PLANT ANATOMY

Lecture 1

Plants are the living, multicellular, eukaryotic

organisms, which belongs to the kingdom

Plantae.

There are more than 300,000 species of plants. Plants play a key role in the history of life on planet earth. Plants are the main responsible for the addition

of oxygen gas to the atmosphere • They are the only source of food for

both animals and humans. They are the primary habitat for millions of other organisms. A plant is living which produce their food by photosynthesis.

• Plants provide shelter, safety, place, food for animals.

Plant anatomy can be defined as a branch of

botany, which is

concerned with the study of internal structure

of plants.

• It is also called as Phytotomy. • Plant anatomy is a Greek word, which means dissection "to cut to

pieces". • It completely deals with the structural organization of plants.

Plant anatomy is the study of the shape,

structure, and size of plants.

• A typical plant body consists of three major vegetative organs: ROOT

STEM

FRUIT • As well as a set of reproductive parts that include flowers, fruits, and

seeds.

Lecture - 2 1. The Tree of Life

According to the fossil record, the most primitive organisms known- the bacteria and the

cyanobacteria date back over 3 billion years.

The first land plants & insects over 400 million years, the first birds and mammals over 180

million years.

The living things classified into five kingdoms as shown in the diagram. The kingdoms can

be subdivided into smaller groups called phyla (singular phylum). For some kingdoms, only

one phylum is given as an example but for others there are several. The Plant Kingdom

includes the angiosperms (flowering plants), gymnosperms (cone-bearing plants, fens and

bryophytes (mosses &liverworts). Recent classification systems suggest that Fungi Kingdom

these organisms, in addition to the red algae and green algae, should be classified in the Plant

Kingdom.

2. What is the Plant?

A plant:

A. Is multicellular

B. Is non-motile:- not capable of independent movement

C. Has eukaryotic cells:- cells have distinct membrane-bound organelles, including a nucleus

with chromosomes.

D. Has cell walls comprised of cellulose

E. Is autotrophic:- capable of sustaining itself through conversion of inorganic substances to

organic material

Plant Structure

Angiosperms (Flowering plants) are the most diverse group of plants known (over 275.000

named species and thought to be at least that many more unknown to science). Within the

Angiosperms, there are two plant groups, the Monocots and the Dicots. The distinction

between these two groups is not always clear, but some general trends are outlined below:

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Monocot Dicot

Leaf Venation Parallel Net

Vascular bundles Scattered Ring

Habit Herbaceous Herbaceous+Woody

Roots Fibrous Taproot

Growth Primary only Primary and secondary

Example Grass, palm, Wheat Oak, Rosses, Sunflower

A plant has two organ systems:

1. Shoot system; includes the organs such as leaves, buds, stems, flowers (if the plant has

any), and fruits (if the plant has any).

2. Root system; includes those parts of the plant below ground, such as the roots, tubers, and

rhizomes.

Plant Cell Components

Cells are the foundation of plants. Like the bones in the body, the cell wall provides the

framework for the plant. The walls of the cells actually create the structure of the plant. The

understanding of cells will form the base of our understanding of Botany then plant physiology.

I- Cell Wall (extra cellular matrix):

I- Rigid structure that defines shape of cell.

2- Provides rigidity and strength to plants.

3- Allows plants to grow tall and withstand forces such as wind& gravity

4- Allows cells to build up internal (turgor) pressure which adds stiffness to cell/plant.

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Primary & Secondary Cell Walls (CW):

1- All cells have primary CW

2- Some mature cells develop secondary cell wall.

Cell plate

The cell plate is a thin layer of largely pectic materials laid down across the phragmoplast,

the microtubular structure that forms midway between the two nuclei and disassembling

spindle during cytokinesis.

The cell plate grows in the region of the phragmoplast where the ends of the microtubules

overlap and eventually is in continuity with the already existing wall.

