Lecture 10 - Secretory Systems in Plants | Plant Anatomy - Biotechnology Engineering (BT) PDF Download

 Page 1


Secretory Systems in Plants 
1 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
Discipline: Botany 
Subject: Plant Anatomy 
Lesson: Secretory Systems in Plants 
Lesson Developer: Dharmendra Kumar Mallick 
College/Department: Deshbandhu College, University of Delhi 
Lesson Reviewer: Prof. S.C. Bhatla, Department of Botany, University 
of Delhi 
 
 
 
 
 
 
 
 
 
 
 
Page 2


Secretory Systems in Plants 
1 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
Discipline: Botany 
Subject: Plant Anatomy 
Lesson: Secretory Systems in Plants 
Lesson Developer: Dharmendra Kumar Mallick 
College/Department: Deshbandhu College, University of Delhi 
Lesson Reviewer: Prof. S.C. Bhatla, Department of Botany, University 
of Delhi 
 
 
 
 
 
 
 
 
 
 
 
Secretory Systems in Plants 
2 
Institute of Lifelong Learning, University of Delhi 
 
 
Table of Contents 
Chapter: Secretory Systems in Plants 
? Introduction 
? Mechanism of Secretion 
? Holocrine Secretion 
? Merocrine Secretion 
? Granulocrine Secretion 
? Eccrine Secretion 
? Classification of secretory structures 
? External Secretory Structures 
? Glandular Trichomes 
? Hydathodes 
? Salt glands and Chalk glands 
? Glandular trichomes secreting lipophilic substances 
? Nectaries 
? Colleters 
? Osmophores 
? The glandular structures of carnivorous plants 
? Internal Secretory Structures 
? Internal secretory cells 
? Types of internal Secretory Cells 
? Crystals and Silica secreting cells 
? Lithocysts 
? Myrosin cells 
? Oil cells 
? Mucilage cells 
? Tannin idioblasts 
? Secretory cavities and ducts 
? Schizogenous cavities 
Page 3


Secretory Systems in Plants 
1 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
Discipline: Botany 
Subject: Plant Anatomy 
Lesson: Secretory Systems in Plants 
Lesson Developer: Dharmendra Kumar Mallick 
College/Department: Deshbandhu College, University of Delhi 
Lesson Reviewer: Prof. S.C. Bhatla, Department of Botany, University 
of Delhi 
 
 
 
 
 
 
 
 
 
 
 
Secretory Systems in Plants 
2 
Institute of Lifelong Learning, University of Delhi 
 
 
Table of Contents 
Chapter: Secretory Systems in Plants 
? Introduction 
? Mechanism of Secretion 
? Holocrine Secretion 
? Merocrine Secretion 
? Granulocrine Secretion 
? Eccrine Secretion 
? Classification of secretory structures 
? External Secretory Structures 
? Glandular Trichomes 
? Hydathodes 
? Salt glands and Chalk glands 
? Glandular trichomes secreting lipophilic substances 
? Nectaries 
? Colleters 
? Osmophores 
? The glandular structures of carnivorous plants 
? Internal Secretory Structures 
? Internal secretory cells 
? Types of internal Secretory Cells 
? Crystals and Silica secreting cells 
? Lithocysts 
? Myrosin cells 
? Oil cells 
? Mucilage cells 
? Tannin idioblasts 
? Secretory cavities and ducts 
? Schizogenous cavities 
Secretory Systems in Plants 
3 
Institute of Lifelong Learning, University of Delhi 
? Resin ducts 
? Lysigenous cavities 
? Kino veins 
? Schizolysigenous cavities and ducts 
? Laticifers 
? Economic importance of secretions 
? Glossary 
? References/ Further Reading 
? Exercise/ Practice 
  
Page 4


Secretory Systems in Plants 
1 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
Discipline: Botany 
Subject: Plant Anatomy 
Lesson: Secretory Systems in Plants 
Lesson Developer: Dharmendra Kumar Mallick 
College/Department: Deshbandhu College, University of Delhi 
Lesson Reviewer: Prof. S.C. Bhatla, Department of Botany, University 
of Delhi 
 
 
 
 
 
 
 
 
 
 
 
Secretory Systems in Plants 
2 
Institute of Lifelong Learning, University of Delhi 
 
 
Table of Contents 
Chapter: Secretory Systems in Plants 
? Introduction 
? Mechanism of Secretion 
? Holocrine Secretion 
? Merocrine Secretion 
? Granulocrine Secretion 
? Eccrine Secretion 
? Classification of secretory structures 
? External Secretory Structures 
? Glandular Trichomes 
? Hydathodes 
? Salt glands and Chalk glands 
? Glandular trichomes secreting lipophilic substances 
? Nectaries 
? Colleters 
? Osmophores 
? The glandular structures of carnivorous plants 
? Internal Secretory Structures 
? Internal secretory cells 
? Types of internal Secretory Cells 
? Crystals and Silica secreting cells 
? Lithocysts 
? Myrosin cells 
? Oil cells 
? Mucilage cells 
? Tannin idioblasts 
? Secretory cavities and ducts 
? Schizogenous cavities 
Secretory Systems in Plants 
3 
Institute of Lifelong Learning, University of Delhi 
? Resin ducts 
? Lysigenous cavities 
? Kino veins 
? Schizolysigenous cavities and ducts 
? Laticifers 
? Economic importance of secretions 
? Glossary 
? References/ Further Reading 
? Exercise/ Practice 
  
