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M. Sc. BOTANY
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Paper-V
PLANT DEVELOPMENT AND
REPRODUCTION
Block-I
0
M.P. BHOJ (OPEN)
UNIVERSITY
Paper- V
Block – I
Unit – 1
Edited by –
Written by-
Dr. Renu mishra
Head, Dept. of Botany
and Microbiology
Sri Sathya Sai College,
Bhopal(M.P.).
Dr. Smriti Chitnis
Asstt. Prof. of Botany
Holkar Science College,
Indore (M.P.)
1
UNIT-1
Structure
1.0
Introduction
1.1
Objectives
1.2
Plant development
1.2.1 Features of Plant development
1.2.2 Difference between animal and plant development.
1.3 Seed germination1.3.1 Parts of seed
1.3.2 Food storage in the seeds.
1.3.3 Germination of seed
1.3.4 Conditions necessary for germination
1.3.5 Germination process
1.3.6 Nucleic acids
1.3.7 Hormonal control
1.3.8 Gene expression
1.4 Tropisms.
1.5 Use of mutants.
1.6 Lets sum up
1.7 Check your progress.
1.8
Activities
1.9 References
2
1.0
INTRODUCTION
A plant is a nature’s highly efficient device, which very preciously uses all its
resources to develop into a complete entity. A plant starts its life in the form of a small
seed, which contains a very small embryo along with a little amount of stored food.
When this seed gets proper external conditions, it starts imbibing water, which
dilutes the otherwise concentrated cytoplasm of seed cells. These cells become active and
start production of active enzymes, which further take part in metabolic activities.
Increased rate of metabolism, leads to increase in cell mass and there by cell and nuclear
inclusions. Many other external and internal factors together activate the cells to be
meristematic. These factors include nucleic acids, available food stuff, hormones etc
The growth in plants is localized to the meristems. These meristems together form
the second level of structural units the metamers. The repetitive occurrence of these
metamers forms the modules. These modules form the organs like shoot, root & leaf.
The small developing embryo breakes it’s covering, the seed coat, and comes out
i.e. germinates. When it receives proper light, temperature and air, it starts differentiating
into various cells. Growth hormones influence all the development processes. They
influence the plant at cellular level, organellar level and even at the level of whole plant.
They are -actually chemical messengers, organic in nature, synthesized in response to
some environmental stimulus in one part of the plant and translocated to another part of
the plant where it has a controlling or regulatory effect.
These hormones also regulate the movement of plants in response to external
factors.
3
In this unit, we shall try to understand the development of a new plant, from a tiny
seed. How does this seed transform into a new plant, and what are the factors which
affect the germination and differentiation?
1.1 OBJECTIVES
The main aim of this unit is to study about* Pattern of plant growth and development.
* Structure of seed and its stored food.
* Utilization of stored food in the seed during germination.
* Internal factors responsible for differentiation.
* Movements of plants in response to external factors.
1.2 PLANT DEVELOPMENT
1.2.1 Features of plant development
All the living beings have a common feature of growth. It can be defined
as an irreversible and permanent increase in mass, weight, volume of cell, organ or
organism. Growth is a common word used to designate any change in an organism. But,
it should not be confused with the development. Development is an ordered change or
progress towards a more complex state. It is also an irreversible process that means a
differentiated organ can not become an undifferentiated one.
In unicellular and some other lower forms of plants, all the cells of the body
divide, hence the growth is diffused. But in higher plants, growth is restricted to definite
regions of the body called meristems. The plant body shows two types of growth1. Determinate growth - When a structure grows to a certain size and then
stops, ultimately falls off after senescence eg. Leaves, flowers & fruits.
4
2. Indeterminate growth- when a structure continues to grow for an indefinite
time. eg root & shoot.
The growth and development of the plant is ultimately the growth and
development of the plant cell. So, we can express the development of the plant at
following levels1. Cellular levelThe cells enlarge, elongate & then undergo karyokinensis & then cytokinensis.
These cells differentiate to form various tissues & tissue systems.
2. Organ level The single celled zygote undergoes predetermined divisions to form a wellorganized embryo. This embryo develops to form a seed, which in turn, develops into a
seedling which after full maturation forms root, shoot, leaf, flower & fruits. The site of
the formation of these organs & the time of the formation is preset in the plant. It also
forms special organs like tubers, rhizomes, bulbs, corns, bulbils etc. This level also
decides and forms abscission layers in ripen leaves and fruits.
At this level, movements of organs, either environmentally controlled or Nastic
movement are also included.
3. Whole Plant level At this level, plant’s overall form, in terms of polarity, symmetry is controlled.
