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Plant Metabolites & Ergastic Cell Contents Primary Metabolites Primary metabolites Fx: Important roles chlorophyll in growth and AA’s development Nucleotides photosynthesis Simple CHO’s respiration Membrane lipids solute transport translocation nutrient assimilation *** ARE FOUND differentiation THROUGHOUT THE PLANT KINGDOM Secondary Metabolites Definition: Differ from 1º metabolites All organic compounds in that they have a Have no direct function restricted distribution in the plant kingdom in growth and development Therefore: Only Also called secondary particular secondary metabolites are found products or natural products in only one specific plant species or a taxonomically related group of species. Secondary Metabolite Fx be functionless end Initially thought to products of metabolism or metabolic waste products Responsible for characteristics, odours, pungencies & colours of plants. Others give plants their medicinal, culinary or poisonous values. They are synthesized to aid the producing plant’s survival. Secondary Metabolite Function Ecological functions in plants: protect against herbivory Protect against infection by microbial pathogens Attract pollinators & seed distributing animals Act as agents for plant-plant competition Evolution of 2º Metabolites 2º Metabolites evolved through mutations in the basic metabolic pathways appearance of new compounds happened to be toxic or a deterrent to herbivores and pathogens • As long as they were not toxic to the plant itself and were produced at a low metabolic cost They gave the plants containing them greater reproduction fitness than undefended plants (plant- plant competition) Undefended plants therefore left more descendants while the protected plants left less And passed their defensive traits on to the next generation The defence compounds (secondary metabolites) that increase reproductive fitness of plants by warding off fungi, bacteria and herbivores, also make them undesirable as food by humans. Many NB crop plants have been artificially selected for producing relatively low levels of these compounds, which make them more susceptible to insects and disease (e.g. of Wheat) 3 MAIN GROUPS OF 2º METABOLITES TERPENES PHENOLS N2-CONTAINING COMPOUNDS Terpenes Terpenes are lipids synthesized from acetyl CoA or from the basic intermediates of glycosides Phenolic compounds Phenolic compounds are aromatic substances Formed via the Shikimic acid Pathway or the Malonic acid pathway Nitrogen-containing compounds e.g. alkaloids synthesized from AA’s Active Plant Constituents Carbohydrates Sugars (glucose, xylose) Starches (energy stores) Cellulose (structural support) Gums & mucilage Gums & Mucilages Very complex CHO’s Found in excellent vulnerary, demulcent & emollient herbs. E.g. Marshmallow & Plantain Gums & Mucilage Fx Relax Gut lining Relax Respiratory System Reduce irritation and inflammation (GIT, Respiratory, US) MO: soak up large amounts of water sticky jelly: dry irritated skin, inflamed/painful tissues Some stimulate immune system: e.g. Acemannan (Aloe vera) Plant Alcohols Occurs in plants in various forms Constituent of volatile oils & sterols Attar of Rose Menthol in peppermint Waxes (beeswax) Cutins Phenols Phenol = basic building block for many plant constituents Simple/complex in nature Fx: anti-inflammatory Anti-septic E.g. Salicylic acid (Willow) Eugenol (Clove) Thymol (Thyme) Volatile Oil Function Anti-spetic (Garlic/Thyme oil) Stimulate tissue irritation e.g. Mustard numbing e.g. Camphor oil). Aid digestion CNS action Insect repellent Anti-inflammatory Anti-allergenic Proanthrocyanins Closely related to tannins & flavonoids Phenols Fx: powerful anti- oxidants Protect circulation from damage: especially circulation of the heart, hands, feet & eyes. E.g. Crataegus spp. Tannins Fx – give herbs their astringent & heamostypic action Act on proteins and form a protective layer on the skin & mucous membranes Bind the tissues of the gut Reduce diarrhoea & internal bleeding Externally: Rxing burns, sealing wounds & reducing inflammation. Heal infections of the eye, mouth, vagina, cervix & rectum (mucous membrane tissues) Tannins - phenols Coumarins (smell of cut grass) Limited effects on the body Di-coumarol, (metabolite) powerful anti-clotting agent. Functions: Allopathic: Basis for warfarin (thrombosis in small doses): Horse Chestnut (Rat poison in large doses) Visnaga – powerful smooth muscle relaxant Anthraquinones Plants containing anthraquinones effective purgatives (& good natural dyes) Senna & Aloe Also make stool more liquid (Constipation) Fx: gently stimulate colon 8-12 hrs after ingestion (stimulate peristalsis) Can only Fx when natural bile is present. Tend to cause colonic pain (over-stimulate colon wall) Glycosides Flavonoids Saponins Phenolic glycosides Cardiac Glycosides Cyanogenic Glycosides Flavonoids One of the most common group of plant constituents Polyphenols Wide range of