Plant Embryology

Department of Botany

Kalindi College

Practical e-resource

B.Sc. Life Science 2nd Year

Dr Divya Verma

PRACTICALS

7. Structure of anther (young and mature), tapetum (amoeboid and secretory)

(Permanent slides).

8. Types of ovules: anatropous, orthotropous, circinotropous, amphitropous or

campylotropous.

9. Female gametophyte: Polygonum (monosporic) type of Embryo sac

Development (Permanent slides/photographs).

10. Ultrastructure or mature egg apparatus cells through electron micrographs.

11. Pollination types and seed dispersal mechanisms (including appendages, aril,

caruncle) (Photographs and specimens).

7. Structure of anther (young and mature), tapetum (amoeboid and secretory)

(Permanent slides).

Comments:

Stamen in a flower consists of two parts, the long narrow stalk like filament and upper broader knob-like

bi-lobed anther.

A normal bithecous or dithecous anther is made up of two anther lobes, which are connected by a strip

of sterile part called connective. Two anther lobes contain four elongated cavities or pollen sacs

(microsporangia) in which pollen grains are produced.

T.S of Young anther reveals the presence of outermost epidermis. The outermost wall layer lying just

below the epidermis is called endothecium. Below the endothecium are 1-3 middle layers of parenchyma

cells. The cells of innermost wall layer are radially elongated, multinucleate and rich in protoplasmic

contents. This layer is called tapetum which forms the nutritive tissue nourishing the developing

microspores.

The tapetal cells provide nourishment to young microspore mother cells either by forming a plasmodium

(amoeboid or invasive type) or through diffusion (parietal or secretory or glandular type).

In glandular or secretory tapetum, cells remain in their sac and later disintegrate and absorbed by

pollen mother cells. It is the most common type of tapetum in angiosperms, where the cells remain in

their original position and later break down progressively.

In amoeboid or invasive or periplasmodial tapetum, cells flows into the sac interior after callose

dissolves and engulfs the separated microspores. This type of tapetum is seen in Alisma, Butomus,

Tradescantia, Typha, etc. where, the tapetal cells fuse among themselves to form a tapetal

periplasmodium. The protoplast of the fused tapetal cells move into the locule, where they surround the

pollen mother cells or the developing pollen grains. This protoplast movement into the locule may take

place during meiotic prophase or may be delayed until the tetrad stage.

Young Pollen sac structure

Anther

T.S Mature Anther (dehisced)

T.S Young Anther

Source:

http://cdn.yourarticlelibrary.com/wpcontent/uploads/2014/02/imagethumb35.png;

http://cdn.yourarticlelibrary.com/wp-content/uploads/2013/10/image37.png

http://slideplayer.com/5030765/16/images/6/Tapetum+type.jpg

http://slideplayer.com/4897864/16/images/9/T.ST.S+of+anther+showing+amoeboid+tapetum.jpg:

http://docsdrive.com/images/ansinet/ijb/2008/fig1-2k8-241-244.jpg

T.S Anther (Amoeboid tapetum)

T.S Anther (Secretory tapetum)

Enlarged view

8. Types of ovules: anatropous, orthotropous, circinotropous, amphitropous

or campylotropous.

Comments:

In angiosperm, ovules basically consist of a nucellus enclosed by two integuments.

Following structures can be observed in the slide of L.S. of ovule:

Funiculus: Ovules are attached to the placenta by a stalk which is known as funiculus. It contains a

vascular bundle running from the placenta to the ovule.

Chalaza: It is the region right beneath the base of the nucellus where the integuments set out.

Integuments: These are collar like structures originating from the base of nuclellus and surrounding it

except the apex.

Micropyle:At the apex a narrow passage, through which a pollen tube reaches the nucleus, is formed

by the integuments called micropyle.

Nucellus: It forms the main part of ovule. It is equivalent to the megasporangium, in which a

megaspore mother cell go through meiosis producing four megaspores, characteristically only one of

which grows into an embryo sac.

Embryo sac: It represents the megagametophyte. It contains mostly four or eight nuclei, structured

into four or seven cells, depending on number of mitotic divisions in the growing embryo sac.

https://doi.org/10.1093/aob/mcr120

http://www.pnas.org/content/108/13/5461/F2.large.jpg

L.S of Orthotropous ovules

Orthotropous Ovule:

The micropyle, chalaza and funicle are in a straight line. This is the most primitive type of ovule.

e.g. Piper, Polygonum, Cycas.

https://doi.org/10.1093/aob/mcr120;

http://dx.doi.org/10.1016/j.bjp.2015.08.006 L.s. of Anatropous ovules

Anatropous Ovule:

The ovule turns at 180⁰ angle. Thus it is inverted ovule. Micropyle lies close to hilum or at side of

hilum.

