2024 BIO203 Lecture 9 Metabolic Diversity-1 PDF

1  Fall 2024 BIO203: Lecture 9 Don’t Eat Me: Plants Secondary Metabolites 2  Plant Metabolites Primary metabolites Secondary metabolites e.g. Carbohydrates,...

1  Fall 2024 BIO203: Lecture 9 Don’t Eat Me: Plants Secondary Metabolites 2  Plant Metabolites Primary metabolites Secondary metabolites e.g. Carbohydrates, Terpenes, Alkaloids, proteins, amino acids, lipids Phenolics Involve directly in the growth Produce for defense purpose 3  Plant Chemical Defenses, why are they Important? – Worldwide pre-harvest crop losses: 14% insects,12% disease, 10% weeds – Post-harvest losses include: Worms & insects feeding on seeds/storage organs Fungal & bacterial attack (e.g. Erwinia) – Secondary metabolites protect plants (e.g. our crops) Herbivores (e.g. insects & nematodes), pathogens (e.g. fungi, bacteria & viral) 4 Erwinia infected potato  Plant secondary metabolites, why are they Important? Carry out diverse ecological functions - attract pollinators, - modulate soil microbiota (Plant Growth Promoting Bacteria) 5 Plant metabolites, why are they Important? – Human uses: Therapeutic Drugs Pesticides, microbicides, herbicides & poisons Flavors Pigments & dyes Construction & fabrication Religious & cultural roles Perfumes & scents 6  Lecture overview Where do chemical defenses come from and how are they made – How are they grouped? What uses have humans put them to? What uses may humans put them to in future? 7  The defenses Plants are immobile, but not helpless An array of defenses – Constitutive = there all the time – Inducible = attacker is detected & a defensive response is mounted First line of defense against pathogens = waxy cuticle + cell walls (example of constitutive def.) Chemical defenses against herbivores often at least partly constitutive. 8  Secondary metabolites Some morphological defenses against Tomato glandular trichomes herbivores & insects (e.g. thorns) but most Defenses involve complex biochemistry Plants use >60,000 different secondary metabolites Up to 10% of the dry mass of a plant may constitute defensive chemicals Often stored in vacuole, some are secreted or presented in surface structures (often trichomes), or internal organs like resin ducts. Rob Schuurink UVA Netherlands 9  Secondary metabolites: 3 broad groups TERPENES ALKALOIDS PHENOLICS The only molecular structures you need to know (for the final) are those of the precursors! You will also need to 10 know about C & N use.  Terpenes TERPENES: >40,000 terpenes = 5C skeleton (isoprene) sub-unit 2,4,6, 8 linked as polymers – Smaller terpenes (5C- 10C) volatile & often released by epidermal gland cells as in flowers (perfumes) Example ‘evil’ terpenes Capsaicin & Resiniferatoxin Resin spurge 11  Terpenes Terpenes include essential oils found in herbs & spices – Give peppermint or basil their smells & aromatic substance in resin of conifers – Medicinal e.g. the sesquiterpene lactone Artemisinin (antimalarial). Also Ginseng! – Flavors e.g. Liquorice Volatility useful to: – Warn insects/herbivores of plant toxicity – Attract insect pollinators or herbivores to eat fruits Terpenes also include allelopathic agents, insecticides & anti-herbivore agents 12 Citrus secretory cavities Gymnosperm resin ducts  Terpenes: Carotenoids Carotenoids = 40C terpenes e.g. – Lycopene which gives tomato its red color & beta-carotenes color many fruits & vegetables (highest levels in carrot). Carotenoids useful as: – Antioxidants: ring structures absorb high energy electrons – Beta-carotenes used to synthesize Vitamin A Lycopene: Proven efficacy in preventing stroke and some cancers 13  Alkaloids >12,000 types Amino acid precursors Synthesized from amino acids tryptophan, tyrosine, phenylalanine, lysine & arginine – All contain Nitrogen Target Nervous System. Used medicinally as stimulants & sedatives e.g. – Codeine & morphine from opium poppy 14 15  Alkaloids Example alkaloids: – Codeine & Morphine from Opium Poppy – Atropine & Scopolamine from Belladonna & Datura (eye surgeries, anti- parkinson) – Caffeine from Coffee (Neonatal apnea, pain relief, dermatitis) – Ephedrine from Ephedra (hypotension) – Quinine from Chincona spp (malaria) – Aconitine from Aconitum spp opium (analgesic, anti-inflammatory and cardiotonic) – Cocaine from Coca (Local anaesthetic) – Nicotine from Tobacco – Piperine from Black pepper – Berberine from Barberry 16  Alkaloids Many crops contain traces of very toxic alkaloids e.g. solanine in potato – Reduced from higher levels in wild relatives by human selection Nicotine is a very effective insecticide & more toxic (0.5–1.0 mg/k) than Strychnine. Nicotine production up-regulated by insect attack & grazing Caffeine kills the larvae of the tobacco hornworm by inhibiting an essential enzymatic reaction. Also allelopathic. 