126 MUTATION AND PLANT BREEDING 



ide. Mutation frequency is enhanced in Drosophila $ $ whose cata- 

 lase has been poisoned by KCN (83, 84). Under these conditions, 

 formaldehyde injection even produces some mutations in 9 9 , which 

 otherwise are quite refractory to it. Solutions of formaldehyde are 

 but weakly mutagenic for conidia of Neurospora; so are solutions 

 of hydrogen peroxide (46). A mixture of both compounds in solution 

 is strongly mutagenic (28), and addition of dihydroxydimethyl 

 peroxide compound is a good mutagen for Drosophila (82). 



When formaldehyde is applied as an admixture to the food 

 of Drosophila, it probably acts in quite a different way. While 

 injection produces mutations mainly in mature spermatozoa, form- 

 aldehyde food acts preferentially or exclusively on the long- 

 growth stage of the primary spermatocyte that, in the larvae, pre- 

 cedes meiosis (9). Female larvae are wholly resistant to formaldehyde 

 food; so are adults. Experiments with isotopically labelled formal- 

 dehyde (47) have shown that lack of penetration into certain cells 

 cannot be responsible for these results; for large amounts of labelled 

 formaldehyde were found inside the germ cells of adults, of female 

 larvae, and of spermatogonia. The fact that bunches of identical 

 or complementary cross-overs were obtained from treated $ larvae 

 (85) shows that the effective substance enters the nucleus of sperma- 

 togonia; yet it hardly, if ever, produces mutations at this stage, 

 for several hundred cross-tests between autosomal lethals that 

 appeared as clusters in the progeny of individual $ £ yielded no 

 clusters of identical lethals (9). 



It is tempting to assume that the preferential mutagenic action 

 of formaldehyde food on the growth stage of the primary sperma- 

 tocyte is somehow connected with the synthetic processes going on 

 during this stage. This assumption is supported by various observa- 

 tions. Thus, any condition that slows down larval development 

 reduces the mutagenic effectiveness of formaldehyde food (8). More 

 recently, Alderson found that, in a synthetic and sterile medium, 

 formaldehyde requires adenosine riboside for its mutagenic action 

 (1,2). 



Substances Related to Nucleic Acid 



Even before DNA acquired its predominant role in our model 

 of the genetic material, substances related to nucleic acid metab- 

 olism Avere tested for mutagenic activity, many of them with success. 