It is found in 82% of angiosperm families.

Fu: funiculus, ot: outer integument,

it: inner integument, nu: nucellus,

np: polar nuclei; oo:oosphere

L.s. of Circinotropous ovule http://www.scielo.org.mx/img/revistas/rm

biodiv/v81n1/a11f7.jpg

Circinotropous Ovule:

The ovule turns at more than 360⁰ angle, so funicle becomes coiled around the ovule.

e.g. Opuntia (Cactaceae), Plumbaginaceae.

Campylotropous ovule

In the zig-zag micropyle, the part formed by

the outer integument is marked with a green

arrow, the part formed by the inner

integument with a red arrow.

https://doi.org/10.1093/aob/mcr120

https://www.researchgate.net/profile/Maria_Moco/publication/248197831/figure/fig3/AS:298410163884033@1448157935126/Fig-3-Ovule-development-in-Potamogeton-

polygonus-A-B-and-D-H-and-P-iilinoensis-C.png

Campylotropous Ovule:

Ovule is curved more or less at right angle to funicle. Micropylar end bends down slightly e.g. members

of Leguminosae (such as Pisum sativum), Cruciferae (such as Brassica campestris).

9. Female gametophyte: Polygonum (monosporic) type of Embryo sac

Development (Permanent slides/photographs).

http://cdn.yourarticlelibrary.com/wp-content/uploads/2013/10/image32.png

Comments:

Polygonum type angiosperm embryo sac develops

from a single functional chalazal megaspore.

In the coenocytic phase, three successive equal

mitoses produce eight nuclei.

Cellularization follows rapidly, resulting in eight

nuclei and seven cells: three chalazal antipodal cells,

two polar nuclei in a central cell, and a three-celled

micropylar egg apparatus (two synergids, each with

characteristic filiform apparatus, plus an egg cell).

https://embibe-cdn.s3.amazonaws.com/resources/images/embryosac_4.jpg

10. Ultrastructure of mature egg apparatus cells through electron micrographs.

L.S through egg apparatus and polar nuclei (PN). (CC -

central cell, EC - egg cell, N - nucleus, Sy - synergid).

H.J Wilms (1981) Ultrastructure of the developing embryo sac of spinach. Ada Bot. Neerl. Pp. 75-95

https://www.researchgate.net/profile/Bartosz_Plachno/publication/2561008

02/figure/fig3/AS:202763456782344@1425353983061/T-brandenburgicum-

Structure-of-the-ovule-embryo-sac-embryo-and-endosperm-a-c-Images.png

Micropylar pole of Embryosac with Egg apparatus

in T. tenuifolium. Eg - egg cell, S- synergid, It –

integumentary tapetum

10. Electron micrograph of synergids with filiform appendages.

The Egg Apparatus

Comments:

• Typically the egg apparatus is composed of an egg and two synergids.

• As a rule each of the synergids is notched by an indentation resulting in the formation of a prominent

hook. The upper part of the cell is occupied by the so-called "filiform apparatus'‘ which shows a number

of striations converging towards the apex. The nucleus lies in or just below the region of the hook and

the lower part of the cell contains a large vacuole.

• In the egg, on the other hand, the nucleus and most of the cytoplasm lie in the lower part of the cell and

the vacuole in the upper.

• Usually the synergids are ephemeral structures which degenerate and disappear soon after fertilization

or even before it. In some cases, however, one or both of them may persist for a time and show signs of

considerable activity.

11. Pollination types and seed dispersal mechanisms (including appendages,

aril, caruncle) (Photographs and specimens).

Pollination

Self-Pollination/Autogamy Cross-pollination

Xenogamy

(flowers of different plants) Geitonogamy

(different Flowers of same plant)

Abiotic agencies Biotic agencies

Anemophily (wind)

Hydrophily (water)

Entomophily (Insect)

Ornithophily (Birds)

Chiropterophily (Bats)

Pollination is the act of transferring pollen grains from the male anther of a flower to the female

stigma. Plants can be:

Self-pollinating - the plant can fertilize itself

Cross-pollinating - the plant needs a vector (a pollinator or wind or water) to get the pollen to another

flower of the same species.

