Role of Coumarins in Growth and Germination 737 



apical dominance in sugar cane by Burr (8), reduction of permeability 

 by Guttenberg and Beythien (19), Guttenberg and Meinl (20), and 

 Reiff and Guttenberg (66), and growth inhibition in chicory by Grail- 

 lot (18). The inhibitory action of coumarin on barley growth and 

 its possible use in brewing has been discussed by Cook (10) and by 

 Kirsop and Pollock (24). 



A specific effect of coumarin on dehydrogenases has been claimed. 

 Marre (36) states that coumarin, at concentrations of lO-^ M inhibits 

 glucose-6-phosphate dehydrogenase activity in vitro. In contrast, Kuhn, 

 Pfleiderer, and Schulz (26) claim that 10-2 m coumarin enhances by 

 two- to threefold the citric acid dehydrogenase activity of maize seeds. 

 No in vitro effect of coumarin (0.7 X lO-s M) on dehydrogenase 

 activity of lettuce seeds could be shown by Mayer, Poljakoff-Mayber, 

 and Appleman (45) although when the seeds were germinated in the 

 same concentration of coumarin, the development of dehydrogenase 

 activity was inhibited in vivo. 



A relationship between the effects of coumarins and auxins in 

 growth and metabolism has been suggested by Libbert (32) and 

 Reinders-Gouwentak and Smeets (67). But Libbert and Liibke (33, 34) 

 failed to prove that scopoletin is identical with the natural inhibitor. 

 Thimann and Bonner (79), using the straight growth test, found that 

 coumarin inhibited the lAA induced growth of Aveyia coleoptiles, 

 and showed that this inhibition could be reversed by BAL. This, 

 however, is contradicted by San Antonio (72), who reported that cou- 

 marin does not inhibit Avena elongation in the presence of lAA. He, 

 however, used the curvature test. Gortner, Kent, and Sutherland (17) 

 assign to the coumarin derivatives, p-coumaric and ferulic acids, an 

 effect on lAA oxidase. An inhibition of this enzyme system by cou- 

 marin itself has been reported by Blumenthal-Goldschmidt (6). 



Reports of stimulatory effects of coumarin are of special interest. 

 It seems very probable that the action of coumarin in stimulating or 

 inhibiting growth and germination is closely related to its concentra- 

 tion. Germination stimulation similar to that caused by lAA was 

 shown by Lavollay and Laborey (29) for barley, using lO-"^ to lO-io M 

 coumarin, while Evenari observed stimulation by low concentration 

 in lettuce. Van Sumere et al. (76) showed that coumarin enhanced the 

 germination of uredospores of wheat rust. Miller and Meyer (47) found 

 that coumarin in concentrations of 1 to 200 p.p.m. stimulated the 

 leaf expansion of Chenopodium in the presence of KNO3 and glu- 

 cose. Winter (81), as already stated, observed stimulation of cambial 

 activity in Helianthus and Phaseolus plants, caused by the application 

 of 0.5 mg. coumarin per plant. Tarragan (77) demonstrated stimula- 

 tion of the growth of tomato roots in tissue culture by very low cou- 



