CELL CONTENTS
In pharmacognosy, the cell contents which can be identified in plant drugs by microscopical and
physical tests. These are either food storage products or the by-products of plant metabolism and
include carbohydrates, proteins, lipids, calcium oxalate, calcium carbonate, tannins, resins, etc. Some
of these cell contents of diagnostic importance can be briefly described as follows.
Starch
Starch is present in different parts of the plant in the form of granules of varying size. Starch is found
abundantly in fruit, seed, root, rhizome and as smaller grains in chlorophyll containing tissue of the
plant such as leaf. Starches of different origins can be identified by studying their size, shape and
structure, as well as, position of the hilum and striations. Chemically, starches are polysaccharides
containing amylopectin and β-amylose. Starch turns blue to violet when treated with iodine solution.
Starches of pharmaceutical interest are obtained from maize, rice, wheat and potato. These starches
can be differentiated from each other by microscopical examination. A comparative account of their
macroscopical, microscopical and physical characteristics is given in the Table below. For purpose of
microscopical studies, the powder should be mounted in Smiths starch reagent containing equal pa
Table : Characteristics of some starch grains
A systematic description of starch grains should include:
1) Shape : Ovoid, spherical, sub-spherical, ellipsoidal, polyhedral, etc.
2) Size : Dimensions in μm.
3) Position of hilum : Central, eccentric, pointed, radiate, linear, etc.
4) Aggregation : Simple, compound; number of compo-nents present in a compound grain.
5) Appearance between crossed polaroids.
6) Location : Loose, present in type of cell and tissue.
7) Frequency : Occasional, frequent, abundant.
Aleurone Grain
Protein is stored in the form of aleurone grain by plants. Aleurone grain
consists of a mass of protein surrounded by a thin membrane, and is
found abundantly in the endosperm of the seed. The ground mass of
protein, however, often encloses an angular body (crystalloid) arid one or
more rounded bodies (globoids).
Defat thin sections containing aleurone grains and treat with the following
reagents.
1. Alcoholic picric acid—Ground tissue and crystalloid are stained yellow.
2. Millon’s reagent—Protein is stained red on warming.
3. Iodine solution—Only crystalloid and ground substance are stained yellowish brown.
Calcium Oxalate Crystals
Calcium oxalate crystals are considered as excretory prod-ucts of plant metabolism. They occur in
different forms and provide valuable information for identification of crude drugs in entire and
powdered forms.
1. Microsphenoidal or sandy crystals—Belladonna.
2. Single acicular crystals—Cinnamon, gentian
3. Prismsmatic crystals—Quassia, hyoscyamus, senna, rau-wolfia, cascara.
4. Rosettes crystals—Stramonium, senna, cascara, rhubarb.
5. Bundles of acicular crystals—Squill, ipecacuanha.
The sections to be examined for calcium oxalate should be cleared with caustic alkali or chloral
hydrate. These reagents very slowly dissolve the crystals, so the observa-tion should be made
immediately after clearing the section. The polarizing microscope is useful in the detection of small
crystals.
Mount the cleared section or powder in the following reagents and observe the crystals.
1. Acetic acid—Insoluble
2. Caustic alkali—Insoluble
3. Hydrochloric acid—Soluble
4. Sulphuric acid (60% w/w)—Soluble, on standing replaced by needles of calcium sulphate.
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pharmacognosy/cell-wall-constituents/43942966
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