Anemophily

Anemophily

Anemophilous or wind-pollinated flowers are inconspicuous and not showy.

They are also devoid of scent, nectar, etc. They produce a very large quantity of dusty pollens.

Another adaptation of anemophilous flowers is the branched bushy stigma capable of catching pollens

from air easily as is seen in cereals. Such flowers are often unisexual and occur in bunches.

The anthers are often versatile, swinging freely in air and the pollens are dry, light and smooth-walled.

Eg. Grasses.

Hydrophily

Hydrophily

Certain plants, as those of the families Ceratophyllaceae,

Potamogetonaceae, Hydrocharitaceae, etc., are completely aquatic

so that their pollination is adapted to such conditions. Pollination

takes place completely under water (hypohydrogamous) in

Ceratophyllum while it takes place on the water surface

(epihydrogamous) in the common water weeds Vallisneria,

Hydrilla etc.

The dioecious plant Vallisneria having strap-shaped leaves grow in

the mud at the bottom of stagnant water. The male flowers are

borne low down amongst the radical leaves on short-stalked

spadix inflorescences out of which the individual flowers get de-

tached and float freely in large numbers on the water surface.

These flowers open on the surface and the three perianth leaves

open widely exposing the two stamens vertically. The female

flowers are borne singly on long wiry stalks which grow in such a

manner that the flowers float on the water surface when mature.

As the female flower is some what waxy, it causes a slight

depression in the film of water because of surface tension. This

depression, as well as wind, causes the detached male flowers to

cluster around the floating female flower and, when the anthers

burst, sticky pollens get attached to the stigma. Soon after

pollination, the long stalk of the female flower begins to coil

bringing the female flower again below water level until it reaches

almost the tank base where the fruit matures.

Entomophily

A great majority of the flowers that we see about us today are insect-pollinated.

Insect-pollinated flowers are made attractive to insects in different ways (color, scent, nectar, edible

pollen etc.) and the pollens are sticky with a rough surface so that they may easily stick to insect limbs.

The stigma also is similarly sticky to be able to receive the pollens more easily.

Entomophily

Ornithophily

Bird-pollinated flowers are few in number.

Bird pollinated flowers tend to be large, colourful, often tubular and secrete copious nectar. They also

tend to be unscented.

Tiny birds like the humming-birds and the honey-thrushes feed on the nectar of flowers like Bignonia

capreolata and thereby pollinate them.

Large flowers of Strelitzia (Musaceae) are pollinated by a honey bird called Nectarina afra.

Silk-cotton (Salmalia or Bombax), Erythrina and a few other trees are visited by crows and mynas

when in flower and play part in the pollination.

Ornithophily

Chiropterophily

Chiropteriphily

Bat-pollinated flowers tend to be large and showy, white or light coloured, open at night and have

strong musty odours.

They are often large, bell-shaped and have a ball of stamens.

Flowers are typically borne away from the trunk or other obstructions.

Bauhinia megalandra of Java, Eperua falcata (Leguminosae) and a few other trees like Adansonia

dictata and Kigelia africana are known to be visited and pollinated by bats.

Seeds are mature and fertilized ovule. Seed formation is the characteristics of spermatophytes.

Angiospermic seeds contain three genetically different components:

• Embryo (formed by fusion of egg and male sperm)

• Endosperm (formed by fusion of polar nuclei and male sperm)

• Seed coat (formed from integument)

Seed dispersal is the movement or transport of seed saway from the parent plant. Plants have very

limited mobility and consequently rely upon a variety of dispersal vectors to transport their propagules,

including both abiotic and biotic vectors.

The means by which seeds are dispersed depend on a seed's structure, composition, and size.

Seed dispersal mechanisms

By wind

(Anemochory)

By Animals

(Zoochory)

Seed Dispersal Mechanism

By water

(Hydrochory)

Mechanical

(Autochory)

Wind dispersal/Anemochory

1. For easy dispersal by wind seeds have to be light so that their buoyancy may enable them to float on air

over long distances.

2. Plants that produce wind blown seeds eg. Dandelion often produce lots of seeds to ensure that some of

the seeds are blown to areas where the seeds can germinate.

3. Seeds specially adapted for wind dispersal are characterised by the following:

• Very small, dry and dusty seeds eg. Orchids seeds are carried by wind like pollens.

• Seeds of Cinchona are also extremely small and winged.

• Certain seeds are provided with appendages which act like parachutes in helping them to float in air

(parachute mechanism).

