Title: Lecture 31 Plant Defense and Secondary Metabolites Alkaloids and Flavonoids
1Lecture 31 Plant Defense andSecondary
Metabolites Alkaloids and Flavonoids
2Three Groups of Secondary Metabolites
Limonoids Saponins Pinene
Flavonoids Anthocyanins Salicylic acid Lignin
Alkaloids Nicotine Morphine Cocaine Caffeine Gluco
sinolates
3Alkaloids
- 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
4Uses of Alkaloids
Pharmaceuticals Stimulants,
Narcotics Nicotine Cocaine Caffeine Morphine
Coffee
Cocoa
Tobacco
Opium Poppy
5Uses of Alkaloids
6Some Examples of Alkaloids and Their Structures
7Nicotine
Anti-herbivory Causes addiction Decreases
appetite Induced upon wounding/insect
attack Expensive for plant to make
8Nicotine and Herbivory
Induced defense upon herbivory - Nicotine
synthesis in roots - Transport to shoot - JA
mediates signal transduction
9Some herbivores can become adapted to tolerate
plant defense substancesAn example
Pyrrolizidine
Cinnabar moth
Non-toxic form, stored in plants
Toxic form, passes through membranes
10Phenols
11Role 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)
12Phenolics are synthesized in different ways
Roundup
13Biosynthesis 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
14Biosynthesis of Phenols from Phenylalanine
15Some Phenolic Compounds
- Activated by light ? phototoxic - level may
increase 100fold in stressed plants -
causing skin rashes on humans
16Flavonoids
17Anthocyanins are Colored Flavonoids that Attract
Animals
18Effects of Ring Substitutes on Anthocyanidin Color
19Flavones 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