Role of Coumarins in Growth and Germination 743 



(40). The phosphorus compounds in lettuce seeds were fractionated 

 into trichloracetic acid (TCA) soluble, HCl soluble, and hydrolyzable 

 during 7 min. at 100° C, and into residual phosphorus (Poljakoff- 

 Mayber, unpublished). The TCA soluble fraction decreased with 

 germination while the others increased. The TCA fraction contains 

 phytin, phosphorylated sugars, as well as adenosine phosphates and 

 small amounts of inorganic phosphate. As germination proceeded, the 

 amount of ATP apparently decreased but increased again with subse- 

 quent growth. When the seeds were germinated in coumarin the ATP 

 spot on the chromatograms did not decrease in size and the fructose 

 1,6-phosphate spot was absent (15). These observations may be related 

 to the fact that phytin decomposition was prevented and phytase 

 activity was almost absent in seeds germinated in coumarin. Since, 

 as has been pointed out above, half of the phosphorus in dry seeds 

 is present as phytin, coumarin may in this way block the inorganic 

 phosphorus supply. On the other hand, the changes in the phosphory- 

 lated intermediates noted above may indicate a more direct inter- 

 ference in phosphate metabolism. In this connection it is of interest 

 that mitochondria-free extracts of peas germinated in coumarin show 

 glycolytic phosphorylation, i.e., ATP formation, to the same extent 

 as do the controls. Thus, here neither the glycolysis nor the enzymes 

 transferring phosphate to ATP were affected by the coumarin (Mayer, 

 unpublished). It is possible that in lettuce glycolysis begins at a 

 somewhat later stage of development than in peas and that the energy 

 releasing processes are different during germination proper and dur- 

 ing the subsequent growth. This is suggested by the changes in ac- 

 tivity of the tricarboxylic acid cycle enzymes during germination (60). 

 Some interesting information can be obtained from a study of 

 interaction between coumarin and thiourea and their eflfect on germi- 

 nation and growth. Thiourea stimulates the germination in the dark 

 of light-sensitive lettuce seeds but strongly inhibits the growth of the 

 lettuce seedlings. Treatment of seeds with coumarin makes them more 

 sensitive to thiourea, i.e., the maximum stimulatory effect on germina- 

 tion is evident at lower concentrations of thiourea (2.5 X 10"^ ^)- 

 The higher concentration (5 X 10"^ M), which in the absence of cou- 

 marin causes the maximal effect, is much less effective in its presence. 

 As a result an optimum response curve to thiourea appears in cou- 

 marin-treated seeds which is absent in non-treated ones in the range of 

 thiourea concentrations used (62). Thiourea and coumarin also inter- 

 act in their effect on the growth of lettuce seedlings. An antagonistic 

 effect of the two substances in their effect on germination is also re- 

 ported by Lavollay and Laborey (27, 28). The interaction between the 

 two substances in their effect on germination and growth may be 



