Lecture 14 - Plant defense against pathogens I | Plant Metabolism - Botany PDF Download

 Page 1


Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     1 
                                                                            
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant Physiology 
Lesson: Plant Defense against Pathogens-I 
Lesson Developer: Anita Thakur 
 Department/College: Department of Botany, 
University of Delhi
 
 
   
Page 2


Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     1 
                                                                            
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant Physiology 
Lesson: Plant Defense against Pathogens-I 
Lesson Developer: Anita Thakur 
 Department/College: Department of Botany, 
University of Delhi
 
 
   
Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     2 
Table of contents 
Plant Defense against Pathogens-I 
• Introduction 
• What study plant pathogen interaction 
• Plant disease 
• Types of plant-microbe relationships 
• Constitutive and inducible defenses 
• Plant pathogens and their strategies of pathogenesis 
• Plant pathogens 
• Types of plant pathogens and their modes of entry in host 
plants 
• Plant defense systems 
• Structural defenses 
• Chemical defenses 
• Enzymes and Proteins 
• Summary 
• Exercise/Practice 
• Glossary 
• References/bibliography/ further reading  
 
Page 3


Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     1 
                                                                            
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant Physiology 
Lesson: Plant Defense against Pathogens-I 
Lesson Developer: Anita Thakur 
 Department/College: Department of Botany, 
University of Delhi
 
 
   
Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     2 
Table of contents 
Plant Defense against Pathogens-I 
• Introduction 
• What study plant pathogen interaction 
• Plant disease 
• Types of plant-microbe relationships 
• Constitutive and inducible defenses 
• Plant pathogens and their strategies of pathogenesis 
• Plant pathogens 
• Types of plant pathogens and their modes of entry in host 
plants 
• Plant defense systems 
• Structural defenses 
• Chemical defenses 
• Enzymes and Proteins 
• Summary 
• Exercise/Practice 
• Glossary 
• References/bibliography/ further reading  
 
Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     3 
Learning outcomes 
The student will be able to 
• Understand the basic concepts of plant-pathogen interaction 
• Learn the types of host-pathogen interactions 
• Understand the concepts of disease, injury, and the signs and symptoms of plant 
pathogenic agents 
• Explain the various defense mechanisms adopted by plants 
• Describe terms like pathogenicity, non-host, non-pathogen, host range. 
• Differentiate between constitutive and induced defenses 
• Explain the various structural barriers present in plants which help in plant defense 
against pathogens 
• Become familiar with chemical compounds secreted by plants which play role in 
defense 
 
 
 
 
 
 
 
 
 
 
Page 4


Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     1 
                                                                            
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant Physiology 
Lesson: Plant Defense against Pathogens-I 
Lesson Developer: Anita Thakur 
 Department/College: Department of Botany, 
University of Delhi
 
 
   
Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     2 
Table of contents 
Plant Defense against Pathogens-I 
• Introduction 
• What study plant pathogen interaction 
• Plant disease 
• Types of plant-microbe relationships 
• Constitutive and inducible defenses 
• Plant pathogens and their strategies of pathogenesis 
• Plant pathogens 
• Types of plant pathogens and their modes of entry in host 
plants 
• Plant defense systems 
• Structural defenses 
• Chemical defenses 
• Enzymes and Proteins 
• Summary 
• Exercise/Practice 
• Glossary 
• References/bibliography/ further reading  
 
Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     3 
Learning outcomes 
The student will be able to 
• Understand the basic concepts of plant-pathogen interaction 
• Learn the types of host-pathogen interactions 
• Understand the concepts of disease, injury, and the signs and symptoms of plant 
pathogenic agents 
• Explain the various defense mechanisms adopted by plants 
• Describe terms like pathogenicity, non-host, non-pathogen, host range. 
• Differentiate between constitutive and induced defenses 
• Explain the various structural barriers present in plants which help in plant defense 
against pathogens 
• Become familiar with chemical compounds secreted by plants which play role in 
defense 
 
 
 
 
 
 
 
 
 
 
Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     4 
Introduction 
Why study plant-pathogen interaction? 
Plants are continuously confronted with a wide range of potential pathogens in their 
environment. Under favorable conditions, plant pathogenic microorganisms such as fungi, 
bacteria and viruses, can multiply and spread rapidly through plant populations to cause 
severe outbreaks of disease. Although plants are immobile and lack an immune system in 
comparison to animals, each plant cell possesses both a preformed (constitutive) and an 
inducible defense capacity. Since plants are the primary producers in an ecosystem and are 
a rich source of nutrients and energy for other organisms, including humans, the health of 
plants is of vital importance. Disease is one of the major factors that affect plant growth and 
productivity by limiting the quality, quantity and availability of staple foods. Major diseases 
of crop plants caused by plant pathogens are a considerable threat to global food security. 
The coevolution of plant pathogens and their hosts has resulted in highly adapted microbial 
invasion strategies and counter-defense mechanisms in plants. Plants have developed an 
array of structural, and chemical defenses to protect themselves from extensive damage 
caused by pathogens. Understanding how plants defend themselves against disease-causing 
organisms is of fundamental importance, in order to develop highly disease-resistant plant 
species and protect our food supply. A detailed study of the mechanisms by which plant and 
pathogenic organisms interact provides sustainable practice methods and solutions for the 
control of plant disease in agricultural crops. Uncontrolled plant diseases may result in lower 
crop yield and higher food prices or in poor quality of food, which is unfit for consumption. 
Some plant diseases may eliminate entire plant species while others affect the beauty and 
landscape of our environment. Plant-pathogen interaction studies help in elucidating the 
signaling mechanisms by which plant cells cope with a stress situation. Also investigations 
on plant-pathogen interactions help us in determining how organisms from different 
kingdoms communicate with each other. 
Plant pathology is the study of all aspects of plant diseases, including causal agents, their 
diagnosis, mechanisms by which disease is induced, physiological effects, methods of 
preventing or controlling the disease and reducing the damage caused. 
 
