Chemotaxonomy of Medicinal plant

CHEMOTAXONOMY:

Definition:-The approach of taxonomy in which chemical nature of plants are used in

developing classification or in solving taxonomical problems is called chemotaxonomy

,chemosystematics, chemical taxonomy ,chemical plant taxonomy or plant chemo taxonomy

are the common names of chemotaxonomy.

It gives the close relationship between chemical constituents of plants and their taxonomical

status.

_ Chemotaxonomy establishes relationship between the position of the plant and exact

understanding of biological evaluation and natural relation ship.

_ Depending upon chemical evidence, plants are classified accurately as alkaloids,

flavonoids, carotenoids, polysaccharides, terpenoids, fatty acids (proteins).

Purpose of chemotaxonomy:-

_ Chemotaxonomy has been used in all levels of classification. Chemical evidences have

been used in all the groups of the plant kingdom starting from simple organism like fungi and

bacteria up to the most highly advanced and specialized group of Angiosperms.

_ The evidence is used in classification of plants into 2 main purposes.

1. To improve the existing system of plants differentiation.

2. To develop the present day knowledge of natural relationship of plants.

o Chemical characters and their use in taxonomy: -

Naik divided the chemical characters into 3 categories.

1. Directly visible characters:-Starch grains, raphides, silica ,gypsum ,etc

2. Chemical test characters:-phenolic ,betalins, oil fats, waxes ,alkaloids

3. Proteins

o On the other hand in 1987 some authors divided the natural chemicals plants

products into 2 groups on the basis of molecular weight.

1. Low molecular weight compounds:- That is a molecular weight of 1000 or less than 1000

called as Micromolecules. Ex:-Amino acids, alkaloids, fatty acids, terpenoids, flavonoids.

2. High molecular weight compounds:- with a molecular weight of more than 1000 called as

Macromoecules. Ex:-proteins, DNA, RNA complex , Polysaccharides.

History of Chemotaxonomy:

The concept of classification of plant based on chemical character is not new. It is started in

15th &16th centuries by anatomist Newmann, Grew & James petitver. They recognized

similar chemicals or medicinal effects of umbelliferous plants.

Greshoff in 1909, suggested that chemical characters should be included in natural

classification.

Baker and Smith in 1920, worked on single genus Eucalyptus (176)-collected

morphological and chemical data and finally concluded on the morphological basis the

feather contended leaves having more pinene in their volatile oil.

Mc Nair in 1935, says that more closely related taxas produce more similar chemical products. Beale and coworkers in 1940, surveyed 32 species of Tulip for anthocyanin contents and

distribution of group of compounds in genus as a taxonomic characters.

Conden et.al. in 1944, develop paper chromatography.

Bat & smith in 1948, showed that paper chromatography applied to analysis of plant

pigments.

Clasification of Chemotaxonomy: based on the taxonomical and chemical knowledge:

_ Descriptive taxonomy

_ Dynamic taxonomy

_ Serotaxonomy

Descriptive taxonomy deals with the classification of plant and secondary metabolite and

other products like sugar & amino acid. It is also concerned with evolutionary change,

chemical convergence and divergence in the plant.

Dyanamic taxonomy is based on biosynthetic pathway.

Serotaxonomy or semantics is based on pathway of specific proteins and amino acids

sequencing in proteins. It is further classified as;

1. DNA- primary semantics

2. RNA-secondary semantics

3. Proteins-tertiary semantics

Principle of chemotaxonomy

_ Chemical classification of plants is based on their chemical constitutions; i.e. on their

molecular characteristics.

_ The same type of metabolites can be the product of two quite different pathways.

_ Different plants sometimes contain secondary constituents belonging to different classes of

compound but biosynthetically appear to be same.

_ Chemotaxonomic studies include the investigation of the pattern of compound occurring in

the plant and preferentially in all various individual parts of plant such as the bark , wood,

leaves , root, cuticles and seed.

_ Such integrated investigations are necessary in order to obtain really convincing evidence

for the relationship of plants.

_ Before any important conclusions are drawn about the presence or absence of a particular

compound adequate sampling of a large number of members of the species at different stages

of development and growing in different environment should be made.

Different stages of Chemotaxonomic investigation:

1. Choice of group, taxonomic survey and sound sampling

2. Modification of suitable chemical techniques

3. Analysis of all material

4. Interpretation of data and its comparison from all other sources

According to the interest of investigation the relative stages may vary (for taxonomy,

phylogenetic & chemistry)

Sound sampling: an understanding of natural variation within a group and phylogenies are

helpful in good sampling. The collection of plant sample done:

_ By the help of professional plant collector

_ From national garden and national herbarium

_ From professional plant sellers

_ Personal travel & collection

Modification of suitable chemical techniques:

_ Depending upon the choice of investigator, what class of material is likely to exhibit useful

variation at the taxonomic level.

