Principles of Plant Breeding (2+1)

Chemical mutagens

Chemical Mutagen

Chemical Mutagen

• The material is soaked in a solution of the mutagen to induce mutations.
  
• Chemical mutagens are generally carcinogenic and must be used with great caution.
  
• One of the most effective chemical mutagenic groups is the group of alkylating agents (these react with the DNA by alkylating the phosphate groups as well as the purines and pyrimidines).
  
• Another group is the base analogues (they are closely related to the DNA bases and can be wrongly incorporated during replication); examples are 5-bromo uracil and maleic hydrazine. (Chemical mutagens commonly used are ethyl methane sulfonate (EMS) and diethylsulfonate (DES).
  
• The half-life (time taken for degradation of the initial amount of alkylating agent) for EMS in water is about 3 hours at 20°C but only 10 hours at 37°C.
  
• Consequently, chemical mutagens are best freshly prepared for each occasion.
Mutagen group	Examples
Base analogues	5-bromouracil, 5-bromodeoxyuridine
Related compounds	Maleic hydrazide, 8-ethoxy caffeine
Antibiotics	Actinomycin D, Mitomycin C, Streptonigrin
Alkylating agents	Sulfur mustards Ethyl–2-chloroethyl sulfide Nitrogen mustards 2-chloroethyl-dimethyl amine Epoxides Ethylene oxide Ethyleneimines Ethyleneimine Sulfonates, etc. Ethyl methane sulfonate (EMS), Diethylsulfonate (DES)
Diazoalanes Nitroso compounds Azide Hydroxylamine Nitrous acid Acridines	Diazomethane N-ethyl-N-nitroso urea Sodium azide Hydroxylamine Nitrous acid Acridine orange