Cell plate formation consists of the creation of a plate like membranous network that is

derived from the fusion of Golgi-derived vesicles in the equatorial plane. As more pectic

substances are synthesized by the dictyosomes (Golgi apparatus) and transported to the cell

plate in vesicles, the cell plate is transformed into the middle lamella. The middle lamella:

Acts as an intercellular to bind the walls of daughter cells together. It is regarded as the first

true cell wall layer. This layer consists largely of highly hydrated, pectinaceous substances

and can be identified as an extremely thin layer between two adjacent cells. The middle

lamella is optically isotropic, which means that it is composed of substances having the same

optical properties along all axes.

The Primary Wall

The primary wall is the first readily visible layer of the cell wall, and its formation accompanies

extension growth. It develops on either side of the middle lamella when two cells are adjacent

and largely determines cell shape and size during plant growth and development.

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Primary Cell Walls are made of:

1 ) Cellulose

2 ) Hemicelluloses

3 ) Pectin

Secondary Cell Wall, particularly those with strengthening and supporting functions,

continue to add wall material inside the primary cell.

Secondary Cell Walls are:

Deposited after cells have stopped growing. .

Cellulose microfibrils are oriented (not random) Composition is different from

Primary CW.

More rigid than Primary CW.

Secondary Cell Walls are made of: 1 ) Cellulose 2 ) Hemicelluloses 3 ) Lignin

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Lecture 3

Plant Cell Organelles

https://www.youtube.com/watch?v=URUJD5NEXC8

1. Plasma or Cell membrane

Cell boundary; selectively permeable; bilayer of phospholipids with inserted protein.

Phospholipids are unique molecules they are amphipathic, meaning that they have both

hydrophilic and hydrophobic regions. As a result plant phospholipids usually have a higher

degree of unsaturation than animals.

The function of the membrane is to:

Regulate traffic.

Separate the internal from external environment.

Serve as a platform on which some reactions can occur

Participate in some reactions (i.e., the membrane components are important

intermediates or enzymes).

Provide some structural integrity for the cell

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2. Nucleus

The cell "brain". Surrounded by a double membrane (two phospholipid bilayers) - the nuclear

membrane.

Have pores. The structure of the pores is complex comprised of a more than 100 proteins.

3. Cytoplasm/Cytosol

The cytosol is the gel-like matrix within the cell in which the other structures are embedded.

The cytoplasm refers to the cell materials inside the membrane.

4. Mitochondria

Mitochondria are found in all eukaryotic cells. They are the sites of cellular respiration-

process by which energy is released from fuels such as sugar. Mitochondria is the power plan

of the cell. A popular misconception is that "plants have chloroplasts, animals have

mitochondria. Plant cells, at least green plant cells (i.e., leaf cells), have both. Root cells only

have mitochondria. The inner membrane differs from the plasma membrane in that has higher

protein content (70 %) and unique phospholipids.

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5. Ribosome

Sites of protein synthesis (translation).

6. Endoplasmic reticulum

A series of membranous tubes and sacs (cisternae) that run throughout the cell. Rough ER

has ribosomes while smooth ER lacks ribosomes and is tubular.

The ER bas several functions including:

Synthesis of lipids and membranes (smooth ER);

Serving as a site for the synthesis of proteins by the ribosomes (rough ER)

Transport (a type of cell 'highway systemy, and

Support

7. Peroxisomes

Membrane sac containing enzymes for metabolizing waste products from photosynthesis, fats

and amino acids. A major function of the peroxisome is the breakdown of very long chain

fatty acids through beta oxidation.

8. Golgi apparatus

The Golgi is active in synthesizing many cell components, especially carbohydrates and is

involved in tagging proteins with carbohydrates and other side chains for sorting them to

their final destination.

9. Microtubules

Microtubules are involved in the cell cytoskeleton (for support), cell movements and cell

division.

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10. Microfilaments

Protein strands. Solid. Made from G-actin. Involved with the cell cytoskeleton. Main

function is support. They are about 7 nm in diameter.

11. Others

Organelles Unique to Plants

An organelle is a tiny cellular structure that performs specific functions within a cell.

1. Plastids

Plastids are double membrane-bound organelles in plants. They contain their own DNA and

ribosomes. They are semi- autonomous and reproduce by fission similar to the division

process in prokaryotes. The plastid DNA carries several genes including the large subunit of

rubisco and those for resistance to some herbicides.