_ Intraspecific chemical variation

_ Qualitative and quantitative variation between different parts of same plant

_ Variation due to Seasonal and environmental fluctuation

Analysis of the material: qualitative and quantitative analysis is done by phytochemical

screening, electrophoresis, chromatography, finger print, and spectroscopy. All the spectra

obtained from different technique should be analyses.

Interpretation and comparison of data:

All the data obtained from chemistry, phylogenetic and taxonomy is interpreted & depending

upon the evidence the classification of plant should be reconsidered. If only a minor change

occurs in the match of chemical and other variation then the classification is essentially

confirmed.

Three broad categories of compounds are used in Chemotaxonomy:- .

1. Primary metabolites

2. Secondary metabolites,

3. Semantices.

Primary metabolites, are parts of vital metabolic pathways, most of them are of universal

occurrence and is utilized by the plant itself for growth and development. Example; starch,

chlorophyll, aleurone grain, citric acid, aconitic acid, etc.

CARBOHYDRATES IN CHEMOTAXONOMY:

Carbohydrates are universal constituents of living organism and widely distributed in the

plant. Thus, carbohydrate is having little chemotaxonomic significance, but some of the rare

sugars having chemotaxonomic significance.

Eg.

6-Deoxy hexose;

2, 6-Dideoxy hexose;

Gentiobiose & Gentianose;

Polyols and polysaccharides,

6-Deoxy hexose: It occurs in the form of methyl ether that is restricted to certain family.

So the presence or absence of such sugars is help in the study of phylogenetic relationship.

Ex. L-thevetose and D-digitalose are used as cardiotonic.

2, 6-Dideoxy hexose: Cardinolides containing D-digitoxose, L-oleandrose, D-cyamarose

sugars are particularly abundant in family apocynaceae and asclepiadaceae (both are group of

unrelated family).

Gentiobiose and gentianose: These are uncommon sugar in amygdalin, characteristic of

family rosaceae and gentianaceae respectively.

Polyols: Among monosaccharide derivatives eg. D-sorbitol, D-mannitol and mesoxylitol;

D-sorbitol occurs naturally in fruits of various rosaceae family. The presence or absence of

these sugar alcohol in rosaceae can be utilized to identify subfamily.

It is reported that sorbitol is present in all species belong to subfamily of rosaceae like

spiraeoidae, pomoidae, prunoidae, and rosoidae, but in species of ulmaria genus belong to

rosoidae, sorbitol is absent. So, the absence of this chemotaxonomy marker confirms the

removal of ulmaria from spiraeoidae to rosoidae.

Polysaccharides: It is condensation of large number of monosaccharide molecules.

That is universal in the energy storage forms eg. Starch, dextran, fructan, cellulose, and

inulin. Among these polysaccharides inulin is characteristic of family compositae, while the

fructan is present in family graminae. Thus, polysaccharide is also utilized in confirming

phylogenetic relationship. Eg. Tropical and subtropical species of grasses accumulate starch

in their leaves, while temperate grasses accumulate fructans.

Secondary metabolites present in plant, is used for protection and defence. Eg. Glycoside,

alkaloid, volatile oil, flavonoid and plant phenol.

Glycosides in chemotaxonomy:

Glycosides are compounds in which one or more sugars are combined with non-sugar

components by glycosidic linkage or by hemiacetal linkage involving oxygen (Oglycoside).

_ Depending upon the linkage the glycoside may be classified as:

O-glycoside; eg. Rhein.

C-glycoside; eg. Aloin, cascaroside.

N-glycoside; eg. Adenosine.

S-glycoside; eg. Sinigrine.

_ Distribution of O-glycosides is widespread, so it is having little chemotaxonomic

value.

_ The nature of sugar moiety and its position of attachment to aglycone maybe characteristics

of cardiac glycosides. Eg. L-thevetose, D-digitalose, Dcymarose,

L-oleandrose (cardiotonic)

_ C-glycosides, which possess a direct carbon linkage between sugar and non-sugar are rare

in nature. They are found in some plants containing anthraquinone derivatives eg. Aloin in

aloe-liliaceae; cascaroside in cascara-rhamnaceae.

_ About 25 C-glycosides of flavonoid group are known more are flavone and few iso-flavone

and flavanone, these are plant phenol, but studied in C-glycosides.

_ S-glycosides are examplified by those produce isothiocyanate on hydrolysis.

