Plant Secondary Metabolites PDF

Plant Secondary Metabolites 1 2 3 Phenolics 4 Phenolics 5 6 PHENOLICS 7 1. Coumarin Simple phenolic compounds, widespread in vascular plants and appear to function in different capacities in various plant defence mech...

Plant Secondary Metabolites 1 2 3 Phenolics 4 Phenolics 5 6 PHENOLICS 7 1. Coumarin Simple phenolic compounds, widespread in vascular plants and appear to function in different capacities in various plant defence mechanisms against insect herbivores and fungi. Derived from Shikimic acid pathway. Cyclic compounds behave as natural pesticidal defense compounds for plants. Scopoletin Dicoumarol 8 9 2. Lignin After cellulose, the most abundant organic substance in plants is lignin. Highly branched polymer of phenyl-propanoid groups. Physical toughness deters feeding by herbivorous animals and its chemical durability makes it relatively indigestible to herbivores and insects. 10 3. Flavonoids  Perform very different functions in plant system including pigmentation and defence.  Plant phenols constitute one of the most common and widespread group of defensive compounds, which play a major role in HPR against herbivores, Including insects 11 12 13 14 15 4. Isoflavonoids (isoflavonones)  Isoflavonoids are derived from a flavonone intermediate, naringenin.  play a critical role in plant developmental and defence response.  Secreted by the legumes and play an important role in promoting the formation of nitrogen fixing nodules by symbiotic rhizobia.  Rotenoids  Clover  phytoelexins 16 5. Tanins  It included under the second category of plant phenolic polymers with defensive properties.  Tannins are general toxins that significantly reduce the growth and survivorship of many herbivores and also act as feeding repellents to a great diversity of animals.  Tanning-- hide  leather 17 18 19 20 Anthocyanidins Increase vitamin c level Protect against free radical damage 21 Flavones and Flavonols 22  Flavonols myricetin, quercetin, isorhamnetin, kaempferol, isorhamnetin. Myricetin has anti-inflammatory and anti-cancer effects. Quercetin, the main flavonoid in the diet, may lower risk for asthma, heart disease, and lung cancer. Best sources for myricetin: berries, grapes, parsley, spinach. Best sources for quercetin: onions, apples, broccoli, cranberries, grapes. Catechins and gallic acid Catechins and epicatechins may lower the risk of coronary heart disease, some types of cancers and promote healthy lungs. Best sources for catechins: tea, red wine, cocoa powder, dark chocolate, grapes, plums. Best sources for epicatechins: teas, fruits and legumes (beans). 23 Flavanones Hesperetin, naringenin, eriodictyol. Hesperetin found in grapefruits and oranges is one candidate that may benefit the cardiovascular system (atherothrombotic diseases, and lower the levels of LDL cholesterol. Naringenin has antioxidant, antiestrogen, and cholesterol-lowering properties. Best sources for hesperetin and naringenin : citrus fruits and juices. 24 Plant secondary metabolites as natural products: terpenes and terpenoids (~25,000 types, 55%), alkaloids (~12,000 types, 27%), and phenolic compounds (~8,000 types, 18%). In bio-pesticide market, the most important is pyrethrum followed by neem, rotenone and essential oil. In USA, it is registered for being use in agricultural, residential, commercial, industrial, and public health sites. Typically used as insecticides (e.g., Pyrethrum, rotenone, rape seed oil, quassia extract, neem oil, nicotine) Repellents e.g. Citronella, fungicides e.g., Laminarine, fennel oil, lecithine, herbicides 25 Review: Types of Secondary Metabolic Compounds 26 Types of Secondary Metabolic Compounds 27 Roles of Secondary Compounds in Plant Biology 28  Secondary Compounds attract pollinators Magnolia Aristolochia, “pipevine” Aquilegia, “columbine” Pollinators are attracted by floral shape, color, scent. Pollinators are rewarded with nectar (sugars) or other essential nutrients (amino acids, volatiles). Some flowers are generalist, while others have highly modified forms adapted to specific pollinators. -Specialist flowers have co-evolved with effective pollinators. Calochortus leichtlinii, “Mariposa lily” Secondary Compounds (phenolics, terpenoids) 29 involved.  