This presentation offers the basic idea about the reproductive biology of angiosperms in plant kingdom.

1. 

2.  Reproductive Biology is the branch of sciences deals with the different
aspects of the reproductive issues of organisms in general and sexual
reproduction in particular in the light of morphological, cytological &
embryological attributes. Sexual reproduction involves a series of changes
like preparation of sex organs(Gonads), formation of haploid gametes,
union of gametes as fertilization, post zygotic changes and post embryonic
changes making passage to give offspring with variation. In plants, it is
mediated by alternation of generations via microsporogenesis,
megasporogenesis, pollination, fertilization and development of mature
embryo. This fundamental process of reproduction is DNA replication. In
other words, if an organism wants to continue its species, then they need to
transfer their traits to the next generation by DNA (genetic information)
copying which occurs during the process of reproduction. We know
asexually reproducing organisms copy their DNA and divide themselves
into new cells which are their clones.

3.  Since the process of replication is not completely reliable, there are
chances of variation, but they are quite limited. Organisms need to adapt
themselves to the changing environment; the creation of variants needs to
be hastened for this reason. This will only happen when there is a union of
two different DNAs. This highlights the significance of sexual
reproduction in organisms. If two reproducing cells simply join, the
chromosome number in the new organism will be doubled. But this cannot
happen because the number of chromosomes in each cell of every organism
is fixed – the same holds good for the reproducing cell. Thus, the
reproducing cells from both parents reduce their chromosome number into
the half before fusion and are called gametes (germ cells). In simple
organisms, the size and shape of gametes are almost the same. But in
higher organisms, a male gamete is small and mobile while female gamete
is large, immobile and they store food for the fetus. The gametes are
produced in a specialized system called the reproductive system.

5.  The following basic steps are involved----
 The transformation of the vegetative phase into reproductive phase by the
induction of flower through a series of changes leading to the development
of flower,
 Microsporogenesis in stamen to form haploid poille4n grains-the 1st cell of
the male gametophyte and the megasporogenesis to form the megaspore as
the 1st cell of the female gametophyte,
 Pollination: Either by self pollination( autogamy or Geitonogamy) or cross
pollination, Pollen reaches the stigma of a flower.
 Germination: Pollen germinates and forms a pollen tube that reaches the
ovary, and the haploid male gamete is released into the embryo sac by
different embryological processes.
 The ovule by this time get ready for the development of embryo sac
comprising of egg, secondary apparatus & others
 Fusion: Male gamete fuses with female gamete and forms zygote.
 Post-zygotic changes lead to the formation of embryo, seed formation takes
place, baby plants derived---alternation of generation comes to an end.

7.  As we enter the 21st year of the journal Sexual Plant Reproduction, it seems
both fitting and appropriate to consider the genesis both of this journal and its
parent organization, the International Association for Sexual Plant
Reproduction Research (IASPRR)—particularly through its much longer
history of plant sexual reproduction congresses, informal interactions and this
area of scientific pursuit as it is transformed in the modern era. The science of
sexual plant reproduction has a long history that reaches beyond the 315 years
interval since Camerarius uncovered the sexuality of plants (Žárský and Tupý
1995), passing 150 years of neglect before the discovery of gametes, and then a
great period of exploration in the 1800s concluding with the discovery of
double fertilization in 1898 by Nawashin.From Theophrastus,
Herodotus,Leewenhoek, Grew, Camerrius,Kolreuter different plant scientists
have enriched this domain. Giovanni Battita Amici(1824) made significant
contribution by discovering the pollen tube while studying the stigma of
Portulaca oleracea.He splitted open the pollen tube and entered the tissue of
stigma.

8.  The formation of embryo in plants as the onset of life was a very crucial
question and the dilemma was about the origin of the embryo. William
Hofmeister first demonstrated that in every case, the embryo originated
from pre-existing cell in the embryo sac and not from the pollen tube on
the basis of the observations of 38 species belonging to 19 genera of
angiosperms. This observations ended a rigid controversy between
Schliden and his opponents. The experimental research along with its
proper documentation of the origin of embryo and its nature of origin
become crystal clear to the biologists after this epoch making research and
this made a new avenue of the understanding about the sexual reproduction
of the higher plants. Hofmeister is widely credited with discovery of
alternation of generations as a general principle in plant life. His proposal
that alternation between a spore-bearing generation (sporophyte) and a
gamete-bearing generation (gametophyte) constituted a unifying theory of
plant evolution that was published in 1851.

9.  Eduard Strasburger, director of the Botany Institute and the Botanical
Garden at the University of Bonn from 1881 to 1912, was one of the most
admirable scientists in the field of plant biology, not just as the founder of
modern plant cell biology but in addition as an excellent teacher who
strongly believed in "education through science." He contributed to plant
cell biology by discovering the discrete stages of karyokinesis and
cytokinesis in algae and higher plants, describing cytoplasmic streaming in
different systems, and reporting on the growth of the pollen tube into the
embryo sac and guidance of the tube by synergides. Strasburger raised
many problems which are hot spots in recent plant cell biology, e.g.,
structure and function of the Plasmodesmata in relation to phloem loading
(Strasburger cells) and signaling, mechanisms of cell plate formation,
vesicle trafficking as a basis for most important developmental processes,
and signaling related to fertilization. Demonstrated the wide spread
occurrence of the binucleate condition of pollen grains and worked out the
organisation of the embryo sac of Polygonum divaricutum.