These compounds are characteristic of the family cruciferae, moringaceae, capparaceae. So

these family having phylogenetic relationship.

Cyanogenetic glycoside in chemotaxonomy: _ Plant species having ability to produce hydrogen cyanide by enzymatic hydrolysis are

common in family Rosaceae, Passifloraceae, Leguminosae, Gramineae.

_ Different amino acid like phenyl alanine, tyrosine, valine, leucine, and isoleucine are

precursor for the biosynthesis of cyanogenetic glycosides, but they are restricted to particular

family. Example: Leucine-Leguminosae and sapindaceae.

_ On the basis of amino acid precursors some conclusion may be derived, at family level

cyanogenetic glycoside amygdaline synthesized from phenyl alanine, restricted rosaceae, but

same compound synthesized from amino acid valine or isoleucine is restricted to

Leguminosae. The accumulation of cyanogenetic glycoside is also significant in confirming

the position of certain family.

Thioglucoside in chemotaxonomy:

_ These are responsible for the characteristic flavors of various plants or family brassicaceae

and few related family like, Capparidaceae, Tropaeolaceae and Resedaceae.

_ On the basis of alkyl component of glucosinolate compound, brassica species can be

differentiated eg. Brassica juncea (mustard) from Indian subcontinent contain

3-butenyl glucosinate and allyl glucosinate while those from Asiatic country contain only

allyl compound. So ancestry of Indian species is doubtful, because that is hybrid of B. nigra

(allyl glucosinate) and B. compestris (3-butenyl glucosinate).

ALKALOID IN CHEMOTAXONOMY

_ Alkaloids are compounds, containing heterocyclic nitrogen, basic character and complex

molecular structure. Such compounds are restricted to plant kingdom.

o True alkaloids have a nitrogen-containing nucleus derived from biogenetic amine.

o Proto alkaloids derived from amino acids, but lack a heterocyclic ring.

Natural protoalkaloids are usually simple amines e.g. ephedrine , mescaline.Some times they

may be precursor of true alkaloids.

o Pseudo alkaloids biologically unrelated to amino acids.Most of them derived from-

terpenes, sterols , nicotinic acid or purines.

Plant Phenol in chemotaxonomy:

_ Most commonly occurred phenolic compound is mono or Dihydroxy derivatives of benzoic

and cinnamic acid. Phenolic compounds having restricted occurrence may have

chemotaxonomic value eg; Trihydroxy derivatives of benzoic acid and cinnamic acid.

_ Eg: Ellagic acid is absent in fern, gymnosperm and monocotyledon, but it is infrequently

found in dicotyledon family. It is useful chemotaxonomic marker in subfamily rosoidae

(tribe-kerrieae)-rosaceae.

_ 4-hydroxy benzoic acid and 4-hydroxy phenyl acetic acid have been reported in eight

genera of family saxifragaceae, but in case of Astilbe genus, 4-hydroxy phenyl acetic acid is

replaced by 2-hydroxy phenyl acetic acid.

_ Coumarin derivatives are common volatile constituent responsible for odour in many

plants. The hydroxylated derivative are having restricted distribution can be utilized as

chemotaxonomic marker eg. Umbelliferone occurs widely in Umbelliferae while in

Compositae it is characteristic of genus Hieracium (hawkweed).

_ Flavonoids are largest group of phenolic compounds. They are mostly found in the vacuole

of higher plant and absent in lower plant.

Different classes of flavanoids:

Flavones

Flavanone

Isoflavanone

Isoflavonoids

Anthocyanidin

Chalcone

_ All flavonoids have common biosynthetic origin and therefore it posses the same basic

structural element, e.g. 2-phenylchromone skeleton. They may be present in many classes

depending on degree of oxidation of pyran ring which may be open and cyclize into furan

ring, e.g. 2-phenyl benzo pyrilium: anthocyanin & 2-phenyl chromone: flavone, flavanol,

isoflavone.

_ Flavone & flavanols and their glycosides are universally distributed but some of the

substitution patterns are restricted to certain family, having chemotaxonomic importance.

E.g. 6-o-substituted flavonoids in family: Laminaceae,Rutaceae, Asteraceae.

5-deoxy flavone in family: Fabaceae

2-o-substitueted flavonols in family: Laminaceae, Solanaceae.

_ Anthocyanidins, water soluble pigments responsible for red, pink, purple, blue,violet

colours to flower and fruit.these pigments occurs as glycoside anthocynidins and their

aglycones anthocyanidins. These are rare in gymnosperm but mostly occurs in angiosperm.

Except in Caryophyllales.