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Embryology and taxonomy

The document explores plant embryology, detailing processes from microsporogenesis to embryo development, emphasizing its significance in taxonomy. It discusses historical milestones in the field, general terms, embryological characters, and the role of palynology in classification. Key findings include the stable nature of embryological traits aiding taxonomy and the classification of angiosperms based on embryological features.

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EMBRYOLOGY AND TAXONOMY KHASLA COLLEGE AMRITSAR NAVNEET KAUR P.G. DEPARTMENT OF BOTANY M.SC. BOTANY SEM 3 19712042 GUIDE- DR. MANINDER KAUR
CONTENT Introduction History General embryological terms Diagnostic embryological characters Primitive and advance embryological characters Role of embryology in taxonomy Role of palynology in taxonomy Summary References
INTRODUCTION  Plant embryology deals with the study of all events starting from microsporogenesis, megasporogenesis, pollination, fertilization till the development of mature embryo.  The seed is the structure in which the embryo is enclosed.  Palynology is the study of pollen and pollen spore wall.  Taxonomy is the branch of science concerned with the classification, especially of organisms.
HISTORY  Sexuality in angiosperms has been known since third century B.C. However, sexual cells were first observed by Leeuwenhoek (1677).  Grew (1682), highlighted the fact that stamens are the male sex organs of the plant and pollen grains influence the ovary to produce fruit  Rudolph Jakob Camerarius (1694), established sexuality in some plants, as Zea mays.
 Joesph Gottlieb Kolretuter (1762) demonstrated that the seeds can be produced by artificial pollination. He also produced hybrids.  Giovami Battitia Amici (1824-1842), he observed that pollen grains burst into a tube. He also observed the true relation between pollen tube and the embryo.  Matthias Jakob Schleiden (1837), confirmed Amici’s work.  Hofmeister (1849), also confirmed Amici’s work. He also studied tetrads during microsporogenesis, about female gametophyte and cellular endosperm.
 Hanstein (1870), was the first to follow the sequence of early division in the development of embryo.  Edward Strasburger (1878, 1879, 1884), traced the development of adventive embryo from nucellus and development of female gametophyte.  A significant research was the discovery of Syngamy in Monotropa.  Nawaschin (1898), discovered double fertilization.  1900, marked the new era in angiosperm embryology.
GENERAL BASIC TERMS Sporogenesis Gametogenesis Pollination Fertilization Double fertilization Endosperm Embryogenesis
SPOROGENESIS Sporogenesis is the formation of haploid spores. It is of two types:- • Microsporogenesis • Megasporogenesis
Microsporogenesis It is the process of development of development of haploid microspores from diploid microspore mother cells in the microsporangium. Figure – T.S. of anther and development of pollen grains Source – Goyal, J.P., Saini, A. (2016). Angiosperms. Structure, Development and Reproduction. Trueman’s publication, Jalandhar - Punjab
Megasporogenesis The process of development of haploid megaspores from the diploid megaspore mother cells in the nucellus is called megasporogenesis. Figure – various stages of megasporogenesis Source – Goyal, J.P., Saini, A. (2016). Angiosperms. Structure, Development and Reproduction. Trueman’s publication, Jalandhar - Punjab
GAMETOGENESIS The process of development of gametophytes from haploid spores is called gametogenesis. • Microgametogenesis • Megagametogenesis It is of two types:-
Microgametogenesis It is the process of development of male gametophyte from microspores (pollen grains). Figure – Process of microgametogenesis Source – Goyal, J.P., Saini, A. (2016). Angiosperms. Structure, Development and Reproduction. Trueman’s publication, Jalandhar - Punjab
Megagametogenesis It is the process of development of female gametophyte from the haploid megaspore. Figure – various stages of Megagametogenesis Source – www.topper.com/projects.ncsu.edu
POLLINATION The transfer of pollen grains from the anther to the stigma whether of the same flower or of different flower is called pollination. It is of two types:- Self pollination Cross pollination
Self pollination It is of two types:- Autogamy Geitonogamy It is the transfer of pollen grains from the anther of a flower to the stigma of either the same or different but genetically similar flower. Figure – Self pollination Source - https://www.britannica.com/science/self-pollination
Cross pollination It is the transfer of pollen grains from the anther of one flower to the stigma of a genetically different flower of another plant of the same species. Figure – Cross pollination Source – https://www.qsstudy.com/biology/significance-of-cross- pollination
FERTILIZATION The process of fusion of male gamete with the female gamete is called fertilization. Figure – Process of fertilization Source - https://www.topperlearning.com/answer/how-the- process-of-fertilization-takes-place-in-plants-draw
DOUBLE FERTILIZATION Figure – Process of double fertilization Source - https://www.qsstudy.com/biology/double-fertilization- definition-advantages The fusion of two male gametes to two different nuclei of the same female gametophyte in order to produce two different structures (one is zygote and other is primary endosperm nucleus) is called double fertilization.