10.  He Also pointed out that the nucellus lying close to the apex of the embryo
sac become richly protoplasmic and divide to form small groups of cells
which project into the cavity of the embryo sac and grow into embryo on
the basis of the ontogeny study of citrus aurantium.
 Discovered syngamy, development of embryo sac from megaspore mother
cells and pointed out modification of synergids in the process of
fertilisation.
 Strasburger was the author of the important book Ueber Zellbildung und
Zelltheilung (1875), and an influential Lehrbuch der Botanik fuer
Hochschulen (1894, 196729; Textbook of Botany, 1898, 19657). Under his
direction, the botanical institute became a world center for research in
botany and especially in the newly emerging science of cell biology.
Strasburger's early research dealt with the embryology of liverworts, ferns,
and conifers. He recognized the homology of the archegonia of the fern
with the embryo sac of conifers.

11.  Double fertilization is a characteristic feature of angiosperms. Syngamy
causes the formation of embryo, where the male and female gametes fuse.
Along with that the secondary polar nuclei fuse with male gamete to form
triploid endosperm. It provides the function of nourishment.
 Navashin's embryological research led him to the important discovery in
1898 of double fertilization in angiosperms. Observing fertilization in the
Turk's- cap lily (Lilium martagon) and Fritillaria tenella, he was the first to
note that this process involves not one but two sperm, which form in the
pollen tube. In a study of Lilium martagon and Frititlaria tenella. showed
that in angiosperm both male gamete are concerned in fertilization, on
fusing with the egg (syngamy) and the other with the two polar nuclei
(triple fusion).In the study of Lilium sp, he observed that male gamete on
fusing with egg as syngamy and other male gamete with two polar nuclei
as triple fusion. Double fertilization as universal occurrence of
angiosperms. Explored a new breeze in the developmental biology of
angiosperms.

12.  Panchanan Maheswari was an eminent Indian botanist and he was known for
his discovery in the technique of test-tube fertilization of angiosperms.
- Test tube fertilization or in vitro fertilization is a type of process involving
fertilization where the egg is fused with the sperm outside i.e. in a glass or test
tube. The whole process is monitored as the fertilized egg is developed into an
embryo. Cultivation of plant tissue and other organs on an artificial media in a
test tube is in vitro technique. P. Maheshwari who served as Professor and
Head of the Department of Botany, University of Delhi from 1950 to 1966
built a flourishing school of embryology which became internationally
recognized. His colleagues and students have contributed significantly to all
areas of embryology through integrative approaches. In memory of his birth
centenary year, we have prepared this article that summarizes the work done by
his students and traces the phenomenal advances made in some areas in the
post-Maheshwari era. Father of Indian Embryology, famous for test tube
fertilization of angiosperms by tissue culture methods. Wrote an important
book on “Embryology of Angiosperms” along with a number of contributions
in applied and Experimental plant embryology. The valuable contributions are
available with the genera like Paeonia,Trapa, Butomus,Peganum,Parasssia etc
& families like Crassulaceae, Liliaceae,Loranthaceae,Lemnaceae,Cyperaceae
etc.

13.  During the 20th century, significant advances have been made in
developmental and comparative embryology and its role in taxonomic
considerations.Howerver, the causes of the variations in spindle
organization during microsporogenesis, pollen structure in Cyperaceae and
Epacridaceae, pollen bud development in some members of Rubiaceae,
pollen embryo sac in experimental embryology are some of the works .
◦ W.A.Jensen
 Orchid is the most important epiphytes and it is worthy to be praised by the
beauty lovers due to its showy & bizarrely shaped structure.It belongs to
the most developed family, Orchidaceae and it encompasses 6-11% of the
seed plants. Starts in the Orchid embryology. He also contributed a lot in
Capsella embryogenesis, the central cell plays an important role in the
double fertilisation.The relationship to the central cell to the other cells of
the mature megagemetophyte and its possible role in embryogenesis was
discussed by W.A .Jensen in the paper entitled”Capsella Embryogenesis:
The central cell”.

14.  Heslop Harrison was an eminent English professor of botany who was
based in Newcastle in the middle years of the twentieth century and who
sired a mini-dynasty of other eminent biologists. He was a Fellow of the
Royal Society as was one of his sons; a very unusual occurrence.
Genetically work on plants on wild roses & Willows, Rose hybrid & Salix
hybrid, Light effect on the pupae of Butterfly.
 A number of Indian scientists like Swamy, Maheswari, johri,Vasil, shivana
& others have contributed a lot to enrich this subject.
 If you have the passion, you can a do a lot by your research & innovative
mind.

16.  1. Google for images,
 2. Different websites to exp0lore the idea,
 3. An Introduction to embryology- P. Maheswari
 4.Plant anatomy 7 embryology- Pandey & Chakdah
 5.A textbook of Botany- B.P. Pandey
 6.The embryology of angiosperms- S.S. Bhojwani,
 7. The Embryology of angiosperms- Bhojwani, Bhatnagar & Dantu
 Disclaimer: This presentation has been made to enrich open source of
knowledge without any financial pleasure.