Introduction to Plant Secondary Metabolism

1. New developments in study of plant secondary metabolites

a) chemistry

b) instruments for characterization and for separation/purification

c) biological techniques

d) tissue/cell culture

e) isolation of organelles

f) bioassays

g) molecular studies

2. What are secondary metabolites?

they arise (arose) from primary pathways

found both in prokaryotes and eukaryotes

diploid, polyploid

waste products

excretion
turnover
catabolism
detoxification

functions of secondary compounds - internal

"overflow" hypothesis

"increase in fitness"

retention of inactive compounds?

"cost"? carbon versus nitrogen

3. Variation in secondary metabolites

plant parts/time-phenology-development

"polymorphism"

stress

hybridization

transport?

mechanisms of accumulation and storage almost unstudied

4. Interactive roles of secondary metabolites

with animals-insects-other plants-fungi-bacteria - both positive and negative interactions

simultaneous evolution

variation in both plant populations and the populations of organisms that are interacting

generalists versus specialists

allomones-kairomones-synomones

"chemical ecology"

Why do we have so many secondary compounds?

The basic biochemical systems are similar in many cases.

5. Evolution of "complex" compounds

simple compounds widespread

complex compounds usually have limited distribution

value for studying plant evolutionary relationships

loss of ability to synthesize a particular group of compounds occurs in some lines

sometimes replacement with a "functionally" similar group of compounds

"gene transfer"?

Reactions common to all groups of plants -- starting points

1. catabolic processes- breakdown for energy in many cases

a) glycolysis glucose to pyruvate

b) pentose phosphate CO₂ and NADPH

c) TCA cycle acetyl-CoA to CO₂ and ATP

source of intermediates

d) glyoxylate cycle - parallels the TCA cycle

2. synthetic cycles

a) photosynthesis CO₂ to NADPH, ATP, and glucose

b) reductive pentose (Calvin) cycle

c) others oxidative photosynthetic pathways etc.

d) gluconeogenesis

3. Energy storage

sucrose

starch

protein

lipids

others

4. structural

cellulose

lignin

pectins

Energy rich cofactors

ATP

NADPH

NADH

FADH

Formation and hydrolysis of glycosides - solubility, reduced activity

UDP-glucose, others

β-glycosidases

Oxygenases

monooxygenases - cytochrome P-450 dependent

dioxygenases

methylation/demethylation

SAM major source

methyl transferases

Related Images

Outline of Secondary Metabolism

© David S. Seigler, Integrative Biology 425, Plant Secondary Metabolism, Department of Plant Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana, Illinois 61801, USA. 217-333-7577. seigler@life.uiuc.edu.