Classification of Plant Drugs • Alphabetical • Taxonomic • Morphological • Pharmacological/Therapeutic • Chemical/Biogenic
Alphabetical Classification • Latin/vernacular names • Advantage: quick reference • Disadvantage: no indication of the interrelationships between plants (drugs) • Used in • Dictionaries • Pharmacopoeias
Taxonomic Classification • Plants classified based on their botanical classification • (Plant) Drugs are arranged according to the plants they are derived from (class, order, family, genera & species). • Advantage: Precise & ordered arrangement (no ambiguity) • Disadvantage: Botanical knowledge decreases over the years in students • < popular with teaching
Morphological Classifications • (Plant) Drugs are divided into organized and unorganized drugs • Based on plant morphology • Advantage • Practical application to the study of plant drugs • Disadvantage • Microscopical studies are needed to identify powdered herbs
Organized drugs Leaves Flowers Fruits Seeds Herbs Whole organisms Woods Barks Rhizomes Roots Unorganized drugs Dried latices Extracts Gums Resins Oils Fats waxes Morphological Classification
Pharmacological/Therapeutic Classification • Plant drugs are grouped according to their pharmacological action of the most important active constituent in the plant • OR • According to the drug’s therapeutic use • Disadvantage: The constituents of one drug may have more than one therapeutic action (fall into numerous groups. E.g. Flavonoids)
Biogenic/Chemical Classification • Drugs are classified according to the main active chemical constituent available in the plant • OR • The biosynthetic pathways of the main active constituent. • Advantage: Popular for teaching when Pharmacognacy is phytochemically based. • Disadvantage: Ambiguities: Plants contain more than one group of active constituents each with different actions
Cultivation, Collection & Preparation of Crude Drugs • Crude drugs cultivated or uncultured plants • Some cases: pharmacopoeias specify cultivated spp. Such as Fennel, ginger, cinnamon & opium • Opium: only official growers may legally produce herbs. • Other herbs: senna, tragacanth etc, may be collected from wild or cultivated species.
Disadvantages of Wild plant Collection • Sparse distribution e.g. Sceletium tortuosum • Potentially difficult to transport herb to area of processing • Difficult access (e.g. Forests, Mountains etc) • Collector ignorance admixture of other plants, collection of undesired plant parts or stage of development or during an incorrect season loss of medicinal activity. • Damage to natural environment Extinction of a spp.
Advantages of Cultivated Herbs • Only desired spp are collected uniform quality. • Collection, transport & access to processing facilities is improved. • Better control of soil quality, pests & plant disease. • Supply: Constant & Regular (Controlled) • Herb collectors - trained
Plant Variation • Ideally: correct cultivation & harvesting is aimed at producing high quality, healthy herbs. • Complicated: All natural products: variation between individual plants. • Plant size • Content of medicinal actives • WHAT BRINGS ABOUT THIS VARIATION?
Variation Factors • 3 Groups • Environmental (Exogenous) Factors • Genetic (Endogenous) Factors • Post-Cultivation Factors (Drying & Storage Methods etc)
Exogenous Factors • Climate • Altitude/Latitude • Collection Season • Soil Condition • Developmental Stage of the Plant • Plant Condition • Use of Growth-Promoting Substances • Allelopathy • Parasites
Effect of Climate • Plants should be cultivated in conditions which are similar to the plant’s natural habitat • Most herbs grow best in sunny, dry conditions • Factors affecting climate • Temperature • Rainfall • Day-length
Temperature • Major component • Affects both the growth/development • AND • Metabolism of the plant • Each plant is specialized to adapt to its native environment • But most are able to exist in wide temperature ranges. • E.g. Tropical & Sub-tropical plants in temperate regions
Temperature: affects plant chemical Reaction Rates E.g. Datura stramonium: lower alkaloids in cloudy/rainy weather (winter). • E.g. Volatile oils are produced more readily in warmer weather, yet very hot days lead to a physical loss of oil • Growing peppermint in shade rather than the sun.