17  Phenolics >8000 compounds Phenyl ring of 6C & a 3C Tail – Often OH group (phenolics) Derived from phenylalanine (or tyrosine) through loss NH2 group – Same precursors as some alkaloids but no N2 Plant use summary: – Structural, defense & protection, pigments, attractants, UV Human use summary: – Construction, antimicrobial/rot prevention, scents, pigments/dyes, flavors, medicine 18  Phenolics: Lignins Lignins are the prevalent phenolics – Component of cell walls/WOOD – Toxic to most microbes Lignin = complex polymer of phenol: strength, water proofing, protection from microbial degradation – 20-30% d/w vascular plants Wood tar Lignin often produced after pathogen attack or wounding (to seal up & protect exposed surfaces (structural & toxic) 19  Phenolics: Tannins Tannins (like lignins) are polymers of phenols Tannins react with proteins – Cross-linking. Less digestible – High tannin content deters herbivores. – Tannins often have an unpleasant taste Used by humans to process protein in animal skins to make it resistant to degradation by microbes – Tanning leather (E.g. using acorns) Some medicinal uses? e.g. anti- inflammatory, antiviral, antibacterial. 20  Phenolics: Flavonoids Flavonoids (~ 4,500 compounds) Give flowers their color as pigments Flavonoids often found inside plant cell vacuoles Some flavonoids also feeding deterrents and signaling molecules – E.g. legume-rhizobium signal released into soil from roots Lots of health claims: cancer, anti-inflammatory, heart health, antibacterial. No FDA- approved claims as yet Plant phenolics contribute to fragrances & flavors, E.g. vanillin 21  The future of plant secondary metabolites? Food crops bred for edibility and yield – Defense chemicals/natural product? – Flavor in modern ag/hort systems? – Nutritional value Dave Liscombe Vineland Research 22  Human health > 40% of the naturally occurring secondary metabolites so far tested can or may cause cancer in animal models. Some others may help prevent cancer E.g. Lycopene ‘Natural’ does not equal healthy… Herbal remedies may have serious side effects E.g. Echinacea carries elevated risk of spontaneous abortion Cyclopamine accumulates heavy metals is a ‘natural’ Non-pure active ingredient ingredient from Dose unpredictable corn lily Kidney problems 23  Human health 2/3 of our current drugs have a plant origin – New drugs continue to be identified in plants 24  Agriculture Historical pesticides have untested & unpredictable effects on human health & ecology Problems associated synthetics pesticides – Indiscriminate (non-pests/beneficial species killed) Sub-lethal effects also a big problem. E.g. Beehive collapse – Dangers to human health (chronic and acute) – Persistence (usually bigger problem for synthetic chemicals, although lignins can persist for >1000 years) – Break down products (particularly synthetics) e.g. DDT to DDE – Rapid resistance to chemicals applied in large quantities Biotech – Regulating or transferring secondary metabolite production 25  Want to know more? Michael Phillips – Metabolomics – Terpene metabolism – Mass spec. (GCMS system and LCMS/MS) BIO324H Plant Biochemistry BIO368 Medicinal Plants & Human Health 26  Biotic stress responses & 2ndary Metabolism: Key Points Plants represent a huge resource of fixed carbon, nutrients & complex molecules for anything that can access it Plants are immobile, but have an array of defenses (know examples) – Constitutive = There all the time – Inducible = Attacker is detected & a defensive response is mounted Pathogens get past cuticle & cell wall through wounds, Stomates, digestive enzymes or penetration structures Most plant defenses against attackers involve complex biochemistry = >60,000 different secondary metabolites – Often competitive or non-competitive inhibition of enzymes Secondary metabolites: 3 broad groups: terpenes, alkaloids (contain N) & phenolics subunit precursors: terpenes = Isoprene 5C, alkaloids & phenolics = amino acids – Know broad sub-categories Impacts of 2ndary metabolites on human health, medicine, food preferences, and crop selective breeding. 27  Now we have: Guest Lecture: Prof. Sasa Stefanovic Heterotrophic Plants 28