Secretory Systems in Plants 
4 
Institute of Lifelong Learning, University of Delhi 
Introduction 
Unlike animals, it is difficult to distinguish secretion from excretion in plants. Secretion is 
defined as the elimination of substances which may still take part in metabolism whereas 
the excretion is the elimination of the end product of metabolism. Animals get rid of harmful 
and useless substances through their excretory system. The secretory system of animals is 
also well defined anatomically and physiologically. In plants, neither the structures involved 
in the release of substances nor the released substances can be easily categorized as 
secretory or excretory due to difficulty in ascertaining whether a substance is useful, 
harmful or superfluous for the plants releasing it. Therefore, only one term secretion is 
generally used to describe the various processes by which individual cells or multicellular 
structures perform any of the functions mentioned below. 
? Remain alive and discharge their products outside the plant body or into special 
nonliving ducts or cavities within the plant body. 
? Undergo lysis and rupture, releasing their contents, often into a duct. 
? Store the product within the living cell or between protoplast and wall of the cell. 
 
 
Figure: Leaves of mangrove showing salt secretion on its surface. 
Source: http://www.mesa.edu.au/mangroves/mangroves02.asp  
Page 5


Secretory Systems in Plants 
1 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
Discipline: Botany 
Subject: Plant Anatomy 
Lesson: Secretory Systems in Plants 
Lesson Developer: Dharmendra Kumar Mallick 
College/Department: Deshbandhu College, University of Delhi 
Lesson Reviewer: Prof. S.C. Bhatla, Department of Botany, University 
of Delhi 
 
 
 
 
 
 
 
 
 
 
 
Secretory Systems in Plants 
2 
Institute of Lifelong Learning, University of Delhi 
 
 
Table of Contents 
Chapter: Secretory Systems in Plants 
? Introduction 
? Mechanism of Secretion 
? Holocrine Secretion 
? Merocrine Secretion 
? Granulocrine Secretion 
? Eccrine Secretion 
? Classification of secretory structures 
? External Secretory Structures 
? Glandular Trichomes 
? Hydathodes 
? Salt glands and Chalk glands 
? Glandular trichomes secreting lipophilic substances 
? Nectaries 
? Colleters 
? Osmophores 
? The glandular structures of carnivorous plants 
? Internal Secretory Structures 
? Internal secretory cells 
? Types of internal Secretory Cells 
? Crystals and Silica secreting cells 
? Lithocysts 
? Myrosin cells 
? Oil cells 
? Mucilage cells 
? Tannin idioblasts 
? Secretory cavities and ducts 
? Schizogenous cavities 
Secretory Systems in Plants 
3 
Institute of Lifelong Learning, University of Delhi 
? Resin ducts 
? Lysigenous cavities 
? Kino veins 
? Schizolysigenous cavities and ducts 
? Laticifers 
? Economic importance of secretions 
? Glossary 
? References/ Further Reading 
? Exercise/ Practice 
  
Secretory Systems in Plants 
4 
Institute of Lifelong Learning, University of Delhi 
Introduction 
Unlike animals, it is difficult to distinguish secretion from excretion in plants. Secretion is 
defined as the elimination of substances which may still take part in metabolism whereas 
the excretion is the elimination of the end product of metabolism. Animals get rid of harmful 
and useless substances through their excretory system. The secretory system of animals is 
also well defined anatomically and physiologically. In plants, neither the structures involved 
in the release of substances nor the released substances can be easily categorized as 
secretory or excretory due to difficulty in ascertaining whether a substance is useful, 
harmful or superfluous for the plants releasing it. Therefore, only one term secretion is 
generally used to describe the various processes by which individual cells or multicellular 
structures perform any of the functions mentioned below. 
? Remain alive and discharge their products outside the plant body or into special 
nonliving ducts or cavities within the plant body. 
? Undergo lysis and rupture, releasing their contents, often into a duct. 
? Store the product within the living cell or between protoplast and wall of the cell. 
 
 
Figure: Leaves of mangrove showing salt secretion on its surface. 
Source: http://www.mesa.edu.au/mangroves/mangroves02.asp  
Secretory Systems in Plants 
5 
Institute of Lifelong Learning, University of Delhi 
The cells involved in secretion show the presence of dense protoplasts with other cellular 
components, the frequency of which is variable on the basis of the substance secreted. A 
common characteristic of mucilage secreting cells is the presence of abundant Golgi bodies. 
The mucilage is secreted by Golgi bodies and it is ejected from the protoplast by exocytosis.  
 
 
Figure: Electron micrograph of a maize root cap slime-secreting cell showing two Golgi 
stacks in the centre. These are surrounded by large white sacs filled with mucilage produced 
by the Golgi apparatus. 
Source: http://bscb.org/learning-resources/softcell-e-learning/golgi-apparatus/  
The characteristic feature of cells secreting lipophilic substances is the presence of 
endoplasmic reticulum. The endoplasmic reticulum is spatially associated with plastids that 
contain osmiophilic substances. The endoplasmic reticulum and dictyosomes, which are the 
most important organelles for most types of secretion, are present in all plant cells. 
Therefore all plant cells are considered as secretory.  
Golgi apparatus
Mucilage containing sacs