Rainfall • Consider: annual rainfall, distribution, humidity effect, soil type. Especially NB for the production of volatile oils • May influence the production of glandular hairs • Continuous rainfall: loss/leaching of water-soluble substances through leaves & roots: glycosides, tannins & flavonoids & some volatile oils. • NB: over-watering
Day-length • Amount & intensity of light needed differs from herb-herb. Affects the amount of glycosides, alkaloids & volatile oils produced. • E.g. peppermint: • Long day: menthone, menthol & menthofuran traces • Short day: menthofuran = main component • Other spp: produce more active constituents at night • E.g. Nicotaina • Flowers: only produced under x day-lengths (NB where seeds are used medicinally).
Radiation • Type of radiation plants receive = NB • E.g. Ocimum basilicum – plants grown in glass houses have less phenols & terpenoids in the leaves (flavonoids, volatile oils). • E.g. Tomato
Latitude & Altitude • Gentian: bitter constituents increase with altitude • Thyme & Peppermint: constituents decrease with altitude • Other oil producing plants reach a maximum at x altitudes. • Flower production is also affected by location (altitude) • Fat/oil production may be influenced by latitudes. • E.g. Peanut & olive trees grown in the subtropics have a higher unsaturated fat content.
Collection Season • Active constituents of herbs are affected by the seasons (due to climate, rainfall, day-length etc). • Medicinal plants should be therefore collected in the season in which their active constituents are highest. • E.g. Rhubarb (laxative) contains high anthranol in winter. This is then oxidized to anthroquinones in summer.
Soil Condition • Soil character, composition, permeability, porosity all effect the health of medicinal herbs. • E.g. Chalky soil poor Digitalis growth • Nutrient content of soils crop rotation • N2 – nitrates • Phosphate – bone • Potassium – wood ash • Ca – lime/egg shells • pH of soil affects inorganic compounds of soil
Developmental Age of Herb • Different components are produced in varying amounts at different developmental stages • Vitamin C Highest in rosehips just before maturity • Camphor accumulates therefore collected from older trees • Alkaloids highest in young seeds • Young cloves higher oil content than older cloves
Herb Condition/Parasites • Certain other factors also influence the quality of the herb. • E.g. Fungus on henbane lowers the alkaloid content • It is therefore necessary to control pests and disease which may affect herbs and their medicinal value • Only possible when herbs are cultivated
Use of Growth-Promoting Substances • Auxins • Gibberellins • Cytokinins
EFFECTS Cell elongation Increase in stem length Promotion of adventitious root growth Fruit setting in the absence of pollination USES [low] Accelerate the rooting of woody cuttings E.g. Trees raised from cuttings instead of seeds [high] Acts as a selective herbicide or weed-killer Auxins
Gibberellins • Isolated from a Japanese rice fungus • Uses: initiates the synthesis of enzymes needed for seed germination & seedling establishment.
Cytokinins • Uses • Play an important role in cell division • Promote protein synthesis • Involved in bud differentiation
Allelopathy • Definition: The constant effect which living organisms exert on each other, which may be either beneficial or harmful. • In Plants: different plants growing together affect factors such as • Germination rate • Leaf development • Fruit maturation • Chemical constituents produced
Allelopathy Effects • Transmitted between plants in a number of ways • Exhalation of leaves • Root secretions • Extractions from fallen leaves into the soil • Mutual dependant organisms (beneficial) symbiosis • E.g. Urtica dioica (stinging nettle) • Destructive allelopathy antibiosis • E.g. Belladonna growth inhibited when cultivated next to mustard
Other factors • Effects of Exogenous factors may affect plants growing in isolation differently than plants growing in communities • E.g. Camphor trees: produce > camphor when growing alone than those growing in groups. • Ergot: alkaloid content differs according to the host (specific rye spp or other type of cereal e.g. barley or oats) • Variation of actives • E.g. Foxglove produces more actives during the day than at night.