ENDOSPERM  Endosperm is the food laden tissue triploid (3n) tissue formed as a result of triple fusion of double fertilization and is meant for nourishing the embryo in seed plants.  In gymnosperms, it is haploid, represents the female gametophyte and is formed before fertilization.  These are of following types:-  Nuclear endosperm  Cellular endosperm  Helobial endosperm  Ruminate endosperm Figure – Various types of endosperm Source - http://www.brainkart.com/article/Post-Fertilization- structure-and-events_38204/
EMBRYOGENESIS  Study of structure and development of embryo from the zygote is called embryogenesis.  In angiosperms, the development of embryo is meroblastic.  Each division of embryo development is followed by wall formation.  Six types of embryos have been recognized:-  Piperad type  Crucifer type  Asterad type  Caryophyllad type  Solanad type  Chenopodiad type
Dicot embryo A typical dicot embryo (crucifer type) consist of an embryo axis with two lateral cotyledons. Plumule is apical, radicle is formed by embryo cell and suspensor is formed by basal cell alone. Proembryo is four celled and inverted T-shaped. The cotyledons developed from two opposite cells of four celled epibasal tier of embryo. Terminal cell produces embryo except the radicle Figure – Developmental stages of dicot embryo and mature dicot embryo Source – Goyal, J.P., Saini, A. (2016). Angiosperms. Structure, Development and Reproduction. Trueman’s publication, Jalandhar - Punjab
Monocot embryo A monocot embryo consist of only one cotyledon, which is terminal in position. Plumule is lateral. Suspensor is formed by both basal and terminal cell and radical is formed by one of the cells of the suspensor. Proembryo is three celled and linear. The number of cells used in the formation of cotyledons are 4, 3 or 2. Terminal cell forms the whole embryo. Figure – Development of monocot embryo and mature monocot embryo Source - https://kullabs.com/class- 12/biology/developmental-biology/fertilization-and- embryogenesis
DIAGNOSTIC EMBRYOLOGICAL CHARACTERS Anther Quadripartition of the microspore mother cell Pollen grain Development and structure of ovule Origin and extent of the sporogenous tissue in the ovule Megasporogenesis and development of embryo Form and organization of the mature embryo sac
Parthenogenesis Apogamy Adventive embryony Polyembryony Fertilization Endosperm Embryo Seed coat Special features
Figure – The process of sexual reproduction and forms of parthenogenesis Source - https://www.britannica.com/science/parthenogenesis
Figure – Polyembryony in Ulmus glabra Source - Bhojwani, S.S. and Bhatnagar, S.P. (1975). The Embryology of Angiosperms. Vikas Publishing House Pvt. Ltd., Delhi. Figure – Citrus ovule in section showing normal and adventive embryo Source - https://www.toppr.com/en-at/ask/question/in- a-type-of-apomixis-known-as-adventive-embryony- embryos-developdirectly-from-the/
PRIMITIVE AND ADVANCE EMBRYOLOGICAL CHARACTERS Primitive embryological characters  A thick anther wall.  Widespread endothecial thickenings.  Several middle layers.  Secretory (glandular) tapetum. Advance embryological characters  A thin anther wall.  Fibrous thickenings limited mostly to endothecium.  Ephemeral middle layers.  Amoeboid (plasmodial, invasive, intrusive) tapetum.
