or periplasmodial 2-Secretory or glandular tapetum

13. 5. Tapetum is associated with the development of pollen grains
because when tapetum is degenerate before microsporogenesis,
the pollen grains produced are steril or abortive.
6. Pollen wall contains proteins derived from the gametophytes
as well as the tapetal cells. These proteins are responsible for
pollen allergy.

14. STRUCTURE OF POLLEN GRAINS
Tube cell, which will eventually become
the pollen tube, and a generative cell, which
contains the male sperm nuclei needed for
fertilization.
There are three main components of a pollen
grain. The inside of the grain is made up
of cytoplasm. This fluid medium houses the
aforementioned living cells, keeping them
moist and alive. The outer shell is made up of
two layers. The inside layer is aptly named
the intine (think interior). It is composed partly
of cellulose, a common component in the cell
walls of plant cells.

15. The tough outer layer is known as the exine (think exterior). This highly
sophisticated and complex outer layer is rich in a compound known
as sporopollenin.
On the surface of the pollen there is a sticky layer known as the pollen
coat or pollen kit, which is a rich source of proteins, lipids, vitamins,
phenolic compounds and minerals for the bees. The extent and chemistry
of pollenkit varies from species to species and the bees prefer pollen rich
in pollen kit.

16. STAGES OF DEVELOPMENT OF MALE GAMETOPHYTE

18. Vegetative cell -
After pollen grains divide into two cells, the vegetative cell increases in size. The cell
organelles increase in number and size. Vegetative cells includes organelles such as
ribosomes, E.R., plastid, dictyosomes, and mitochondria. Nucleus is spherical or
irregular in outline containing chromosomes and one or two nucleoli. In mature stages
nucleus often lacks nucleolus.

19. Generative cell-
(A reproductive cell, especially a cell of an
angiosperm pollen grain that divides to
produce two male gamete nuclei)
Initially the generative cell is attached to intine
of the pollen wall but later on it gets detached
from the pollen wall. It lies free in the
cytoplasm of vegetative cell but there is no
cytoplasmic connection between two cells.
The generative cell cytoplasm contains the
organells Such as mitochondria, ribosomes,
endosplasmic reticulum, microtubule, and
dictyosomes (In the embryo sac, the double
fusion of the generative cells with the egg cell
and the two nuclei of the central cell give rise
to the diploid zygote and the triploid
endosperm, respectively.)

20. Formation of male gametes-
In the anthers of a flower, certain diploid cells undergo meiosis, forming
haploid spores (called microspores—"little spores"). These microspores
divide by mitosis to form two-celled pollen, consisting of a vegetative cell
and a generative cell. Or may be three celled (vegetative + 2 male
gamets) at time of release from the anther. When the pollen grain release
it landed on the stigma, The pollen grains has two cells (vegetative and
generative cell). The generative cell forms two gametes. These are non
motile. In angiosperms the female gametophyte (embryo sac) is situated
at distance from the stigma and to transport the male gamets pollen tube
is form. The pollen tube along with two male gamets grows down through
the style and enters the ovule for the process of fertilization.