Download PLANT CELL WALL AND Contents

Cell wall
A cell wall is a fairly rigid layer surrounds a cell and located external to the cell membrane, which
provides the cell with structural support and protection. The cell wall also prevents overexpansion when
water enters the cell. They are found in plants, bacteria, archaea, fungus, and algae.
Animals and most protists do not have cell walls.
In plants a cell wall plays mostly a mechanical support role rather than a role as a selective boundary
N.B. The cell membrane (plasma membrane) surrounds the cytoplasm of a cell and physically
separates the intracellular components from the extra cellular environment, thereby serving a function
similar to that of the skin
THE PLANT CELL WALL
In plants the cell wall is constructed from different
materials dependent upon the species. During the
differentiation of the cell, the original cell wall may
undergo various chemical modification, which
change its physical properties. In plants, the cell
wall is constructed primarily from a carbohydrate
polymer called cellulose
(in bacteria the cell wall is peptidoglycan. Fungi
possess cell walls of chitin. Algae typically possess
walls constructed of glycoproteins )
The principal modifications are the deposition of ;
Further cellulose, Hemi-cellulose, Lignin, Cutin,
Suberin, Mucilage, and Chitin
CELLULOSIC CELL WALL
Cellulose is the most abounded carbohydrates; it
form 50% or more of all the carbon in plants.
The cellulose molecules is an insoluble un-branched
polysaccharide consisting of about 10,000 glucose
unites .
Color reaction of cellulose: i-Gives a blue color with
chlor-zinc-iodine
ii-Dissolved in ammoniacal solution of copper
oxide
iii-Give no color with phloroglucinol & HCL
HEMI – CELLULOSIC WALL
Group of polysaccharides that are more soluble
than cellulose
They are vary in there chemical composition from
one species of plant to another
Cellulose fibers are cement together by a matrix of
Hemi-cellulose
Color reaction of Hemi-cellulose:
i-Blue color with iodine
ii-Insoluble in ammoniacal solution of copper oxide
LIGNIFIED CELL WALL
Composing as much as 35% of the dry weight of the
secondary cell wall
Extremely complex polymer composed of complex
molecule derived from certain amino acid (named
phenyl-propanoid )
Strengthening material which formed the cell wall
of tracheids, vessels, fibers and sclereids of vascular
plants
Color reaction of lignin:
i-Phloroglucinol & HCL stains lignified walls pink or
red ii-Acid aniline sulphate stains lignified walls
bright yellow
iii-Chlor-Zinc-iodine stains
lignified walls yellow
SUBERIZED CELL WALL
Suberin is waterproof material, formed from highly
polymerized fatty acids called suberic acid
Found in cork cells and endodermal cells
CUTINIZED CELLWALL
Cutin form a secondary deposit on primary
cellulosic wall
Leaves are covered with a deposit of cutin which
may show characteristic papillae
Color reaction for both suberin & cutin:
i-Yellow to brown color with Chlor-zinc-iodine
ii-Red color with Sudan III
iii-Strong solution of potash stains suberin and
cutin yellow
vi-Dilute tincture of alkanna stains the walls red
MUCILAGINOUS CELL WALL
The cellulosic cell wall, in this case, is transformed
into a gelatinous mass of carbohydrate in nature,
namely gum or mucilage
Mucilaginous walls are found in the epidermal cells
and center of the pith in the gum yielding species of
some plants
Chemically, mucilage is a complex molecules of
sugars e.g. glucose, arabinose and xylose
With ironic acid combined with metals
Color reaction: i- Yellow color or granular
precipitation with lead subacetate
CHITINOUS CELL WALL
Chemically chitin is formed from a complex unites
of N-acetyl gloucosamine joined by glycoside bonds
Chitin forms the major part of The cell wall of
insects and many fungi, e.g. Ergot
Color reaction of chitin:
Chitin, when heated with 50% of KOH at 160-170
degree for one hour it is converted
to Chitosan , which gives violet color when treated
with 5% iodine solution then with 1% sulphuric acid
ERGASTIC CELL CONTENT
Plants and other photosynthetic organisms convert
Carbon dioxide into billions of tons of organic
molecules
Chemical energy stored in these molecules and
fuels the metabolic reactions that produced either
food-storage products or by-products of
metabolism include: Carbohydrates, proteins, fixed
oil and fats, alkaloids, glycosides, gums mucilage,
volatile oil and resins, tannins, Calcium oxalate,
These by-products of the plant cell metabolism,
being nonliving they are referred to as ergastic
STARCH
Starch is the typical form of carbohydrate used for
energy storage in plants and formed in special cells
called chloroplasts
It is a polymer of glucose unites occurs in two forms
of different size: Amylose (un-branched glucose
units) and Amylopectin (branched chain)
Starch occurs in almost all organs of plants; it is