During the plant’s life cycle, certain morphological and genetical events take
place. They are in correlation with time. Germination always takes place at a season
favorable for the growth. The onset of flowering is again a time, photoperiod and
temperature influenced phenomenon. Similarly, dormancy of germinating buds, seed and
other vegetative parts is again a way to avoid particular time during the season.
5
So, we can say that all primary tissues of a plant are developed by the activity of
embryonic cells. Some of the embryonic cells at embryonic root and embryonic shoot
become meristematic. They are apical in position and by their activity, root and shoot
apices are formed. Here, other types of meristems as marginal, intercalary, plate, rib are
formed; all of them contribute to the longitudinal and latitudinal development of the
plant.
An important aspect of apical meristem is their repetitive activity. They divide at
regular intervals to form group of cells as leaf primordium in stem apex & root primordia
in root apex. The time interval between the two successive leaf primordia is 3-4 days. At
the higher level of the whole plant, there are periods of meristems activity and inactivity.
Thus, the higher the level of organization; the longer the period of the rhythm.
These rhythmic activities result in the construction of 3 types of structural units
that are fundamental to plant form. The first - the cell is the source of other cells and of
other structural units. Their auto reproduction results in the formation of the meristems.
The meristems form the second - the metamers eg. The apical meristem of shoot
produces leaves, internodes, nodes and buds, these four are known as metamers.
The metamers form a more complex unit - the module. The modules are present
as combined units of morphologically similar metamers. The growth of module is either
terminated in an inflorescence, tendril or spine or in parenchymatous axis. Module
development continues only as long as the apical meristem is active. When it becomes
inactive it gives a stimulus for axillary bud to become active and thus bring about
branching of the module.
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The position of a module is a relative and not a fixed property. The addition and
growth of new modules causes the relative positions and state of the already existing
modules to change.
Combinations of modules construct an even higher level of organization the
system of shoot and roots. The spatial arrangement of modules determines the particular
morphology of systems. As many as 23 types of modules have been recognized in shoot
system of trees.
1.2.2 Difference between animal and plant Development Though, plants and animals both are made up of cells. The division of cell and the
nuclear set up is almost identical still they differ a lot in their mode of development.
1. Growth in plants is localized in meristematic regions, while in animals; it is
distributed all over the body.
2. Growth in animals ceases much earlier the death while in plants growth is
continued till death.
3. Plants develop as repetitive units of same structure in response to the
environmental factors and available space. On the contrary, animals have preformed
organs, which only increase in size and are not formed de novo.
4. Development of animals is more dependent upon the internal hormones,
external environment does not effect it significantly. In plants, the distribution of these
hormones in the plant body itself is affected by external environment.
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1.3 SEED GERMINATION
The seedSeed is the result of fertilization, which is formed in all spermatophytes
( gymnosperms and angiosperms). In gymnosperms, the ovules are exposed and so, also
the seeds. In angiosperms, the seeds are enclosed within the fruit.
1.3.1 Parts of the seed A mature seed consists of two essential parts- the seed coat and the embryo.
1) The seed coat The outer covering of the seed is known as seed coat. It develops from the
integument of the ovule. Mostly; it is made of the two layers- The outer thick and
leathery layer testa and the inner thin and papery layer tegmen.
The seed is attached to the pericarp (fruit wall) by a short stalk called seed stalk or
funiculus. In a mature seed, the position of seed stalk is marked by a small oval
depression called hilum. Just below the hilum is a small pore, the micropyle.
Seed coat has functions like 1) It protects the embryo from desiccation, unfavorable temperatures, mechanical injury
and attacks by bacteria fungi and insects.
2) Seed coat helps in seed dispersal by developing special structures in some plants such
as wings, hairs, fleshy colored tissues and air filled cavities.
3) Some seeds such as Pinus, contain starch and protein as a reserve food material which
are metabolized during seed germination
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2) The embryo The embryo is a young or miniature plant enclosed within the seed coat. It
develops from the fertilized egg. The embryo of a mature seed consists of 4 distinct parts.
Cotyledons, plumule, hypocotyl and radicle
The radicle, plumule and hypocotyl together form the embryonic axis or tigellum.
