Lecture 31 Plant Defense and Secondary Metabolites Alkaloids and Flavonoids - PowerPoint PPT Presentation

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Lecture 31 Plant Defense and Secondary Metabolites Alkaloids and Flavonoids

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20% of plant species contain alkaloids. Mainly involved in plant defense against herbivores and ... Most are alkaline. Increase in response to herbivore attack ... – PowerPoint PPT presentation

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Title: Lecture 31 Plant Defense and Secondary Metabolites Alkaloids and Flavonoids


1
Lecture 31 Plant Defense andSecondary
Metabolites Alkaloids and Flavonoids
2
Three Groups of Secondary Metabolites
Limonoids Saponins Pinene
Flavonoids Anthocyanins Salicylic acid Lignin
Alkaloids Nicotine Morphine Cocaine Caffeine Gluco
sinolates
3
Alkaloids
  • Low Molecular weight Nitrogenous compounds
  • 20 of plant species contain alkaloids
  • Mainly involved in plant defense against
    herbivores and pathogens
  • Led to rapid utilization by humans
  • Synthesized from lysine, tryptophan, tyrosine
  • Most are alkaline
  • Increase in response to herbivore attack
  • Alkaloid-containing plants lupines, larkspur,
    tobacco, coffee

4
Uses of Alkaloids
Pharmaceuticals Stimulants,
Narcotics Nicotine Cocaine Caffeine Morphine
Coffee
Cocoa
Tobacco
Opium Poppy
5
Uses of Alkaloids
6
Some Examples of Alkaloids and Their Structures
7
Nicotine
Anti-herbivory Causes addiction Decreases
appetite Induced upon wounding/insect
attack Expensive for plant to make
8
Nicotine and Herbivory
Induced defense upon herbivory - Nicotine
synthesis in roots - Transport to shoot - JA
mediates signal transduction
9
Some herbivores can become adapted to tolerate
plant defense substancesAn example
Pyrrolizidine
Cinnabar moth
Non-toxic form, stored in plants
Toxic form, passes through membranes
10
Phenols
11
Role of Phenolics in Plants
  • Nearly 10,000 individual compounds
  • Large chemical diversity
  • Defense compounds against herbivores and
    pathogens (Tannins, Isoflavanoids)
  • Mechanical support (Lignin)
  • Attract pollinators and fruit dispersers
    (Anthocyanins)
  • Absorb harmful UV radiation (Flavonoids)

12
Phenolics are synthesized in different ways
Roundup
13
Biosynthesis of Phenols from Phenylalanine
PAL - important regulatory step in formation of
many phenolic compounds PAL is increased by
environmental stress (nutrient deficiency, light,
fungal infection) transcriptional regulation
14
Biosynthesis of Phenols from Phenylalanine
15
Some Phenolic Compounds
- Activated by light ? phototoxic - level may
increase 100fold in stressed plants -
causing skin rashes on humans
16
Flavonoids
17
Anthocyanins are Colored Flavonoids that Attract
Animals
18
Effects of Ring Substitutes on Anthocyanidin Color
19
Flavones and Flavonols absorb UV light
Black-eyed Susan (Rudbeckia sp.) as
seen by humans and by honeybees
UV-absorbing flavonols are found in inner parts
of the rays but not in the tip
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