found most abundantly in roots and rhizomes
Starch gives blue to violet color with iodine solution
The common types found in powder drugs are: iMaize starch ii-Potato starch iii-wheat starch iv-Rice
starch
PROTEINS
Portions are the most common cell components,
developed in the cell as macromolecules. It is
composed of amino acids (nitrogenous organic
substances)
Proteins are involved in all aspects of plant cell
metabolism
It stored in the plant cell in the form of aleurone
grains which well seen in oily seeds e.g. caster seed
and linseed
Aleurone grain consists of a mass of protein
surrounded by a thin membrane, embedded in the
ground protein are a rounded bodies (globoids) and
angular bodies (crystalloid)
All proteins are insoluble in organic solvents and
precipitated by salts of heavy metals and by tannic
acid
Proteins gives red color with Millon’s reagent,
yellow color with picric acid and violet color with
20% NaOH and copper sulphate solution
FIXED OIL AND FATS
They are reserved food materials, occurs in the
plant in the form of glyceryl (esters of fatty acids
with glycerin)
They are greasy, non volatile, viscous liquid,
semisolids or solids
Insoluble in water, soluble in ether, chloroform and
petroleum ether
Hydrolyzed by aqueous alkalis, giving salt of fatty
acid (soap) and glycerin
Fixed oil & fats stained red with tincture alkanna &
sudan III also stained brown to black with 1%
osomic acid
ALKALOIDS
Alkaloids are basic nitrogenous compounds, contain
1 or more nitrogen atoms usually in heterocyclic
ring
Alkaloids usually have a physiological action on man
or other animals e.g. nicotine in tobacco
Tests for alkaloids: i- With Mayer’s reagent
(potassium mercuric iodide) gives cream PPT
ii- With Wagner’s reagent (iodine/KI) gives brown
PPT iii- With Dragendorff’s reagent ( potassium
bismuth iodide) gives reddish PPT iv-With solution
of tannic acid gives dirty white PPT v-With
saturated solution of picric acid gives yellow PPT
GLYCOSIDES
Glycoside is an organic compound of plant origin
consisting of a sugar part linked to non-sugar which
known as aglycone
Glycoside can be hydrolyzed either by acids or
enzymes emulsin to give chemically different
aglycone
These differences is the bases of the chemical
classification of glycosides into:
1- Phenolic glycosides found in uva ursi leaves 2Antheracene glycosides found in senna leaves
3-Flavonoid glycosides found in buchu leaves 4Cyanogenetic glycosides Found in bitter
almond 5-Thio glycosides found in muster
seeds 6-Cardiac glycosides found in digitalis
leaves 7-Saponin glycosides found in quillaia
bark
GUMS AND MUCILAGE
Gums and mucilage are polysaccharide complexes
formed from sugar & uronic acid and frequently
combined with metals
They are insoluble in alcohol but dissolve or swell in
water e.g. gum tragacanth
Specific color reactions are: 1-Mucilage of senna &
buchu leaves stained red with Ruthenium red
reagent
2-Muciage of squill stained red with alkaline
solution of corallin soda
VOLATILE OIL AND RESIN
Volatile oils occur as droplets inside the cell, they
are soluble in alcohol but sparingly soluble in water
Resin may be found alone as irregular masses in the
cell or may be associated with volatile
oils in the form of oleoresins or associated with gum
to form gumresins
They stain slowly with dilute tincture of alkanna or
with iodine solution
TANNINS
Tannins are widely distributed in the plants and
occur in the cell sap, they are soluble in water and
in alcohol
Tannins classified into two groups:
1-Hydeolysable tannins (Pyrogallol tannins) These
group hydrolysable by acids or enzymes, give blue
color with ferric chloride and present in clove, galls,
bearberry leaves and pomegranate bark
2-Condensied tannins )(catechol tannins These
group include all other tannins which resist
hydrolysis with acid and enzymes, give green color
with ferric chloride and present in tea, hamamelis
leaves, cinnamon and cinchona bark
CALCIUM OXALATE
Very common cell content in the plant kingdom
It is formed in the cell as a result of the reaction of
calcium salts absorbed from the soil and oxalic acid
produced in the plant as a result of the metabolic
process
Since the formed calcium oxalate is insoluble in
water and in the mild acid cell-sap, it is deposited in
crystalline form
Calcium oxalate crystals are insoluble in water,
alcohol or acetic acid but dissolves in HCL with out
effervescence (distinction from calcium carbonate).
The crystals decomposed with 20% sulphuric acid
with formation of needle-shaped crystals of calcium
sulphate
FORMS OF CRYSTALS
Different forms of calcium oxalate afford a valuable
aid in the differentiation of drug even in the powder
forms i-Prisms crystals as in quillaia, cascara, and
frangula barck ii-Cluster crystals as in senna leaf iii-
Acicular or needle- shape as in Ipecacuanha root
crystals iv-Sandy crystals as in cinchona barck vSphaero-crystal