Figure – structure of anther and its T.S. Source - https://www.toppr.com/content/concept/stamens-the- male-reproductive-structures-of-a-flower-255342/ Figure – types of tapetum Source - http://kalindi.du.ac.in/uploads/2017- 18%20Year/Odd%20Sem/Botany/Plant%20Anatomy%20and %20Embryology.pdf
Primitive embryological characters  Successive cytokinesis in pollen mother cell after meiosis.  Two-celled pollen grain.  Anatropous, bitegmic, crassinucellate ovule.  Micropyle formed by both integuments. Massive parietal tissue including nucellar cap formed by division in apical cells of nucellar epidermis. Advance embryological characters  Simultaneous cytokinesis by furrowing in pollen mother cells after meiosis.  Three-celled pollen grain.  Anatropous, unitegmic, tenuinucellate ovule.  Micropyle narrow and short. The inner epidermis of integument differentiates as endothelium.
Figure – Bicellular and tricellular pollens Source - https://www2.le.ac.uk/departments/genetics/people/twell/lab/images/pollis.gif
Figure – structure of anatropous ovule Source - https://qforquestions.com/describe- the-structure-and-various-forms-of-ovule/ Figure – Tenuinucellate and Crassinucellate ovule Source - http://sweetgum.nybg.org/science/glossary/glossary- details/?irn=3245
Primitive embryological characters  Monosporic polygonum type of embryo sac, Chalazogamy.  Nuclear type of endosperm, sometimes ruminate.  Typical dicotyledonous embryo with a conspicuous suspensor. Advance embryological characters  Monosporic, bisporic and tetrasporic embryo sac. Synergids sometimes absent. Antipodal nuclei may or may not organize into cells and they are ephemeral.  Endosperm is of cellular type.  Embryo with few celled suspensor, sometimes suspensor haustoria conspicuous
Figure – Polygonum type of embryo sac Source – Goyal, J.P., Saini, A. (2016). Angiosperms. Structure, Development and Reproduction. Trueman’s publication, Jalandhar - Punjab Figure –Nuclear and cellular endosperm Source - http://www.brainkart.com/article/Post-Fertilization- structure-and-events_38204/
Figure – Different types of embryo sac Source – Goyal, J.P., Saini, A. (2016). Angiosperms. Structure, Development and Reproduction. Trueman’s publication, Jalandhar - Punjab
Primitive embryological characters  Seed albuminous, sometimes perispermous.  Seed coat thick, formed by both testa and tegmen. Advance embryological characters  Seed exalbuminous, perisperm usually absent.  Seed coat exotestal.  Chalazal, micropylar or both chalazal and micropylar haustoria develop, sometimes the haustoria invade the placenta and even pedicel.
Figure – L.S. of Albuminous seed (Castor) Source - https://www.topperlearning.com/answer/a- draw-a-labelled-longitudinal-view-of-an- albuminous-seed-b-how-are-seeds- advantageous-to-flowering- plants/m14xvm955 Figure – Types of seeds Source – Goyal, J.P., Saini, A. (2016). Angiosperms. Structure, Development and Reproduction. Trueman’s publication, Jalandhar - Punjab
ROLE OF EMBRYOLOGY IN TAXONOMY  The role of embryology in solving taxonomic problems was first brought into prominence by a German embryologist, Schnarf in 1931.  Embryological characters being less prone to adaptive stress, are relatively stable and have acquired great significance in plant taxonomy.  Thus, embryological evidences have been used in solving taxonomical problems at almost all levels, and have helped resolve the doubtful systematic position of several taxa.  The delimitation of Angiosperms in the first instance has been largely based on embryological characters. They are characterized by enclosed ovules that are mostly anatropous, polygonum type of embryo sac, double fertilization and triple fusion and post fertilization development of polyploid endosperm.