2. Vacuoles

This is the large, central cavity containing fluid, called cell sap, found in plant cells.

The vacuole is surrounded by a membrane (tonoplast).

The vacuole is penetrated by strands of cytoplasm - transvacuolar strands.

The tonoplast and plasma membrane have different properties such as thickness (tonoplast

thicker) so every plant cell has a large, well-developed vacuole that makes up to 90 % or

more of the cell volume.

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Important roles of the vacuoles are:

Energetically efficient means to increase surface to volume ratio in the dendritic

growth from since 90 % of the cell volume is vacuole, therefore 90% of the cell is

water which is relatively cheap in metabolic terms.

Water storage: - Probably a minor role: mostly in succulent plants.

Waste disposal: The vacuole can be considered the cell cesspool. It contains many

secondary metabolites.

Organelle Function

Cell Wall Supports and protects the cell

Nucleus Stores heredity information in DNA; Synthesis RNA & Ribosomes

Mitochondrion Transfers energy from organic compounds to ATP

Vacuole Stores enzymes & waste products

Plastids Stores food or pigments; one type (Chloroplast) transfers energy form

light to organic compounds

Ribosome Organizes the synthesis of proteins

Endoplasmic Prepares proteins for export(Rough ER); synthesis steroids, regulates

reticulum (ER) Calcium level, breaks down toxic substances (Smooth ER)

Golgi Apparatus Process & Packages substances produced by the cell

Microfilaments& Contribute to the support. Movement, and division of cell

Microtubules

Cilia & Flagella Propel cells through the environment; move materials over the cell surface

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Lecture 4

Plant Tissue

A group of similar or dissimilar cells having a common origin and performing a similar

function.

A. Meristematic tissue

The term meristem has been derived from a Greek word meristos- which means

divisible or having cell division activity, so meristem is a group of cell which

has power of continuous division.

Meristems are the site of formation of new cells within the plant. eg.: meristem

at apex of stem, root and vascular cambium, etc. .

The term meristem was given by C. Nageli (1858) for group of continuously

dividing cells.

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Characteristics of meristematic cell:

1- Living cells found in vegetative regions of the plant

2- They have thin walls of cellulose.

3- Cells are normally isodiametric, oval, polygonal or rectangular

4- Abundant cytoplasm is present, vacuoles are either absent or very small, large nucleus is

present and their plastids are in proplastid stage. 5- Cells are compactly arranged and lack intercellular spaces.

6- Cells have the capacity to divide.

Classification of merestimatic tissue

Meristematic tissues may be classified on the basis of:

(a) Origin and development

(b) Position in the plant body

(c) Plane of division

(d) Functions

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(a) Meristems based on origin and development:-

(i) Promeristem (primordial meristem):

A group of cells which represent primary stages of meristematic cells. They are present in

a small region at the apices of shoots and roots. They give rise to primary meristems.

(ii) Primary meristem.

The meristematic cells that originate from promeristem are primary meristems. In most

monocots and herbaceous dicots, only primary meristem is present.

(iii) Secondary meristem:

They are the meristems developed from primary permanent tissue.

They are not present from the very beginning of the formation of an organ but develop at

a later stage and give rise to secondary permanent tissues. Examples: Cambium of roots,

interfascicular cambium of stem and cork cambium.

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Meristems based on position in plant body:

1- Apical meristem : It is found at the apex of growing points of root and shoot.

It divides continuously and brings about growth in length of shoot and root.

The apical meristem includes promeristem as well as primary meristem.

2- Intercalary meristem : It is present away from apical meristem.

It is present at the base of internodes e.g.; in grasses and wheat (Gramineae) or at the

base of leaves e.g.; in Pinus or at the base of nodes e.g mint or Mentha (Labiatac). It

is responsible for increase in length.

3- Lateral meristem : They are located parallel to the long axis of the plant organs.

Their activity results in increase of the diameter of the plant organs, e.g.; Cork

cambium and Vascular cambium.