The cotyledons are attached to the embryonic axis. Dicotyledons typically
have two cotyledons, situated opposite to each other. Monocotyledons have only one
cotyledon which is often highly modified. In most of the plants, the cotyledons store the
reserve food material ( eg. Pea, gram, bean etc), and in others they also serve as
photosynthetic organs.
The part of the embryonic axis just above the point of attachment of the cotyledon
is known as epicotyl and at the tip of it is the plumule. It has1or more leaf primordia at its
apex.
The part, lying below the point of attachment is hypocotyl. It represents the root
stem transition region.i.e. The part where stem changes into root.
The radicle is the basal tip of the hypocotyl. When seed germinates, the radicle
becomes the primary root of seedling.
.
9
In seeds, food is stored in the cotyledons or in a special food storage tissue, the
endosperm. When endosperm is present the seed is known as endospermic or albuminous
seed. When the endosperm is fully utilized during the development of seed the seed is
known as non-endospermic or ex-albuminous seed.
Food materials stored in seeds are carbohydrates, proteins and lipids. On dry
weight basis seeds of cereals contain 70-80% starch, those of peas and beans about 50%
starch. In maize, principal food is starch but embryo contains 50% oil. The seeds of rape
and mustard contain 40% oil and 30% protein.
Carbohydrates Starch grains are found in amyloplasts. Large starch grains appear first and
smaller grains appear at later stages of development. Few outermost layers of endosperm
become highly specialized to form aleuron layers. Aleuron layers have thick walls and
non - vacuolated cytoplasm. They are interconnected by plasmodesmata.
Proteins In fabaceae, storage proteins are globulins. They occur as discrete protein bodies.
Protein bodies may lack inclusions or may contain globoids consisting of insoluble salts
of phytic acid, protein crystalloids, protein - carbohydrate bodies and calcium oxalate
crystals. Protein bodies accumulate in vacuoles.
Lipids Lipids are stored as oil bodies and triglycerides. Monomolecular layer of phospholipids
forms an interface with the surrounding cytoplasm.
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1.3.3 Germination of seeds The process by which the dormant embryo of the seed resumes active growth and
forms a seedling is known as germination.
1.3.4. Conditions necessary for germination
Seeds of all plants require supply of oxygen, water and favorable temperature for
the germination.
1. Oxygen - During germination embryo resumes growth and for this energy is required.
The energy comes from oxidation of food material.
2. Water - In dormant seeds, the food material is stored in concentrated form and they
have low physiological activity. Water is essential as the concentrated food is converted
in the form it can be utilized by the seedling. Water also serves as a medium where
enzymatic reactions occur. It also softens the seed coat and allows the embryo to come
out.
3. Temperature - A number of physiological processes occur within the seed during
germination. The favorable temp ranges from 20-350c.
1.3.5 The germination process Under favorable conditions, the seeds absorb water from the soil through
micropyle. The first visible indication is the swelling of seed, followed by the softening
of the seed coat.
Absorption of water causes a series of physiological changes. It first dilutes the
cell contents and there by activates enzymes. These enzymes convert the stored food
material into the soluble form that can be used by the growing embryo. Carbohydrates are
hydrolyzed by the activities of phosphorylase, amylase and maltase. Hydrolysis of starch
releases glucose, which is taken up by scutellum to polysaccharides that are transported
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to
growing
seedling.
Hemicellulose
is
hydrolyzed
to
mannose
and
other
monosaccharides.
During seed germination, protein is converted to amides and amino acids by
proteinases and peptidases. These smaller, more soluble compounds are translocated to
the embryo for their utilization.
While, lipases hydrolyze triglycerides, to glycerol and fatty acids; some of the
fatty acids are utilized to synthesize phospholipids and glycolipids which are required as
constituent of organelles, but most of the fatty acids are converted to sugars which are
utilized for growth of seedling.
Cell-division starts in the growing parts of the embryo (i.e., radicle and plumule)
when they get food material. The radicle is the first part of the embryo to come out of
the seed coat. It is positively geotropic and soon grows towards the soil regardless of its
initial orientation. With the expansion of embryo, the seed coat ruptures and the plumule
lying between cotyledons comes out. It forms the shoot.
On the basis of the behavior of cotyledons, the germination may be following
two types:
1. Epigeal germination- In seeds with epigeal germination the cotyledons are
brought above the ground due to the elongation of the hypocotyls. In cotton, papaya,
onion and castor, flat green leaf like cotyledons can be seen in the young seedlings. Here
the cotyledons, besides food storage, also perform photosynthesis till the seedling
