Lecture 13 - Sulphur metabolism | Plant Metabolism - Botany PDF Download

 Page 1


Sulphur Metabolism 
 
1 
Institute of Lifelong Learning, University of Delhi 
                                                                                                                                                      
 
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant physiology 
Lesson: Sulphur Metabolism 
Lesson Developer: Dhara Arora
 
Department/College: Department of Botany,  
University of Delhi
 
 
 
 
 
 
 
Page 2


Sulphur Metabolism 
 
1 
Institute of Lifelong Learning, University of Delhi 
                                                                                                                                                      
 
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant physiology 
Lesson: Sulphur Metabolism 
Lesson Developer: Dhara Arora
 
Department/College: Department of Botany,  
University of Delhi
 
 
 
 
 
 
 
Sulphur Metabolism 
 
2 
Institute of Lifelong Learning, University of Delhi 
 
Table of contents 
Sulfur Metabolism 
? Introduction 
? Biogeochemical sulfur cycle 
? CLAW hypothesis 
? Uptake of sulfur 
? Assimilation of sulfur 
? Regulation of sulfur assimilation 
? Light 
? Developmental stage 
? Availability of sulfur 
? Sulfur and Nitrogen assimilation 
? Significance 
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
Page 3


Sulphur Metabolism 
 
1 
Institute of Lifelong Learning, University of Delhi 
                                                                                                                                                      
 
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant physiology 
Lesson: Sulphur Metabolism 
Lesson Developer: Dhara Arora
 
Department/College: Department of Botany,  
University of Delhi
 
 
 
 
 
 
 
Sulphur Metabolism 
 
2 
Institute of Lifelong Learning, University of Delhi 
 
Table of contents 
Sulfur Metabolism 
? Introduction 
? Biogeochemical sulfur cycle 
? CLAW hypothesis 
? Uptake of sulfur 
? Assimilation of sulfur 
? Regulation of sulfur assimilation 
? Light 
? Developmental stage 
? Availability of sulfur 
? Sulfur and Nitrogen assimilation 
? Significance 
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
Sulphur Metabolism 
 
3 
Institute of Lifelong Learning, University of Delhi 
 
Learning outcomes: 
The student will be able to 
? Learn about different forms of sulfur 
? Become familiar with role of plants in climate regulation via sulfur 
metabolism 
? Understand what is CLAW hypothesis 
? Explain biogeochemical cycle of sulfur  
? Understand the method of uptake and transport of sulfur  
? Understand the stepwise reactions involved in sulfur metabolism  
? Appreciate how sulfur metabolism is tightly regulated at crucial steps 
? Explain the entire pathway of sulfur assimilation 
? Learn the crucial roles played by glutathione and cysteine in plant cells 
? Explain the reason behind pungency of onion and garlic. 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 4


Sulphur Metabolism 
 
1 
Institute of Lifelong Learning, University of Delhi 
                                                                                                                                                      
 
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant physiology 
Lesson: Sulphur Metabolism 
Lesson Developer: Dhara Arora
 
Department/College: Department of Botany,  
University of Delhi
 
 
 
 
 
 
 
Sulphur Metabolism 
 
2 
Institute of Lifelong Learning, University of Delhi 
 
Table of contents 
Sulfur Metabolism 
? Introduction 
? Biogeochemical sulfur cycle 
? CLAW hypothesis 
? Uptake of sulfur 
? Assimilation of sulfur 
? Regulation of sulfur assimilation 
? Light 
? Developmental stage 
? Availability of sulfur 
? Sulfur and Nitrogen assimilation 
? Significance 
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
Sulphur Metabolism 
 
3 
Institute of Lifelong Learning, University of Delhi 
 
Learning outcomes: 
The student will be able to 
? Learn about different forms of sulfur 
? Become familiar with role of plants in climate regulation via sulfur 
metabolism 
? Understand what is CLAW hypothesis 
? Explain biogeochemical cycle of sulfur  
? Understand the method of uptake and transport of sulfur  
? Understand the stepwise reactions involved in sulfur metabolism  
? Appreciate how sulfur metabolism is tightly regulated at crucial steps 
? Explain the entire pathway of sulfur assimilation 
? Learn the crucial roles played by glutathione and cysteine in plant cells 
? Explain the reason behind pungency of onion and garlic. 
 
 
 
 
 
 
 
 
 
 
 
 
 
Sulphur Metabolism 
 
4 
Institute of Lifelong Learning, University of Delhi 
 
Introduction 
Elemental sulfur is found in areas of volcanic activity or at places where sulfate 
minerals have been reduced by anaerobic bacteria.  
 