Secondary compounds in flowers Flower color and smell is often the product of phenolic compounds like anthocyanins 30 Secondary compounds: chemical adaptations for biotic dispersal of seeds Attractive colors, scents, rewards (sugars/nutrients) Often combined with thick/hard seed coats or other structures to protect embryos from chomping teeth (i.e., the peach pit protects the seed inside) seeds may be dropped away from the parent plant either before or after passing through the animal… Seed dispersal is important: - removes offspring from competition with parent. - potentially introduces plant species to new areas, expands range. - plants that disperse widely safer from local extinction? Biotic seed dispersal is potentially less random than abiotic. 31  Secondary Compounds and dispersal Fruits are brightly colored to attract birds or mammals – Phenolic pigments (flavonoids, anthocyanins) When seeds are developing – Fruit is not as palatable and lacks color (= green) – Unripe fruit may contain secondary compounds to deter feeding. – Change in taste and color (ripening) occur when seeds are ready to be dispersed. Fruits may contain compounds that deter insects, but are still edible for birds and mammals 32  Plant/Animal arms race? Cretaceous Period: Dinosaurs have developed strategies to deal with protective plant surfaces – Teeth adapted for grinding tough leaves – evolved gizzards, swallowed stones to help disrupt plant tissue Fraenkel 1959 – Article in Science suggests secondary compounds arose as a means for plant defense – As with physical features, we see evolution of many different secondary compounds with defensive roles, as well as convergent evolution of biosynthetic pathways to create similar secondary compounds in different plants. 33 secondary Compounds in Plant Defense Plants produce secondary compounds to reduce grazing – Predators include bacteria, fungi, insects, mammals Secondary compounds work due to a variety of characteristics – Bad taste or smell (repellent effectd/deterrents) – Physiological effect (toxins) Insects, in particular, have co-evolved their own counterdefenses against the plant compounds 34  Defensive secondary compounds Grazers avoid coca plant (cocaine) and coffee leaves (caffeine) due to the presence of toxic alkaloid compounds. Glycoalkaloids penetrate cell membranes of skin cells on mouth and tongue and break down tissues lining mouth and stomach – Sprouted potatoes (Solanum tuberosum) – Unripe tomatoes (Lycopersicon esculentum) – Woody nightshade (Solanum dulcamara) Glucosinolates (secondary organic compounds containing nitrogen and sulfur) give some vegetables (cabbage, brussels sprouts) their strong flavor. 35  Glycoalkaloids Glycoalkaloids = alkaloid with sugar molecules attached. -Produced in tubers when exposed to light – natural defense against herbivores. Chlorophyll content also increases (=> greening of the potato), but bitter taste indicates solanine buildup. - Disrupts cellular ion balance, leads to cell death. Symptoms include vomiting, diarrhea in vertebrates. 36 More anti-insect strategies and communication (!) Solanum tuberosum: the potato In addition to alkaloid production, leaves damaged by insects increase their production of protease inhibitors – These disrupt the insect’s digestion and development Damaged leaves also send chemical messages to other leaves and ‘tell them’ to do the same 37  Terpenes as signals for insect parasites Plants emit volatile terpenes that attract the heribivore’s enemies Zea mays (maize) is damaged by butterfly larvae 1. Plant emits terpenes that attract parasitic wasps 2. Wasps lay eggs on larvae 3. Only occurs when plant is damaged by larvae 38 Monarch Butterflies and Cardiac Glycosides 39 Naïve bluejay experiments Birds that eat monarch butterflies become violently ill. Young birds quickly learn to recognize Monarchs, and won’t eat them. 40 Mimicry Viceroy butterfly mimics the Monarch butterfly Birds avoid the viceroy even though it does not contain terpenoid cardiac glycosides 41 Drugs from plants 42  glucosinolates (mustard oil glycosides) – Brassicaceae and other related families – garden nasturtium Tropaeolum – condiments: mustard, horseradish – anti-cancer effects of Brassica – antibiotic effects – but also anti-thyroid effects – livestock poisoning 43  disulphides – onions, garlic, & other Allium species – includes "lacrimatory factor" – antimicrobial effects – reduce blood clotting 44 Asafoetida Ferula assa-foetida (Ferula foetida) – Apiaceac HING, Merde du Diable (Fr), Devil's Dung – Used in Indian cuisine – Oleo-gum-resin – disulfides 45 46  Glycosides Composed of glycone + aglycone – Sugar part + active portion Active once hydrolysed (broken down) Some require specialized bacteria in large intestine to hydrolyse them and release the active portion Some kinds are toxic: – Cyanogenic glycosides (releases cyanide) – Cardiac glycosides (affect rhythm and strength of heartbeats) 47 48 49