 The further primary classification of the subdivision Angiospermae into two classes namely, Monocotyledonae and Dicotyledonae is largely based on the characteristics of embryo.  Some orders , families and genera especially marked out by their embryological features of taxonomic importance are:- Above the family level – There are few orders of Angiosperms, the members of which are morphologically well defined and also exhibit a set of uniform embryological characters.
• Caryophyllales • Polygonales and Plumbagoginales • Lecythidales • Ericales • Gentianales • Orchidales A few examples are –
Few examples of some important families are – • Onagraceae • Empetraceae • Loranthaceae • Tropaeolaceae • Garryaceae • Cyperaceae • Podostemaceae At or below family level -
Figure – Embryo sac development in Oenothera acaulis Source - Bhojwani, S.S. and Bhatnagar, S.P. (1975). The Embryology of Angiosperms. Vikas Publishing House Pvt. Ltd., Delhi. Figure – Pollen development in Cyperus Source - Bhojwani, S.S. and Bhatnagar, S.P. (1975). The Embryology of Angiosperms. Vikas Publishing House Pvt. Ltd., Delhi.
Few examples of some important genera are – • Paeonia • Butomus • Exocarpus • Trapa • Pentaphragma • Peganum • Parnassia
Figure – Stages in the embryology of Exocarpus sparteus Source - Bhojwani, S.S. and Bhatnagar, S.P. (1975). The Embryology of Angiosperms. Vikas Publishing House Pvt. Ltd., Delhi.
ROLE OF PALYNOLOGY IN TAXONOMY  Palynology is the study of pollen and spore wall.  It has made significant contributions to taxonomy.  Most extensive studies in this area have been done in the family Asteraceae.  Pollen grains may be vesiculate; saccate or non-saccate, fenestrate or non- fenestrate, colpate or porate.  According to number (one to many), position (proximal, distal, zonal or global), and character of aperture (colpate, porate and inaperturate), pollens are of different types.
Pollen characters considered of taxonomic importance are-  Pollen unit type  Pollen grain polarity  Pollen grain shape  Pollen grain symmetry  Pollen grains nuclear state  Pollen wall architecture  Exine stratification  Exine structure  Exine sculpture
 Aperture type  Aperture number  Aperture position  Aperture shape  Aperture structure On the basis of pollen morphology all angiosperm families are divided into two groups :- 1. Eurypalynous 2. Stenopalynous
1. Eurypalynous -  With respect to the character of apertures and exine sculpturing, there are different pollen types within the family.  In Asteraceae, which is an example of this type, most genera have three zonocolpate pollen.  The various groups are distinguished by the pattern of exine sculpturing, being spinose, granulose, undulate or lophate.
2. Stenopalynous -  With respect to character of apertures and exine sculpturing, a single morphological pollen type occurs throughout the family.  The Brassicaceae are an example of this category.  This family is characterized by having three zonocolpate sporomorphs and exine surface representing a reticulate ornamentation.  In this family various taxa are noticeable by nature of reticulation, being either well developed or faint, heterobrochate or homobrochate.
SUMMARY  Embryology is the study of microsporogenesis, megasporogenesis, gametophyte development, fertilization, development of endosperm, embryo, etc.  Embryological characters being less prone to adaptive stress are relatively stable and have acquired great significance in plant taxonomy and have been used to resolve the doubtful systematic position of several taxa.  Angiosperms are universally divided into Monocotyledons and Dicotyledons and this primary classification is based on a major embryological character i.e., the number of cotyledons.  Palynology is also been recognized as a discipline that has made significant contributions to taxonomy.
REFERENCES  Bhojwani, S.S. and Bhatnagar, S.P. (1975). The Embryology of Angiosperms. Vikas Publishing House Pvt. Ltd., Delhi.  Maheshwari, P. (1950). An Introduction to the Embryology of Angiosperms. Tata McGraw Hill Publishing Company Ltd. Bombay – New Delhi.  Kumaresan, A. (2010). Developmental Botany and Experimental embryology. Saras Publication, Gujarat.  Pandey, S.N. and Chadha, A. (2009). Plant Anatomy and Embryology. Vikas Publishing House Pvt. Ltd., Delhi.
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