Lecture 12 - Hormone action and receptors | MCAT Biological and Biochemical Foundations PDF Download

 Page 1


Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
1 
 
                                                                            
 
Lesson Prepared Under MHRD project “National Mission 
on Education Through ICT” 
Discipline: Botany 
Paper: Plant Physiology 
National Coordinator: Prof. S.C. Bhatla 
Lesson: Hormone action and receptors 
Lesson Developer: Anita Thakur 
 Department/College: Department of Botany, University of Delhi
 
Lesson Reviewer: Prof. S.C. Bhatla 
Department of Botany, University of Delhi 
Language Editor: Vinee Khanna 
Department/College: Department of Genetics, University of Delhi, South 
Campus 
Lesson Editor: Dr. Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
 
 
Page 2


Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
1 
 
                                                                            
 
Lesson Prepared Under MHRD project “National Mission 
on Education Through ICT” 
Discipline: Botany 
Paper: Plant Physiology 
National Coordinator: Prof. S.C. Bhatla 
Lesson: Hormone action and receptors 
Lesson Developer: Anita Thakur 
 Department/College: Department of Botany, University of Delhi
 
Lesson Reviewer: Prof. S.C. Bhatla 
Department of Botany, University of Delhi 
Language Editor: Vinee Khanna 
Department/College: Department of Genetics, University of Delhi, South 
Campus 
Lesson Editor: Dr. Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
 
 
Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
2 
 
Table of contents 
Hormone action and receptors 
? Introduction 
? Auxins 
? Auxin signalling 
? Gibberellins 
? GA receptors and signalling 
? Ethylene 
? Ethylene receptors 
? Cytokinins 
? Cytokinin receptors  
? Abscisic acid 
? ABA receptors 
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
Page 3


Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
1 
 
                                                                            
 
Lesson Prepared Under MHRD project “National Mission 
on Education Through ICT” 
Discipline: Botany 
Paper: Plant Physiology 
National Coordinator: Prof. S.C. Bhatla 
Lesson: Hormone action and receptors 
Lesson Developer: Anita Thakur 
 Department/College: Department of Botany, University of Delhi
 
Lesson Reviewer: Prof. S.C. Bhatla 
Department of Botany, University of Delhi 
Language Editor: Vinee Khanna 
Department/College: Department of Genetics, University of Delhi, South 
Campus 
Lesson Editor: Dr. Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
 
 
Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
2 
 
Table of contents 
Hormone action and receptors 
? Introduction 
? Auxins 
? Auxin signalling 
? Gibberellins 
? GA receptors and signalling 
? Ethylene 
? Ethylene receptors 
? Cytokinins 
? Cytokinin receptors  
? Abscisic acid 
? ABA receptors 
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
3 
 
Learning outcomes: 
The student will be able to 
? Know about basics of hormones 
? Understand the importance of signal transduction pathways 
? Know about various kinds of phytohormones  
? Understand structures and pathway of auxin biosynthesis 
? Understand the role of auxin signalling 
? Know about gibberellins and its receptors 
? Know about triple response caused by ethylene 
? Understand the pathway of ethylene biosynthesis 
? Know about the types of cytokinins and their roles 
? Learn about the role of cytokinin receptors in signalling  
? Explain the pathway of abscisic acid biosynthesis 
? Know about the properties and applications of abscisic acid 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 4


Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
1 
 
                                                                            
 
Lesson Prepared Under MHRD project “National Mission 
on Education Through ICT” 
Discipline: Botany 
Paper: Plant Physiology 
National Coordinator: Prof. S.C. Bhatla 
Lesson: Hormone action and receptors 
Lesson Developer: Anita Thakur 
 Department/College: Department of Botany, University of Delhi
 
Lesson Reviewer: Prof. S.C. Bhatla 
Department of Botany, University of Delhi 
Language Editor: Vinee Khanna 
Department/College: Department of Genetics, University of Delhi, South 
Campus 
Lesson Editor: Dr. Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
 
 
Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
2 
 
Table of contents 
Hormone action and receptors 
? Introduction 
? Auxins 
? Auxin signalling 
? Gibberellins 
? GA receptors and signalling 
? Ethylene 
? Ethylene receptors 
? Cytokinins 
? Cytokinin receptors  
? Abscisic acid 
? ABA receptors 
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
3 
 
Learning outcomes: 
The student will be able to 
? Know about basics of hormones 
? Understand the importance of signal transduction pathways 
? Know about various kinds of phytohormones  
? Understand structures and pathway of auxin biosynthesis 
? Understand the role of auxin signalling 
? Know about gibberellins and its receptors 
? Know about triple response caused by ethylene 
? Understand the pathway of ethylene biosynthesis 
? Know about the types of cytokinins and their roles 
? Learn about the role of cytokinin receptors in signalling  
? Explain the pathway of abscisic acid biosynthesis 
? Know about the properties and applications of abscisic acid 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
4 
 