Endogenous Factors • Genetic differences are responsible for • Morphological variety • Biochemical diversity (amount & type of chemicals produced) • Chemical races
Polyploidy • Somatic number: no. of chromosomes present in the plant cell nucleus. • normally the same for all tissues of the same plant. • normally an even number Possible to divide the chromosomes into pairs • Each member of the pair identical • Termed: Diploid • In some plants: chromosomes ≠ diploid • = triploid, tetraploid, otaploid • = Polyploid plants
Polyploidy • Naturally occurring polyploidy • Mentha • Commercial crops (wheat, oats, cotton) • Artificially induced • Heat treated • Addition of Specific chemical agents • Effects: variety of changes • Plant size • Organ size • Individual cell size • Change in chemical constituent production
BENEFICIAL Deadly nightshade (Atropa belladonna) X2 alkaloid than diploid Papaver somniferum (opium poppy) latex x2 morphine than diploid Carum carvi (carraway) yields > volatile oils than diploid NON-BENEFICIAL (Potential) Reduced growth Reduced plant vigour Reduced plant fertility Effects of Polyploidy
Plant Breeding Methods • Influence morphological and chemical variety in plants • Aimed at reducing variability of these factors (naturally produced by genetic differences) • At producing plants with constant, desirable characteristcs. • 3 methods • Selection • Hybridization • Transgenic medicinal plants
Selective Breeding Individual plants showing the most desirable characteristics are chosen and interbred 2nd population: improved quality Reason: even in a single species of plants appearing identical, genetic varieties are present making them slightly different from each other Result: improved growth rate disease resistance winter hardiness increased yield of medicinal actives
Hybridisation • Mating of different spp or varieties to produce a hybrid progeny, different from both parents (incorporating desired characteristics). • E.g. Mentha piperita & M. spicata are naturally occuring hybrids.
Transgenic Medicinal Plants • Genetic Engineering: Recombinant DNA • Transfer DNA sequences from the chromosomes of 1 plant to another • Lead to the artificial transfer of a particular character from one organism to another
SEED E.g. Digitalis Rx of seed prior to sowing may influence germination X plants need soaking before germination (H20/acid) VEGETATIVELY E.g. Bulb, tuber, rhizome By division: plant separated from aerial stems/buds, each with roots & growing point Runners: mint Stolons: Liquorice Cuttings Grafting Fermentation Inoculation Cell culture Plant Propagation
Harvesting of Herbs • Roots & Rhizomes: collected when aerial parts are dried down (if not – fleshy & difficult to dry) • Bark: Damp weather • Aerial parts – at flowering (active photosynthesis) • Flowers e.g. clove – before fully expanded • Fruits – vary • Fully ripe: Anise, Fennel • Nearly ripe: cardamoms (Before seed dispersal) • Gums/Resins – dry weather
Preparation of Herbs • Remove sand, stones • Washing underground parts • Remove rootlets, diseased portions • Slicing – larger organs (ginger) • Peeling – ginger/liqourice • Removal (e.g nux vormica – fruit pulp) • Packing into quills (cinnamon) • Grading (senna, gums)
Drying of Crude Drugs • Aim = removal of excessive moisture • Ensures good keeping • Prevent mould & bacterial growth • Prevent enzyme activity preventing chemical changes • Ideally: herbs should be dried ASAP after collection (maintains appearance & chemical activity)
Drying Methods • Air Drying • Artificial Drying • Vacuum Drying
Air Drying • Sun Drying • When herbs are not adversely affected by excessive sunlight. • Dried in thin layers tuned over occasionally • E.g. clove, cardamom • Shade Drying • When sunlight causes discoloration & warping/shrivelling • E.g. cinnamon
Artificial Drying • Generally the most acceptable form of drying herbs. • Rapid (less exposure to heat less chances of chemical alteration) • Control temperature (normally 40ºC) & ventilation (allows dry air to replace wet air).
Vacuum Drying • Steam-heated ovens: pump used to extract air • Low pressure to ensure rapid and complete drying • Expensive method • Reserved for expensive herbs and which cannot be sufficiently dried through other methods.
General Drying Techniques: Leaves • Leaves/Herbs: • 40-50º C • Maintains good colour • Without overdrying herbs • Normally destalked first • Best dried for short periods of time only prevents shrivelling and discolouration • Leaves may be bleached through the drying process best dried in dark
General Drying Techniques: Roots/Rhizomes • Washed • Sliced • Dried between 30-65ºC • Temperature too high: forms a tough crust on the outside preventing the further drying of deeper tissue • Thick organs may require long periods of drying (10days-3weeks) to avoid mould growth.
General Drying Techniques:Flowers • Normally destalked before drying • Flowers may also be bleached when dried best dried in dark.