Figure: Various types of inorganic and organic sulfur, with structure of a few major 
forms. 
Source: Author 
 
Sulfur is an important macronutrient for plant growth. It is primarily used to 
synthesize amino acids and proteins, and in coenzymes and vitamins, such as 
coenzyme A, S-adenosylmethionine, thiamine, biotin and methylmethionine. 
Apart from these compounds, other forms of organic sulfur include sulfolipids, 
phytoalexins, redox compounds and many flavor and fragrance imparting 
compounds, such as diallyls of onion and garlic and the glucosinolates of 
brassicas and other crucifers.  
 
Page 5


Sulphur Metabolism 
 
1 
Institute of Lifelong Learning, University of Delhi 
                                                                                                                                                      
 
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant physiology 
Lesson: Sulphur Metabolism 
Lesson Developer: Dhara Arora
 
Department/College: Department of Botany,  
University of Delhi
 
 
 
 
 
 
 
Sulphur Metabolism 
 
2 
Institute of Lifelong Learning, University of Delhi 
 
Table of contents 
Sulfur Metabolism 
? Introduction 
? Biogeochemical sulfur cycle 
? CLAW hypothesis 
? Uptake of sulfur 
? Assimilation of sulfur 
? Regulation of sulfur assimilation 
? Light 
? Developmental stage 
? Availability of sulfur 
? Sulfur and Nitrogen assimilation 
? Significance 
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
Sulphur Metabolism 
 
3 
Institute of Lifelong Learning, University of Delhi 
 
Learning outcomes: 
The student will be able to 
? Learn about different forms of sulfur 
? Become familiar with role of plants in climate regulation via sulfur 
metabolism 
? Understand what is CLAW hypothesis 
? Explain biogeochemical cycle of sulfur  
? Understand the method of uptake and transport of sulfur  
? Understand the stepwise reactions involved in sulfur metabolism  
? Appreciate how sulfur metabolism is tightly regulated at crucial steps 
? Explain the entire pathway of sulfur assimilation 
? Learn the crucial roles played by glutathione and cysteine in plant cells 
? Explain the reason behind pungency of onion and garlic. 
 
 
 
 
 
 
 
 
 
 
 
 
 
Sulphur Metabolism 
 
4 
Institute of Lifelong Learning, University of Delhi 
 
Introduction 
Elemental sulfur is found in areas of volcanic activity or at places where sulfate 
minerals have been reduced by anaerobic bacteria.  
 
Figure: Various types of inorganic and organic sulfur, with structure of a few major 
forms. 
Source: Author 
 
Sulfur is an important macronutrient for plant growth. It is primarily used to 
synthesize amino acids and proteins, and in coenzymes and vitamins, such as 
coenzyme A, S-adenosylmethionine, thiamine, biotin and methylmethionine. 
Apart from these compounds, other forms of organic sulfur include sulfolipids, 
phytoalexins, redox compounds and many flavor and fragrance imparting 
compounds, such as diallyls of onion and garlic and the glucosinolates of 
brassicas and other crucifers.  
 
Sulphur Metabolism 
 
5 
Institute of Lifelong Learning, University of Delhi 
 
Biogeochemical sulfur cycle 
The biogeochemical sulfur cycle involves interconversion of oxidized and reduced 
sulfur states on Earth. Both plants and microorganisms can reduce sulfate to 
sulfite for assimilation of sulfur into S-containing amino acid cysteine and other 
organic sulfur compounds. In nature, sulfate reduction predominantly takes 
place by microbial SO
4
2-
 reduction, where facultative anaerobic bacteria like 
Pseudomonas and Salmonella use sulfate as a respiratory electron acceptor and 
reduce it to sulfur, and this sulfur is further reduced by Desulfovibrio, 
Desulfomonas and other anaerobes. This pathway, known as dissimilation, 
generates huge amounts of H
2
S. 
Oxidative phase of the cycle which involves regeneration of SO
4
2-
 from S and 
H
2
S, completes the cycle. Oxidation can take place in following  ways: 
a) Biological oxidation by a range of organisms, including chemoautotrophic 
bacteria which use reduced sulfur compounds as electron donors for 
chemosynthetic or photosynthetic reactions, 
b) Biological oxidation by various aerobes (e.g. Thiobacillus) and anaerobes 
(e.g.Chlorobium) which oxidize sulfite to sulfur and further to sulfate, 
c) Spontaneous geochemical oxidation of sulfide to gaseous sulfur dioxide (SO
2
) 
at neutral pH and 
d) Combustion of fossil fuels produces SO
2
.
 
SO
2
 can then be taken up and assimilated by leaves and more generally, can 
enter water or soil as the dissolved form of SO
3
2-
.