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(b) Meristems based on plane of division:

It includes three types of meristems:

(i) Mass meristem: In this cell division occur in all planes so that an irregular

shaped structure is formed e.g. endosperm.

(ii) Plate meristem: It is consisted of parallel layers of cell which divide anticlinally

in two planes so that a plate-like structure formed. This pattern is seen in the

development of leaf lamina

(iii) Rib meristem: In this type, cells divide at right angles in one plane. It is found in

the development of lateral roots.

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(c) Meristems based on function:

(i) Protoderm: It is the outermost layer of the young growing region which

develops the epidermal tissue system

(ii) Procambium: It is composed of narrow, elongated cells that give rise to the

vascular tissue system that is xylem and phloem.

(iii) Ground meristem: It consists of large, thin-walled cells which develop to

form ground tissue system that is hypodermis, cortex and pith.

Anticlinal and periclinal cell division are both different ways of cell division. Now let's

understand the difference between the two.

Periclinal cell divisions are the ones that occur parallel to the tissue or organ surface. As a

result, we get rows of cells stacked one over the other.

Anticlinal layer of cells. So, what you get is columns of cells adjacent to one another. In

simple words, anticlinal division adds more thickness and periclinal division adds length

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Lecture 5

Theories of Shoot and Root Apex Organization:

A. Apical Cell Theory

According to this theory, a single apical cell is the structural and functional unit of apical

meristem. All other cells are derivatives of this single cell. This theory is applicable only to

some higher algae, bryophytes and pteridophyta but is not applicable to gymnosperms and

angiosperms plants.

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B. Histogen Theory

This theory was given by Hanstein (1870). According to his theory, shoot and root apex has

growth zones, which are called histogens.

They are of the following types:

1- Dermatogen (outermost): Gives rise to epidermis or rhizodermis in root.

2- Periblem (middle): Gives rise to cortex including endodermis.

3- Plerome (innermost): Gives rise to vascular tissue including pith.

4- Calyptrogen: only in root apex. It gives rise to the root cap in monocots.

There is an inactive centre in the root apex which is called quiescent centre (having low

DNA, RNA and proteins) and it acts as reservoir of active initials.

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C. Tunica -Corpus Theory:

Shoot and root apex has two regions

(i)Tunica: It is generally single layered outer region, it divides only anticlinally. In

multilayered tunica, the outermost layer forms the epidermis and rest of the layers from

cortex and leaf primordia. Its cells are small.

(ii) Corpus: The inner mass of cells is called corpus. It divides both anticlinally as well

as periclinally. Its activity results in the formation of cortex and stele. The cells of corpus

are larger and divide to result into increase in volume.

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B. Permanent tissues

It is formed due to divisicn and differentiation in meristematic tissue.

The cells of this tissue may be living or dead thin-walled or thick-walled. The thin-walled

tissues are generally living whereas the thick-walled tissues may be living or dead

Types of permanent tissues

(a) Simple tissue (b) Complex tissue

(c) Special tissue

A. Simple tissues

These are homogenous in nature and are composed of structurally and functionally similar

cells these are of three topes:

(i) Parenchyma

(ii) Collenchyma

(iii) Sclerenchyma

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(i) Parenchyma

Parenchyma is considered as the precursor of all other living tissues.

It is also the most primitive tissue from phylogenetic point of view.

Parenchymatous cells are living thin-walled containing distinct nuclei.

The cell walls are made up of cellulose hemicellulosic and pectic materials.

Cells have small or large intercellular spaces. Cells are generally isodiametric (but

may also be elongated lobed, columnar, stelate and folded).

All meristems made up of parenchyma.

Functions:

1-Parenctyma cells are the centre of respiration, photosynthesis, storage, secretion etc..

2-These cells may have the power of division.

3- These cells help in wound-healing and in formation of adventitious buds and roots.

4-Parenchymatous cells store water in succulent plants.

5- In aquatic plants parenchyma cells store air.

6-Parenctyma cells of xylem and phloem help in conduction of water and food materials.

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Specialized Parenchyma

A. Prosenchyma

Parenchyma cells are elongated.

Found in pericycle of roots.