becomes independent. In some other plants like tamarind and bean, the cotyledons being
thick, do not become leaf like; they shrivel and fall off.
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2. Hypogeal germination- In hypogeal germination the cotyledons do not
come out of the soil surface. In such seeds the epicotyl elongates pushing the plumule out
of the soil. All monocotyledons show this type of germination. The radicle and plumule
come out by piercing the coleoptile and coleorrhiza respectively. The plumule grows
upward and the first leaf comes out of the coleoptile. The radicle forms the primary root
which is soon replaced by many fibrous roots. Among dicotyledons, gram, pea,
groundnut, mango etc. are common examples of hypogeal germination.
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1.3.6 Nucleic acids Nucleic acids are found in very low amounts in storage tissue. These
nucleic acids are converted into nucleotides or nucleosides by the activation of the RNA
ase, DNA ase and polynucleotide phosphorylases .These nucleotides or nucleosides are
later transported to the embryo and converted into its nucleic acids.
1.3 .7 Hormonal control In many seeds, the presence of embryo is necessary for, or for increase, in
breakdown of products in the storage tissue; it shows that some stimulating factor is
supplied by the embryo. Researches on barley seeds indicate that Gibberellic acid, a
growth hormone, is involved in this process.
The embryo of seeds of cereal grains is surrounded by food reserves present in the
endosperm. The endosperm is surrounded by a thin layer of living cells, high in protein
content, called the aleuron layer. At the time of germination, seeds absorb moisture and
14
the aleuron cells become active. They provide the hydrolytic enzymes that digest the
starch, proteins and RNA and some cell wall materials present in the endosperm cells.
These smaller soluble compounds produced are then used by the embryo and it starts to
develop into seedling. These enzymes are β-amylase (already present in the aleuron
layer) α- amylase (synthesized when germination begins), ribonucleases and various
proteases (some are synthesized upon germination).
The developing embryo provides a gibberellins GA3, which induces the increase
in content of α-amylase and proteases in the aleuron layer, & activates β -amylase.
Actually, gibberllic acid act by causing formerly repressed genes to become active and
new enzymes are synthesized.
Gibberlic acid GA3, increases the rate of production of certain DNA molecules,
essential for growth. These DNA molecules are required for cell division and cell
elongation.
Some scientists have suggested that gibberellins act by promoting auxin
production. As the action of gibberllic acid upon gene activation in endosperm is similar
to the auxins. Both auxins, gibberellins along with cytokinins stimulate cell division. The
relative concentration of auxin and cytokinins together decide the type of tissue to be
differentiated.
The growth of the plant is a function of cell - wall formation. To achieve a certain
form, the walls usually grow at various rates, but still in pace of adjoining cells. So cells
divide, differentiate and form various types of meristems and there by tissues. They all
together form a seedling.
1.3.8. Gene Expression -
15
Any plant cell is capable of reproducing an entire plant. Because the
genetic make up of all the cells is identical, and so each cell possess the same genetic
information in the form of genes. All the cellular activities are direct products of genes
and of the enzymes produced under their control.
Then how is it possible that the cells arising from the same initials can have
different shapes and perform different functions? Why do not all cells with the same
genetic constitution possess identical amounts of identical enzymes at all times?
Let us consider the example of a single cell zygote which develops into a
complete organism. The control of development might be primarily internal, through
information within the zygote. Here, the DNA is activated in order to get ready for
division. DNA replicates in the presence of enzyme DNA polymerase, and by the help of
RNA polymerase, it forms mRNA, which then codes for proteins. So at any given time,
not all the genes are functional and only a few express themselves through mRNA, which
can produce specific enzymes. These specific enzymes catalyze the specific reactions.
There are two basic ways in which a cell can control its production of a given substance 1) A cell may change the effectiveness by which given enzyme can act,
2) It may alter the number of molecules of enzymes present to catalyze these reactions.
Gibberellins particularly GA3, is mainly responsible for enzyme production at the
time of germination. Studies indicate that it stimulates the synthesis of enzyme
α-amylase, which is necessary for starch utilization. The stimulation of enzyme synthesis
would be blocked by adding inhibitors of protein synthesis. Inhibitors of RNA synthesis
such as actinomycin D also prevent the GA3 stimulation. Abscissic acid is also effective.
So, Gibberellins act by causing formerly repressed genes to become active, and form a
16