Coma is a tuft of hair developed as a crown on the seeds of Calotropis, Holarrhena, Alstonia (two tufts)

and most plants of Apocynaceae and Asclepiadaceae.

Hairy outgrowths on the testa completely cover cotton seeds.

Seeds of Moringa oleifera, Oroxylum indicum, Lagerstroemia speciosa, Swietenia mahogoni,

Cinchona, etc., are provided with wings developed from the testa.

Wind dispersal/Anemochory

Calotropis Alstonia

Moringa Lagerstroemia

Wind dispersal/Anemochory

Dandelion

Wind dispersal of dandelion seeds

Water dispersal/Hydrochory

1. Seeds dispersed by water are provided with a coat

which is waterproof, salt-resistant and buoyant.

2. Seeds of many aquatic plants like water-lily, Alisma,

Sagittaria, etc., are very light and waterproof so that they

can float easily. Many of these seeds are provided with

spongy arils rendering them more buoyant.

3. Seeds dispersed by water are contained in light and

buoyant fruit, giving them the ability to float Eg.

Coconuts. Similarly, willow and silver birches produce

lightweight fruit that can float on water.

Mechanical/Autochory

1. All dehiscent fruits scatter the seeds when they burst. This dehiscence is accompanied by the

expression of great force in many fruits so that seeds are jerked a considerable distance away from the

mother plant. Such fruits are called explosive fruits.

2. Legumes of the mountain climber Bauhinia vahlii similarly explode with loud noise scattering the

seeds yards away in all directions. The ripe pods peas, beans etc., suddenly twist on bursting and thus

scatter the seeds.

3. Ripe fruits of Impatiens balsamina (balsam) explode suddenly when touched. The valves are bent and

the seeds are jerked off forcibly.

4. In certain fruits the seeds are discharged through small openings on the fruits. The outlets are so narrow

that only a few seeds can escape at a time. In Argemoru mexicana and the poppies of Papaveraceae, after

the apertures are opened by porous dehiscence, as the capsule swings in air, the minute seeds are

dispersed through the pores.

Poppies

Animal dispersal/Zoochory

1. Animals can disperse seeds by excreting or burying them; some have structures, such as hooks, that

attach themselves to animals' fur.

2. Seeds of many plants are provided with hooks, spines, barbs or stiff hairs so that if an animal grazes or

brushes against them, these stick to the animal’s body or clothing.

3.Many seeds, as those of Aegle marmelos, Plumbago, Mistletoe, etc., are sticky and are thereby

benefited.

4. Humans also play a role as dispersers by moving fruit to new places and discarding the inedible

portions containing the seeds.

5. In some seeds, post-fertilization developments in seed coats leads to formation of appendages like aril,

caruncle, elaiosomes etc which help in their dispersal

Acacia melanoxylon seeds are almost encircled

by a large pink, pinkish-red or dark red folded

fleshy structure (aril).

Red aril in Myristica fragrans

(Myristicaсеаe) seed

Aril

An aril, also called an arillus, is a specialized outgrowth from a seed that partly or completely covers

the seed. An aril grows from the attachment point of the seed to the ovary (from the funiculus or hilum).

It is regarded ad third integument. Arils are often edible enticements, encouraging transport by animals

and thereby assisting in seed dispersal.

Caruncle Also known as Strophiole. It is a fleshy, whitish beak like structure arises due to proliferation of cells at

the tip of outer integuments is called as caruncle eg. Castor (Ricinus communis). This structure has the

ecological function of promoting seed dispersal by ants (myrmecochory).

Castor bean (Ricinus): small

water-absorbing appendage

(caruncle) at the end of each seed

Elaiosomes

Elaiosomes ("oilbody") are fleshy structures that are attached to the seeds of many plant species. The

elaiosome is rich in lipids and proteins, and may be variously shaped. Many plants have elaiosomes that

attract ants, which take the seed to their nest and feed the elaiosome to their larvae. After the larvae have

consumed the elaiosome, the ants take the seed to their waste disposal area, which is rich in nutrients

from the ant frass and dead bodies, where the seeds germinate.

This type of seed dispersal is termed myrmecochory from the Greek "ant" (myrmex) and "dispersal"

(kore). This is mutualistic relationship, as the plant benefits because its seeds are dispersed to favorable

germination sites, and also because it is planted (carried underground) by the ants. Elaiosomes mostly

develop from seed tissues (chalaza, funiculus, hilum, raphe) and serve the main function, i.e. attracting

ants.