Introduction 
Hormones act as chemical messengers by way of their production in one part of the 
plant, get transported to target areas where they elicit responses. Endocrine hormones 
are the ones which are transported away from their site of synthesis to their sites of 
action in tissues whereas those hormones whose sites of synthesis and action are 
adjacent to each other are paracrine hormones.  
 Plant hormones are signal molecules that are produced within the plant in extremely low 
concentrations that regulate the growth processes. The ability of a hormone to induce a 
specific response in a target cell is usually mediated by specific proteins, known as 
hormone receptor. These are linked to signal transduction pathways. 
 
Did you know? Signal transduction is a process where cells construct responses 
to a signal either exterior or interior that triggers a cascade of events.  
 
 
 
 
 
 
 
 
 
 
 
 
Figure: When and why does Signal transduction occur? 
Source: http://www.authorstream.com/Presentation/Agriadda-2054799-indole-acetic-
acid-auxin-signal-transduction/  
Page 5


Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
1 
 
                                                                            
 
Lesson Prepared Under MHRD project “National Mission 
on Education Through ICT” 
Discipline: Botany 
Paper: Plant Physiology 
National Coordinator: Prof. S.C. Bhatla 
Lesson: Hormone action and receptors 
Lesson Developer: Anita Thakur 
 Department/College: Department of Botany, University of Delhi
 
Lesson Reviewer: Prof. S.C. Bhatla 
Department of Botany, University of Delhi 
Language Editor: Vinee Khanna 
Department/College: Department of Genetics, University of Delhi, South 
Campus 
Lesson Editor: Dr. Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
 
 
Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
2 
 
Table of contents 
Hormone action and receptors 
? Introduction 
? Auxins 
? Auxin signalling 
? Gibberellins 
? GA receptors and signalling 
? Ethylene 
? Ethylene receptors 
? Cytokinins 
? Cytokinin receptors  
? Abscisic acid 
? ABA receptors 
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
3 
 
Learning outcomes: 
The student will be able to 
? Know about basics of hormones 
? Understand the importance of signal transduction pathways 
? Know about various kinds of phytohormones  
? Understand structures and pathway of auxin biosynthesis 
? Understand the role of auxin signalling 
? Know about gibberellins and its receptors 
? Know about triple response caused by ethylene 
? Understand the pathway of ethylene biosynthesis 
? Know about the types of cytokinins and their roles 
? Learn about the role of cytokinin receptors in signalling  
? Explain the pathway of abscisic acid biosynthesis 
? Know about the properties and applications of abscisic acid 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
4 
 
Introduction 
Hormones act as chemical messengers by way of their production in one part of the 
plant, get transported to target areas where they elicit responses. Endocrine hormones 
are the ones which are transported away from their site of synthesis to their sites of 
action in tissues whereas those hormones whose sites of synthesis and action are 
adjacent to each other are paracrine hormones.  
 Plant hormones are signal molecules that are produced within the plant in extremely low 
concentrations that regulate the growth processes. The ability of a hormone to induce a 
specific response in a target cell is usually mediated by specific proteins, known as 
hormone receptor. These are linked to signal transduction pathways. 
 
Did you know? Signal transduction is a process where cells construct responses 
to a signal either exterior or interior that triggers a cascade of events.  
 
 
 
 
 
 
 
 
 
 
 
 
Figure: When and why does Signal transduction occur? 
Source: http://www.authorstream.com/Presentation/Agriadda-2054799-indole-acetic-
acid-auxin-signal-transduction/  
Hormone action and receptors 
 
Institute of Lifelong Learning, University of Delhi                                                                                  
5 
 
Efficient communication within the plants, among its various organs, tissues and cells, 
helps in the proper functioning of the systems. Increase or decrease in the levels of 
hormones depends on the signals perceived. The hormones then report to the sites of 
action or the target sites where they interact with the receptors. This interaction can 
induce a physiological or developmental response due to the involvement of some 
transcriptional or post-transcriptional events, such as phosphorylation, protein turnover, 
ion extrusion etc.  
 
Figure: Possible pathways of transmission of signal by the interaction of a hormone with 
the receptor molecules. (Permission to be sought)  
Source: http://en.wikipedia.org/wiki/Nuclear_receptor (CC) 
Some major classes of hormones include: auxins, cytokinins, gibberellins, ethylene 
and abscisic acid.