new m RNA, molecules, and then new enzymes responsible for digesting and releasing
products of the endosperm. Similar effect is known to be caused by auxins before they
increase cell elongation. Both auxins and gibberellins along with cytokinins influence the
activity of repressor proteins through allosteric transitions.
1.4 TROPISMS As various organs are formed, their movements are of special interest. Why is it
that root always go into the soil, or the stem always moves towards light? The
movements of plant roots, stems, leaves and other parts in response to certain directional
fluxes or gradients in environmental factors are known as paratonic movements of growth
or tropisms. They are of following types –
1) Phototropism (Heliotropism) - The curvature induced in plant organs in response to the
unidirectional light is called phototropism. The unidirectional light causes the stem apex
to move towards the source of light and in root away from it. Thus the stem shows
positive phototropism and the root negative phototropism.
The positive and negative curvatures are
the result of the unequal growth of the illuminated
and shaded sides of the apex. In case of stem, the
growth is more on the shaded side, while in the
root it is more on the illuminated side. Greater
growth of the shaded side of the stem is due to
more accumulation of auxin on the shaded side.
This accumulation may be due to 1) Translocations of auxins from illuminated side
17
to shaded side.
2) Inhibition of auxin synthesis in the illuminated side.
2. Geotropism - The growth and orientation of stem and roots in response to the force of
gravity is called geotropism. Different parts respond differently to the stimulus of gravity.
The stem shows negative geotropism i.e. it grows away from the force of gravity and root
shows positive geotropism. Thus if a plant is kept horizontally, its stem will bend upward
and roots in downward direction.
Geotropism can also be explained on the basis of auxin concentration. In a
horizontally placed plant the auxin accumulates on the lower side of the stem and root
apices due to gravity. In the stems, higher conc. of auxin on the lower side of the apex
stimulates its growth on that side. As a result, the stem grows in upward direction
showing negative geotropism. In case of root, the higher conc. of auxin on the lower side
18
inhibits the growth of that side and the root apex grows downwards. i.e. show positive
geotropism.
Different plant parts respond to gravity in three ways 1) Orthogeotropic - Primary roots grow towards the force of gravity and are called
positively orthogeotropic. The main stem which grows away from the gravity is said to
be negatively orthogeotropic.
2) Plagiotropic - Secondary roots and branches arising from the main stem are at the
angle of 45-1800 from the
main axis. Thus, these organs are placed obliquely to the
force of gravity. Such organs are called plagiotropic. The secondary roots are positively
plagiogeotropic and the branches are negatively plagiogeotropic.
3) Diageotropic - Tertiary roots, horizontally placed branches and leaves arise at an angle
of 900 from the main axis. They are placed horizontally to the force of gravity and are
said to be diageotropic.
3. Hydrotropism – Growth movements in plant organs in response to variations in the
amount of moisture are
known as hydrotropism.
The curvature of organ
concerned
is
due
to
unequal growth on its two
sides. Roots are positively
hydrotropic.
19
4. Chemotropism - The movement of plant organs due to the unilateral stimulus of
chemicals is called chemotropism. The growth of pollen tube from stigmatic surface into
the style and ovary is due to chemical stimulus. Similarly, hyphae of many fungi show
positive chemotropism, they grow towards sugar and other nutrient substances.
5. Thigmotropism (Haptotropism) –
The
growth movement of plant organs in
response to unilateral stimulus of touch is
known as thigmotropism. Tendrils of many
cucurbitaceous plants nutate in the air and
when come in contact of any support, they
coil around it. The coiling occurs because the
growth of the surface which comes in contact
of the support is retarded while it remains
normal (or is accelerated) on the opposite
side.
1.5
USE OF MUTANTS IN UNDERSTANDING SEEDING DEVELOPMENT.
Using Arabidiopsis flower development, we can understand how a group of
undifferentiated cells in a floral meristems develop into a complete floral structure with
four types of floral organs and many different cell types.
It contains 4 whorls of organs- 4 sepals, 4petals, 6stamens and 2fused carpels. They are
known to be affected by three classes (A,B and C) of homeotic genes.
Class A gene is active in whorl 1&2—sepal and petal development
20
Class C gene is active in whorls 3&4--- stamen and carpel development
Class
B
gene
is
active
in
-
whorl
2&3—with
A
in
petal
development
---with C in stamen development
These specific gene classes include genes as AP I, AP2, AP 3, PI And AG. These genes
code for specific proteins. When mutants lacking any of these proteins are raised they
lack the corresponding floral whorl. These mutants have been proved as an effective tool
for decoding the mystery of floral development and differentiation.
1.6 LET US SUMUPNow, we are able to understand

