PLANT PHYSIOLOGY

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PLANT PHYSIOLOGY

Az Agrármérnöki MSc szak tananyagfejlesztése TÁMOP-4.1.2-08/1/A-2009-0010

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Secondary metabolites in

plant defense

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Overview

1. Secondary metabolites

2. Induced plant defenses against insect herbivores

3. Plant defenses against pathogens

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1. Secondary metabolites

1.1. Terpenes

1.2. Phenolic compounds

1.3. Nitrogen-containing compounds

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A simplified view of the major pathways of secondary-metabolite biosynthesis and their interrelationships with primary metabolism

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Outline of terpene biosynthesis

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Structures of limonene (A) and menthol (B): these two well-known monoterpenes serve as defenses against insects and other organisms

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Monoterpenes and sesquiterpenes are commonly found inglandular hairs on the plant surface

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Structure of two triterpenes, azadirachtin (A), and α-ecdysone (B), which serve as powerful insecticides

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Plant phenolics are biosynthesized in several different ways

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Outline of phenolic biosynthesis from phenylalanine onward

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Simple phenolic compounds play a great diversity of roles in plants

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Structure of some tannins formed from phenolic acids or flavonoid units

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Proposed mechanisms for the interaction of tannins with proteins

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Examples of alkaloids, a diverse group of secondary metabolites that contain nitrogen

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Nicotine biosynthesis begins with the biosynthesis of the nicotinic acid

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Two forms of pyrrolizidine alkaloids occur in nature: the N-oxide form and the tertiary alkaloid

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Enzyme-catalyzed hydrolysis of cyanogenic glycosides to release hydrogen cyanide

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Hydrolysis of glucosinolates to mustard-smelling volatiles

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2. Induced plant defenses against insect herbivores

2.1. Plants can recognize specific components of insect saliva

2.1. Jasmonic acid activates many defensive responses 2.3. Some plant proteins inhibit herbivore digestion

2.4. Herbivore-induced volatiles have complex ecological functions

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Steps in the pathway for conversion of linolenic acid (18:3) to jasmonic acid

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A model for jasmonic acid signaling

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3. Plant defenses against pathogens

3.1. Some antimicrobial compounds are synthesized before pathogen attack

3.2. Infection induces additional antipathogen defenses 3.3. Phytoalexins often increase after pathogen attack 3.4. Some plants recognize specific pathogen-derived substances

3.5. A single encounter with a pathogen may increase resistance to future attacks

3.6. Interactions of plants with non-pathogenic bacteria can trigger induced systemic resistance

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Many types of antipathogen defenses are induced by infection

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Structure of some phytoalexins found in two different plant families

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Initial pathogen infection may increase resistance to future pathogen attack through development of systemic acquired resistance (SAR)

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Exposure to nonpathogenic microorganisms may increase resistance to future pathogen attack through development of induced systemic

resistance (ISR)

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Summary

Because they are sessile organisms, plants often use secondary metabolites in much the same way animals use behavior to interact with their environment. Among their many functions, secondary metabolites serve to

attract beneficial organisms such as pollinators and seed- dispersing animals, to protect against herbivores and

pathogens. There are three major groups of secondary

metabolites: terpenes, phenolics, and nitrogen-containing compounds. The study of plant secondary metabolites

has many practical applications. The breeding of increased levels of secondary metabolites into crop

plants has made it possible to reduce the need for certain

costly and potentially harmful pesticides.

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PLANT PHYSIOLOGY

Secondary metabolites in

plant defense

Overview

1. Secondary metabolites

2. Induced plant defenses against insect herbivores

3. Plant defenses against pathogens

1. Secondary metabolites

2. Induced plant defenses against insect herbivores

3. Plant defenses against pathogens

Summary

Because they are sessile organisms, plants often use secondary metabolites in much the same way animals use behavior to interact with their environment. Among their many functions, secondary metabolites serve to

attract beneficial organisms such as pollinators and seed- dispersing animals, to protect against herbivores and

pathogens. There are three major groups of secondary

metabolites: terpenes, phenolics, and nitrogen-containing compounds. The study of plant secondary metabolites

has many practical applications. The breeding of increased levels of secondary metabolites into crop

plants has made it possible to reduce the need for certain

costly and potentially harmful pesticides.

Questions

• Discuss the main functions of secondary metabolites in plants and relate these functions to the sites of

accumulation of secondary compounds in the plant.

• What are terpenes chemically, and how are they synthesized?

• How do alkaloids differ structurally from the other

secondary compounds? Given their biological effects, how might they function ecologically?

• Do plants, like animals, have an immune response to

pathogens?

THANK YOU FOR YOUR ATTENTION

Next lecture:

Overview of plant growth and development

• Compiled by:

Prof. Vince Ördög