INFLUENCE OF LIGHT ON CHEMICAL 



INHIBITION OF LETTUCE 



SEED GERMINATION 



By ROBERT L. WEINTRAUB i 

 Division of Radiation and Organisms, Smithsonian Institution 



INTRODUCTION 



It is well known that some lots of lettuce seed (Lactitca saliva L.), 

 under particular environmental conditions, will give a higher percent- 

 age germination if exposed to light than if maintained in darkness 

 during the germination test (Larson and Ure, 1924; Shuck, 1933, 

 1934; Flint, 1934a, 1934&, 193s, 1936; Flint and McAHster, 1937; 

 Thompson, 1938). This response, which is found also in many other 

 species and has been termed "light-sensitivity," is influenced by several 

 factors including the variety, storage history of the particular seed lot, 

 temperature and water supply during the test, and characteristics of 

 the irradiation treatment. No systematic study of the role of the in- 

 fluential factors has been reported for lettuce seed, and there is very 

 little information as to the mechanism of light-sensitivity in general. 

 One suggested mechanism is that dormancy is caused by the presence 

 in the seed of a growth inhibitor which is somehow rendered inactive 

 by light. 



There exists a considerable body of evidence that dormancy of a 

 number of species is controlled, or at least influenced, by chemical 

 inhibitors present in, or formed by, the seed or fruit (for literature 

 citations see Stout and Tolman, 1941 ; Nutile, 1944, 1945). The pres- 

 ence of such inhibitors in lettuce has been invoked as an explanation 

 for various aspects of dormancy (Borthwick and Robbins, 1928; 

 Shuck, 1934), and evidence for the formation of germination inhibitors 

 by this species has been reported by Shuck (1935) and by Stout and 

 Tolman. Similar evidence, to be published separately, has been ob- 

 tained by the writer. 



Nutile (1944, 1945) discovered that in darkness low concentrations 

 of coumarin prevented germination of lettuce seed under conditions 



1 Now with the Department of the Army, Camp Detrick, Frederick, Md. 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. :07, NO. 20 