The structure of seed, parts of seed, structure of embryo and the tiny plant present
in it.

Various types of food material present in the endosperm or in the cotyledons eg
Carbohydrates, lipids, proteins.
.

External factors as moisture, light, air, necessary for the germination of seed.

The mobilization of food materials from stored spaces to the embryo and their
conversion into simpler forms.

Utilization of these substances by the embryo cell, expression of functional genes
in meristematic tissue and differentiation of various tissues.

Hormonal and genetic control of functional and non- functioning of genes of an
otherwise totipotent cells.

Formation of metamers and modules as the structural units of organs.
21

Effect of external factors on whole plant. The whole plant as a whole unit respond
to the environmental factors as light, gravitational force, chemicals, water through
their movements - tropisms.

The whole development of the plant is a result of cumulative effect of external
and internal factors.
CHECK YOUR PROGRESS –
1.7
Write your answers according to the points given below.

1. If each cell has the potency to develop into a new plant, why cells are different
in structure and function?
Your answer should include1. Totipotecy
2. Hormonal control
3. Gene Expression

2. Describe effect of hormones in germination of seed.
Your answer should include!. Types of hormones.
2. Role of each hormone in seed germination.

. Describe tropisms.
Your answer should include1. Definition
2. Types
3. Causes
Multiple Choice QuestionsTick the correct answerCompare your answers with the answers given at the end22
Q.1 During germination, stem grows upward and root grows downward because(a) It depends upon light
(b) Of auxin
(c) It does not depend on light
(d) Of epinasty and hyponasty
Q.2 Thigmotropism is best exemplified by(a) Root apex
(b) Thorns
(c) Tedrils
(d) Lamina
Q.3 Scutellum is a (a) Endosperm of Gymnosperms
(b) Sheild-shaped cotyledon of monocots
(c) Protective covering of radicle
(d) Protective covering of plumule
Q.4 the tegmen of seed develops from (a) perisperm
(b) funicle
(c) inner integument
(d) outer integument
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Q.5 The embryonal axis is known as (a) Plumule
(b) hypocotyl
(c) epicotyl
(d) tigellum
1.8
ACTIVITIES1. Collect some seeds and find out the number of cotyledons and internal
anatomy.
2. Perform chemical analysis of these seeds.
3. Provide necessary conditions for their germination and find out the
percentage germination of these seeds.
4. Germinate some seeds in different pots, and put them in different
wavelengths of light, unilateral light, diffused light, dark conditions for a
week. Observe the results.
Hints for multiple choice questions1(b), 2 (c), 3 (b), 4 (c), 5 (d)
1.9 REFERENCES1. Seed technology –H.S. Tomar
2. Seed pathology- Paul Neergard
3. College Botany- Das , Dutta And Ganguly
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4. Bidwell,R.G.S. Plant Physiology Macmillan Publishing co., Inc. New York.
5. Devlin, R.M. Plant Physiology. Reinhold Publishing Co., Inc. New York.
6. Noggle G. R. and Fritz Introductory Plant Physiology
7. Verma S.K. Plant Physiology and Biochemistry. S.Chand Publications
8. Malik C.P. and A.K. Shrivastava Textbook of Plant Physiology
9. Purohit S.K. Plant Physiology
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