 
 
Page 5


Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     1 
                                                                            
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant Physiology 
Lesson: Plant Defense against Pathogens-I 
Lesson Developer: Anita Thakur 
 Department/College: Department of Botany, 
University of Delhi
 
 
   
Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     2 
Table of contents 
Plant Defense against Pathogens-I 
• Introduction 
• What study plant pathogen interaction 
• Plant disease 
• Types of plant-microbe relationships 
• Constitutive and inducible defenses 
• Plant pathogens and their strategies of pathogenesis 
• Plant pathogens 
• Types of plant pathogens and their modes of entry in host 
plants 
• Plant defense systems 
• Structural defenses 
• Chemical defenses 
• Enzymes and Proteins 
• Summary 
• Exercise/Practice 
• Glossary 
• References/bibliography/ further reading  
 
Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     3 
Learning outcomes 
The student will be able to 
• Understand the basic concepts of plant-pathogen interaction 
• Learn the types of host-pathogen interactions 
• Understand the concepts of disease, injury, and the signs and symptoms of plant 
pathogenic agents 
• Explain the various defense mechanisms adopted by plants 
• Describe terms like pathogenicity, non-host, non-pathogen, host range. 
• Differentiate between constitutive and induced defenses 
• Explain the various structural barriers present in plants which help in plant defense 
against pathogens 
• Become familiar with chemical compounds secreted by plants which play role in 
defense 
 
 
 
 
 
 
 
 
 
 
Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     4 
Introduction 
Why study plant-pathogen interaction? 
Plants are continuously confronted with a wide range of potential pathogens in their 
environment. Under favorable conditions, plant pathogenic microorganisms such as fungi, 
bacteria and viruses, can multiply and spread rapidly through plant populations to cause 
severe outbreaks of disease. Although plants are immobile and lack an immune system in 
comparison to animals, each plant cell possesses both a preformed (constitutive) and an 
inducible defense capacity. Since plants are the primary producers in an ecosystem and are 
a rich source of nutrients and energy for other organisms, including humans, the health of 
plants is of vital importance. Disease is one of the major factors that affect plant growth and 
productivity by limiting the quality, quantity and availability of staple foods. Major diseases 
of crop plants caused by plant pathogens are a considerable threat to global food security. 
The coevolution of plant pathogens and their hosts has resulted in highly adapted microbial 
invasion strategies and counter-defense mechanisms in plants. Plants have developed an 
array of structural, and chemical defenses to protect themselves from extensive damage 
caused by pathogens. Understanding how plants defend themselves against disease-causing 
organisms is of fundamental importance, in order to develop highly disease-resistant plant 
species and protect our food supply. A detailed study of the mechanisms by which plant and 
pathogenic organisms interact provides sustainable practice methods and solutions for the 
control of plant disease in agricultural crops. Uncontrolled plant diseases may result in lower 
crop yield and higher food prices or in poor quality of food, which is unfit for consumption. 
Some plant diseases may eliminate entire plant species while others affect the beauty and 
landscape of our environment. Plant-pathogen interaction studies help in elucidating the 
signaling mechanisms by which plant cells cope with a stress situation. Also investigations 
on plant-pathogen interactions help us in determining how organisms from different 
kingdoms communicate with each other. 
Plant pathology is the study of all aspects of plant diseases, including causal agents, their 
diagnosis, mechanisms by which disease is induced, physiological effects, methods of 
preventing or controlling the disease and reducing the damage caused. 
 
 
 
Plant defense against pathogens I 
Institute of Lifelong Learning, University of Delhi                                                     5 
Plant disease 
Plants are considered healthy when they can carry out their physiological functions to the 
best of their genetic potential. Disease, in a broad sense, is any physiological abnormality or 
significant dysfunction of normal physiological processes in plants, caused by a 
microorganism or an abiotic factor. When a plant, or any of its plant parts, is not able to 
carry out the essential functions because of interactions with pathogenic microbes, 
parasites, or adverse environmental factors, then the plant is said to be diseased.  
 
Figure: Possible disease symptoms in a plant 
Source: ILLL 
In a diseased plant, the activities of the cells are disrupted, altered, or inhibited, and the 
cells malfunction or die. At first the affliction is invisible and localized to one or a few cells. 
Soon, the reaction spreads and the alterations in the affected plant parts become visible. 
These visible changes are referred to as symptoms of the disease. Symptoms are the 
internal or external adverse changes in a plant or plant part, produced as a result of 
infection caused by an organism or any unfavorable environmental condition. Signs are 
physical indications of the presence of a disease-causing agent. The visible and measurable 
effects or alterations exhibited by a plant suffering from disease are a measure of the extent 
of disease in the plant. Disease in plants, thus, can be defined as a series of adverse