740 A. M. Mayer and A. Poljakoff-Mayber 



coumaric acid) were less active in promoting elongation than cou- 

 marin. Here again the need for the lactone structure seems clearly es- 

 tablished. The fact that both 3- and 4-hydroxy substitution converts 

 coumarin fi'om stimulator to inhibitor is somewhat surprising. On 

 theoretical grounds it would be expected that 3-substitution affects the 

 ring quite differently from 4-substitution. From the work with cou- 

 marin derivatives it seems that the double bond is of special signifi- 

 cance in the stimulation of growth, as well as in its inhibition. Norman 

 and Weintraub (53) also stressed the importance of this double bond, 

 and pointed out that all the naturally occurring active derivatives 

 have the 3 and 4 positions free. 



The 3- and 4-hydroxycoumarins are not only themselves inhibitors 

 but also counteract the stimulation caused by coumarin. Hydroxy sub 

 stitution may markedly affect the activity of other sites in the coumarin 

 molecule and change the ease of ring opening. The 4-hydroxycou- 

 marin can enolize readily with the carbonyl group but it is less easy to 

 visualize such an effect for the 3-hydroxycoumarin. 6-Hydroxycou- 

 marin was almost as active as the unsubstituted coumarin in pro- 

 moting extension growth. This work of Neumann is the first attempt 

 to elucidate the connection between the structure and growth stimula- 

 tory action of the coumarin derivatives and clearly requires extension. 



Tiie fact that germination inhibition and growth stimulation re- 

 quire somewhat different structural configuration is of special im- 

 portance (Table 1). Germination and growth are differently affected 

 by various agents and they are apparently two different processes, 

 germination being a process of its own and not simply a result of 

 embryo growth. Both processes involve numerous steps, one or more 

 of which may be rate limiting. Altering the rate of such a step will 

 materially affect the whole process and will consequently be of great 

 importance in the development of the organism. Coumarin may be 

 such an agent which acts on different rate-limiting steps in growth 

 and germination. 



In our laboratory an attempt was made to elucidate the mode of 

 action of coumarin by studying the effect of coumarin on various 

 metabolic changes in germinating lettuce seeds, as well as its effect on 

 the activity of various enzymes both in vitro and in vivo. These re- 

 sults are summarized in Table 2. 



Generally speaking, coumarin, when applied to whole seeds, i.e., 

 in vivo, inhibits germination and therefore various enzymes are not 

 formed or do not increase in activity. However, proteinase, and a 

 neutral lipase are very markedly inhibited by coumarin in vitro as 

 well (Table 2). It is known that even dry seeds already contain a con- 

 siderable ninnbcr of enzymes and their presence can be demonstrated 