actions Anti-spasmoidic Anti-inflammatory Anti-oxidant Diuretic Circulatory Stimulants Cardiac stimulants Anti-viral hepatic Saponins Pharmaceutical Chemists synthesis of cortisone (anti-inflammatory) & sex hormones Saponins in herbs do not act in the same way body can use them as building blocks to form appropriate chemicals. Fx: anti-inflammatory Expectorant Aid nutrient absorption Cardiac Glycosides Discovered from Foxglove (1785) recognised to support a failing heart Many flowering plants contain cardiac glycosides Fx: increase heart efficiency Steady tachycardia NO CARDIAC STRAIN Strong diuretic Cyanogenic Glycosides Based on cyanide (toxic) Small doses Sedative Relaxant effect on heart & muscle Wild cherry bark: suppress & soothe dry, irritating coughs. Fruit kernels (apricot) Bitter Principles Group of chemicals with an exceedingly bitter taste Wide diversity of structure Most belong to the iridoids, some to terpenes Fx: stimulate digestive juices & appetite Aid the liver Anti-biotic Anti-fungal Anti-tumour Play specific roles depending on herb & chemical combination e.g. Valerian & Devil’s claw Alkaloids The most potent group of plant constituents Effect: body & mind Some: effect on lungs, liver, nerves, GIT Fx in plant: ± source of excessive N2. (makes them pharmacologically active). Divided into 13 groups based on their chemical structure (no general effects) E.g. Atropine (Atropa belladonna) reduce spasms, relieve pain & dry up bodily secretions Glucosilinates Found exclusively in the Brassica Family (Mustard & Cabbage) Instant blistering & inflammatory effect on the skin Applied to painful areas to increase blood flow Helps remove excessive waste products Eating: produce a strong pungent taste. Vitamins Found in many medicinal plants Lemon peel: Vitamin C Carrot: Vitamin A Brewers Yeast: B- vitamins Nasturium/watercress: Vitamin E Minerals Plants draw minerals from the soil and convert them into a form which is easily absorbed & used by the body. Kelp: I2 Dandelion: K Horsetail: Silica Nettle: Fe & Ca Brewers Yeast: Chromium CALCIUM OXALATE CRYSTALS Calcium Oxalate Numerous crystals occur in plants Ca-oxalate is one of the most common Like trichomes & stomata, it also has diagnostic value X polymorphs are characteristic in x plant spp. Crystal Systems In plants 2 crystal systems exist All crystal polymorphs belong to one of these systems Systems Tetragonal System Monoclinic System Systems differ in the amount of water they attain OD Tetragonal Crystal System Composition: CaC2O4.3H20 Arises from supersaturation of the cell sap with calcium oxalate Includes Prisms Cluster crystals (rosette aggregates) microsphenoids Monoclinic Crystal System Chemical composition: CaC2O4.H20 Form in the presence of excess oxalic acid Crystal forms include Some prisms Needle-like crystals (raphides) Sphaero-crystals NB!!! When using Calcium oxalate crystal types as a diagnostic tool: Crystal type Size Distribution Should all be noted. Crystal Function Uncertain More abundant in plants growing in arid regions. Ca: Causes epithelial cells to swell Deter herbivory? Crystal Forms Prisms Cluster Crystals Microsphenoids Raphides Sheaero-crystals Prisms – Elletaria cardamomum Found in Cardamom • Small single prisms • Starch masses in parenchyma Prisms – Hyosciamus niger Black henbane • Single prisms Some have a crystalline outgrowth (plug) • Twin prisms In crystal layer of spongy mesophyll cells (directly below palisade tissues) Prisms – Cassia senna Senna * Single prisms * Occurs in parenchyma cells * Surrounds bundles of pericyclic fibres * Forms a crystal sheath Prisms – Glycyrrhiza glabra Found in Liquorice * Single prisms * Occurs in parechyma tissue * Surrounds xylem & phloem * Forms an incomplete crystal sheath Prisms – Rhamnus purshianus Cascara senega Crystal sheaths Similar to liquorice Occurs with the phloem fibres Complete crystal sheaths Microsphenoids Atropa belladonna Aggregates occur in a crystal layer Below palisade tissues When a single cell contains an aggregate of microsphenoids idioblast Raphides Occur Singly • E.g. Ipecavanha In bundles • E.g Squill Diagnostic Value of Calcium Oxalate Crystals Absence of crystals Different form Different size all used to identify adulterants or allied species from medicinal herbs. Diagnostic Value of Calcium Oxalates E.g. Digitalis purpurea: (used medicinally) no calcium oxalates D. thapsi: (not used medicinally) - small prisms Diagnostic Value of Calcium Oxalate Crystals E.g. Atropa belladonna: Leaves have micro- sphenoids Phytolacca leaves: have raphides Diagnostic Value of Calcium Oxalate Crystals 3 Solanaceous Herbs Atropa belladonna • Microspenoids Datura stramonium • Cluster crystals Hyoscyamus nigra • Prisms LESSON TAKE-AWAY Definition & types/effects of adulteration Difference between 1º & 2º metabolites. E.g’s & Functions of metabolites Types of Ca-O crystals (E.g’s & Dx value) End of Lesson Thank You!
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