Its function is to provide strength

B. Chlorenchyma

When parenchyma cell is containing chloroplasts, it is known as chlorenchyma.

Examples - leaf mesophyll tissue, outer cortex of young stem, outer cortex of xerophytic stem

etc.

Its function is to manufacture food material (photosynthesis)

C. Aerenchyma:

In hydrophytes, the parenchyma develops air spaces and such parenchyma with air cavities is

known as aerenchyma.

It helps hydrophytes to float and provides O2, for respiration.

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D. Idioblast:

This type of parenchyma non-living ergastic substances like tannins, oil, crystals etc, is found

in stored form.

Its function is to store ergastic substances.

D. Mucilaginous parenchyma:

It has large vacuoles and mucilage e.g. Succulents.

Its function is storage of water.

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Chlorenchyma and storage parenchyma

(ii) Collenchyma

1-These are living elongated cells with thick walls. The cell wall is made up of cellulose,

hemicellulose and pectic materials. The wall thickening is not uniform.

2- The walls are often provided with simple pits. Sometimes chloroplasts are present in

Collenchyma cells.

3- Collenchyma is found in many herbaceous dicot stems, petioles and younger aerial

regions of woody stems.

4- Collenchyma is absent in roots and monocot stems.

Types of collenchyma:

According to thickening on cell wall, Collenchyma may divide into three types:

A. Angular The deposition is maximum at the angles (where the two cell walls come in

contact). It is the most common type.

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B. Lacunar: Large intercellular spaces occur between the cells. The deposition occurs on the

walls towards the spaces.

C. Lamellar: The deposition occurs on tangential walls. The cells appear plate like or lamellar. It

is also called plate collenchyma. Functions It performs both mechanical as well as vital types of

functions. Collenchyma provides tensile strength which gives elasticity and support to the

growing organs chloroplast containing collenchyma performs photosynthetic function.

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(iii) Sclerenchyma

They are dead cells, and act as purely mechanical.

The cells are long, narrow and pointed at both ends.

The cell walls are lignified and have simple pits.

The cell walls are very thick with the result that the cell cavity becomes narrow.

Types of Sclerenchyma:

There are two types:

A. Fibers

B. Sclereids

A. Fibers

Cells long, narrow and thick walls pointed at both ends and lignified.

Cell wall has simple or bordered pits.

Generally, length of the fibers is up to 3 mm but in some cases like jute, flax and hemp fibers

are up to 20-550 mm in length.

The fibers present outside xylem are called extra-xylary fibers.

They are five types:

1- Cortical fibers in cortex

2- Pericyclic fibers in pericycle, Pericyclic fibers are also called perivascular fibers.

3- Phloem fibers in phloem. Phloem fibers are also called bast fibers.

4- Bundle sheath fibers.

5- Septate fibers: are long lived fibers occurs in phloem in some plants.

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Hard fibers and Soft fibers

(i) Hard fibers: the hard fibers are monocot leaf fibers with very thick lignified walls.

(ii) Soft fibers: are bast fibers e.g.; Hemp, Flax. Jute, etc.

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B. Sclereids

These are not much longer than their breadth (width).

They have also extremely thick wall.

Types of Sclereids

(a) Brachysclcreids or Stone cells

These are small, oval or rounded cells.

They are found in cortex, phloem and pith of stems and fleshy pericarp of certain fruits (e.g.

pear, apple, and guava).

Stone cells are also present in hard parts like endocarp of coconut and hard seed coats.

(b) Macrosclereids:

These are rod- like or columnar cells.

They are common in the seed- coats of many leguminous plants (e.g pea).

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(c) Ostcosclercids:

These are bone- shaped cells and look like as bones.

They are found in leaves and seed-coats of several monocotyledons.

(d) Asterosclereids:

These are star shaped cells.

They are found in the petioles of Nymphaea.

(e) Trichosclereids: These are hair-like, branched or un branched cells.

They are found in the intercellular spaces of leaves and stems of some aquatic plants.

Sclereids provide mechanical strength to the part of the plant where they are present.

They contribute to hardness of the part concerned.

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