Defense: (including spikes and chemicals)

Questions Any questions?

Tho' Nature, red in tooth and claw

Ferns Angiosperms Gymnosperms

Herbivory Historically who is the most important? – Insects! Earliest forms would have been chewing leaves but diversification to sap sucking, leaf mining, gall forming, and nectar feeding.

Herbivory Historically who is the most important? – Insects! Earliest forms would have been chewing leaves but diversification to sap sucking, leaf mining, gall forming, and nectar feeding.

Herbivory Our oldest fossils have evidence of herbivory

Defense Types – Constitutive: Always present External/mechanical and large quantitative – Induced: Produced after exposure to an herbivore Can be localized or systemic Secondary compounds, morphology and physiology Advantage?

Chemical defense 25,000 secondary metabolites found in plants – Why secondary? They are not used for photosynthetic and metabolic pathways and are often byproducts.

Chemical defense Herbivores – Qualitative: toxins in low concentrations (up to 10% of fresh weight) Not dosage dependent, causes problems with herbivore metabolic pathways Small, water soluble, quick to produce and cheap to transport and store Alkaloids, cyanogenic glycosides, non-protein amino acids, cardiac glycosides, glucosinolates, proteins Non-adapted specialists and generalists

Chemical defense Herbivores – Quantitative: high concentrations Dosage dependent Reduce digestibility and/or palatability – Block digestive enzymes, bind proteins being digested or disrupt protein activity in gut wall – Tannins and lignin increase toughness Large, expensive and slow to produce and transport Phenolic compounds (phenolic acids, lignins, tannins) Specialists and generalists

Chemical defense Chemically, three main types – Nitrogen-based: alkaloids, cyanogenic glycosides and glucosinolates Alkaloids (>3000): from amino acids, includes lots of good stuff (nicotine, caffeine, morphine, strychnine, quinine, ergoline). Many effects, inhibit enzymes, alter carbohydrate and fat storage, bind nucleic acids, affect cell membrane, cytoskeleton, nerves Cyanogenic glycosides: stored inactive in vacuoles and released when cell membranes are broken, enzymes transform to hydrogen cyanide, block respiration Glucosinolates: similar activation to CG

Chemical defense Chemically, three main types – Terpenoids or isoprenoids (>10,000): 5-C isporene units Monoterpenoids: 2 isporene units, volatile essential oils & iridoids Diterpenoids: 4 isoprene units, latex and resins (Rhododendron leaves!) Plant steroids and sterols: vitamin D, glycosides (e.g., digitalis), saponins (lyse red blood cells)

Chemical defense Chemically, three main types – Phenolics or phenols: Aromatic 6 C with a hydroxyl group (e.g., lignin, silymarin, cannabinoids) Tannins: hydrolizable (ellagic acid) and non hydrolizable (proanthocyanidins) Flavonoids (pigmentation): – Condensed tannins: 2-50 flavonoid groups bind plant proteins during digestion Polyphenols: antioxidants

Chemical defense Indigestible chemicals: – Lignin, silica, stone cells (sclereids): grind down chewing parts

Other chemicals Also used for defense: – Fatty acids, amino acids, peptides – Heavy metals: iron (grasses) and aluminum

Chemical defense Pathogens – Constitutive Accumulation of compounds (e.g., silicon, heavy metals) Production of antimicrobial compounds (alkaloids, flavonoids, lignin, saponins) Production of lipid transfer proteins effecting light and temperature Lectins (can hydrolize fungal cell walls) and thionins (cysteine-rich proteins) – Also inducible: Basal, Hypersensitive (Systemic Acquired Resistance), RNA Silencing

Chemical defense Why chemical distributions are tricky – Presence/absence versus concentration – Spatial and temporal distribution in plant – A given compound can break down into many others – The same chemical can be produced by different pathways Furanocoumarins in Ficus, Apiaceae and Rutaceae – And, The same pathway can produce different chemicals

Chemical defenses Phylogenetic associations – Glucosinolates (Brassicales), Gums (scattered but in Fabaceae), Iridoids – C-10 (asterids and Saxifragales) may be useful – Ellagic acid (hydrolizable tannin) is restricted in distribution

Chemical defenses Phylogenetic associations – Alkaloids and flavonoids (e.g., anthocyanins) and saponins are in lots of groups. Terepenoids found in all taxa (15,000 different types). – Dissimilar taxa being fed on by the same or similar herbivores may be similar chemical Catepillars: Magoliids and Rutaceae (alkaloids), Putranjivaceae and Brassicales (glucosinolates), and Daphniphyllaceae and asterids (iridoids)

Mechanical defense Many different external deterrents – Chemicals can be released externally: resin, lignin, silica, wax, gums – Sharp bits Spines: Vascularized, modified leaf or stipule Prickles: Several cells thick, not vascularized Thorns: Modified stem, usually dead Trichomes: Epidermal outgrowth, e.g., hair Can contain irritants (e.g., urticating hairs) and poisons – Thick protective layers

Defenses Other – Thigmonasty: respond to touch – Mimicry and crypsis: Pseudopanax in NZ, Spots that resemble insect eggs – Leaf shedding and colour change

Defenses Other – Indirect: mutualistic attraction of natural enemies Release of volatiles, Provision of shelters/food – And, many secondary compounds may actually be made by endophytes and bacteria! Convolvulaceae, Celastraceae, Fabaceae, Poaceae Terpenoids and some alkaloids made in chloroplasts and mitochondria – Some plant chemicals may be due to lateral gene transfer – And plant parasites may take up alkaloids

Evolution of anti-herbivore defenses

Ferns Angiosperms Gymnosperms

Question Has the diversity and complexity of secondary compounds in plants intensified over time?

Question Has the diversity and complexity of secondary compounds in plants intensified over time? – For 70 Bursera, measured volatile chemistry (volatile terpenes, alkanes and aromatic compounds) and built a molecular phylogeny

Resin canals with terpenesMain herbivore is the chrysomelid beetle Blephardia Coevolution for past 100 my

Question Has the diversity and complexity of secondary compounds in plants intensified over time? – For 70 Bursera, measured volatile chemistry and built a molecular phylogeny – # Compounds/species and compound diversity has increased over time. However, species diversification has been faster than chemical diversification.